Hard X-ray Emission from Cassiopeia A SNR
二叠纪-三叠纪灭绝事件
二叠纪-三叠纪灭绝事件二叠纪-三叠纪灭绝事件（Permian–Triassic extinction event）是一个大规模物种灭绝事件，发生于古生代二叠纪与中生代三叠纪之间，距今大约2亿5140万年[1][2]。
若以消失的物种来计算，当时地球上70%的陆生脊椎动物，以及高达96%的海中生物消失[3]；这次灭绝事件也造成昆虫的唯一一次大量灭绝。
计有57%的科与83%的属消失[4][5]。
在灭绝事件之后，陆地与海洋的生态圈花了数百万年才完全恢复，比其他大型灭绝事件的恢复时间更长久[3]。
此次灭绝事件是地质年代的五次大型灭绝事件中，规模最庞大的一次，因此又非正式称为大灭绝（Great Dying）[6]，或是大规模灭绝之母（Mother of all mass extinctions）[7]。
二叠纪-三叠纪灭绝事件的过程与成因仍在争议中[8]。
根据不同的研究，这次灭绝事件可分为一[1]到三[9]个阶段。
第一个小型高峰可能因为环境的逐渐改变，原因可能是海平面改变、海洋缺氧、盘古大陆形成引起的干旱气候；而后来的高峰则是迅速、剧烈的，原因可能是撞击事件、火山爆发[10]、或是海平面骤变，引起甲烷水合物的大量释放[11]。
目录? 1 年代测定? 2 灭绝模式o 2.1 海中生物o 2.2 陆地无脊椎动物o 2.3 陆地植物? 2.3.1 植物生态系统? 2.3.2 煤层缺口o 2.4 陆地脊椎动物o 2.5 灭绝模式的可能解释? 3 生态系统的复原o 3.1 海洋生态系统的改变o 3.2 陆地脊椎动物? 4 灭绝原因o 4.1 撞击事件o 4.2 火山爆发o 4.3 甲烷水合物的气化o 4.4 海平面改变o 4.5 海洋缺氧o 4.6 硫化氢o 4.7 盘古大陆的形成o 4.8 多重原因? 5 注释? 6 延伸阅读? 7 外部链接年代测定在西元二十世纪之前，二叠纪与三叠纪交界的地层很少被发现，因此科学家们很难准确地估算灭绝事件的年代与经历时间，以及影响的地理范围[12]。
市售干海参中非法添加的蔗糖和无机成分的X射线衍射质量控制
市售干海参中非法添加的蔗糖和无机成分的X射线衍射质量控制路大勇1,2，项太平1（1.吉林化工学院材料科学与工程学院，吉林吉林 132022）（2.吉林省高校特种功能材料重点实验室，吉林吉林 132022）摘要：粉末X射线衍射（PXRD）是一种简单快捷的无损检测技术，该技术罕有海参及其非法添加剂的检测应用。
本研究建立一种干海参中非法添加糖分的PXRD鉴定方法。
对随机采购的8种市售干海参刺参（呈甄干海参、棒棰岛干海参、辽刺参、精品海参、俄罗斯海参、野生海参、财神岛干海参、长生岛干海参），获得PXRD谱及特征标记峰。
运用有机分子晶体的PXRD谱模拟方法，鉴定糖分来源及其含量。
结果表明：海参体壁没有任何种类的有机分子晶体，海参沙嘴主要成分为具有菱方结构的碳酸镁钙（Mg0.1Ca0.9CO3），人为掺入的蔗糖能够在干海参中结晶，形成能被PXRD技术探测的系列衍射峰。
辽刺参中掺有糖分，被鉴定为蔗糖，其含量达4.45 g/100 g；呈甄干海参、棒棰岛干海参、辽刺参、精品海参、俄罗斯海参、野生海参、财神岛干海参、长生岛干海参中盐分含量分别为：3.62 g/100 g、4.40 g/100 g、3.55 g/100 g、2.87 g/100 g、1.60 g/100 g、15.56 g/100 g、2.35 g/100 g、3.90 g/100 g；呈甄干海参、棒棰岛干海参、精品海参、俄罗斯海参、野生海参、财神岛干海参、长生岛干海参中含沙量分别为：2.12 g/100 g、0.62 g/100 g、0.14 g/100 g、0.22 g/100 g、0.38 g/100 g、0.85 g/100 g、0.90 g/100 g。
因此，PXRD技术适合于市售干海参糖分和盐分的质量控制。
关键词：干海参；食品安全；粉末X射线衍射；盐分；蔗糖；碳酸镁钙文章篇号：1673-9078(2021)05-262-270 DOI: 10.13982/j.mfst.1673-9078.2021.5.0906 X-ray Diffraction Quality Control of the Illegally Added Sucrose and Inorganic Components in Commercial Dried Sea CucumberLU Da-yong1,2, XIANG Tai-ping1(1.College of Materials Science and Engineering, Jilin Institute of Chemical Technology, Jilin 132022, China)(2.Key Laboratory for Special Functional Materials in Jilin Provincial Universities, Jilin 132022, China)Abstract: Powder X-ray diffraction (PXRD) is a simple and rapid non-destructive test technique, which has rarely been applied to the detection of sea cucumber and its illegal additives. In this work, a PXRD identification method was set up for detecting illegally-added sugar in dried sea cucumber. Eight kinds of commercial dried sea cucumbers (Cheng Zhen dried Sea cucumber, Bangchui Island dried sea cucumber, Liao sea cucumber, high-quality sea cucumber, Russian sea cucumber, wild sea cucumber, Caishen Island dried sea cucumber and Changsheng Island dried sea cucumber) were purchased randomly, and their PXRD patterns and characteristic mark peaks were obtained. The PXRD spectrum simulation of organic molecular crystals was applied to identify the origin and content of the sugar in the sea cucumbers. The results indicated that there were no organic molecular crystals existed in the body walls of sea cucumber, and the main component of sea cucumber sand mouth was magnesium calcium carbonate (Mg0.1Ca0.9CO3) with a rhombohedral structure. The artificially incorporated sucrose could crystallize 引文格式：路大勇,项太平.市售干海参中非法添加的蔗糖和无机成分的X射线衍射质量控制[J].现代食品科技,2021,37(5):262-270,337LU Da-yong, XIANG Tai-ping. X-ray diffraction quality control of the illegally added sucrose and inorganic components in commercial dried sea cucumber [J]. Modern Food Science and Technology, 2021, 37(5): 262-270,337收稿日期：2020-09-28基金项目：长白山学者特聘教授支持计划（2015047）；吉林省中医药科技委托重点项目（2020037）作者简介：路大勇（1967-），男，博士，教授，研究方向：高介电陶瓷材料、变温测试技术、晶体药物及中药质量控制、无机-有机复合材料、胆结石精准鉴定与医疗262in dried sea cucumber, thereby forming a series of diffraction peaks that were detected by PXRD technique. Sucrose was illegally added to Liao sea cucumber at a content of 4.45 g/100 g. The salt contents of Cheng Zhen dried Sea cucumber, Bangchui Island dried sea cucumber, Liao sea cucumber, high-quality sea cucumber, Russian sea cucumber, wild sea cucumber, Caishen Island dried sea cucumber and Changsheng Island dried sea cucumber were 3.62 g/100 g, 4.40 g/100 g, 3.55 g/100 g, 2.87 g/100 g, 1.60 g/100 g, 15.56 g/100 g, 2.35 g/100 g and 3.90 g/100 g, respectively. The sand contents of Cheng Zhen dried sea cucumber, Bangchui Island dried sea cucumber, high-quality sea cucumber, Russian sea cucumber, wild sea cucumber, Caishen Island dried sea cucumber and Changsheng Island dried sea cucumber were 2.12 g/100 g, 0.62 g/100 g, 0.14 g/100 g, 0.22 g/100 g, 0.38 g/100 g, 0.85 g/100 g and 0.90 g/100 g, respectively. Thus, the PXRD technique is suitable for quality control of sugars and salt in commercial dried sea cucumber.Key words: dried sea cucumber; food safety; powder X-ray diffraction; salt; sucrose; magnesium calcium carbonate海参隶属于棘皮动物门（Echinodermata）海参纲（Holothrioider），是一种传统的名贵海产品，被誉为“八珍之首”。
Annu.Rev.Mater.Res.31_1_2001
Annu.Rev.Mater.Res.2001.31:1–23Copyright c2001by Annual Reviews.All rights reserved S YNTHESIS AND D ESIGN OF S UPERHARDM ATERIALSJ Haines,JM L´e ger,and G BocquillonLaboratoire de Physico-Chimie des Mat´e riaux,Centre National de la Recherche Scientifique,1place Aristide Briand,92190Meudon,France;e-mail:haines@cnrs-bellevue.fr;leger@cnrs-bellevue.frKey Words diamond,cubic boron nitride,carbon nitride,high pressure,stishovite s Abstract The synthesis of the two currently used superhard materials,diamond and cubic boron nitride,is briefly described with indications of the factors influencing the quality of the crystals obtained.The physics of hardness is discussed and the importance of covalent bonding and fixed atomic positions in the crystal structure,which determine high hardness values,is outlined.The materials investigated to date are described and new potentially superhard materials are presented.No material that is thermodynamically stable under ambient conditions and composed of light (small)atoms will have a hardness greater than that of diamond.Materials with hardness values similar to that of cubic boron nitride (cBN)can be obtained.However,increasing the capabilities of the high-pressure devices could lead to the production of better quality cBN compacts without binders.INTRODUCTIONDiamond has always fascinated humans.It is the hardest substance known,based on its ability to scratch any other material.Its optical properties,with the highest refraction index known,have made it the most prized stone in jewelry.Furthermore,diamond exhibits high thermal conductivity,which is nearly five times that of the best metallic thermal conductors (copper or silver)at room temperature and,at the same time,is an excellent electrical insulator,even at high temperature.In industry,the hardness of diamond makes it an irreplaceable material for grinding tools,and diamond is used on a large scale for drilling rocks for oil wells,cutting concrete,polishing stones,machining,and honing.The diamonds used for industry are now mostly man-made because their cutting edges are much sharper than those of natural diamonds,which have been eroded by geological time.The synthesis of diamond has been a goal of science from Moissant at the end of the nineteenth century to the successful synthesis under high pressures in 1955(1).However,diamond has a major drawback in that it reacts with iron and cannot be used for machining steel.This has prompted the synthesis of a second superhard0084-6600/01/0801-0001$14.001A n n u . R e v . M a t e r . R e s . 2001.31:1-23. D o w n l o a d e d f r o m a r j o u r n a l s .a n n u a l r e v i e w s .o r gb y C h i n e s e Ac ade m y of S c i e n c e s - L i b r a r y o n 05/16/09. F o r p e r s o n a l u s e o n l y .2HAINESL ´EGERBOCQUILLONmaterial,cubic boron nitride (cBN),whose structure is derived from that of dia-mond with half the carbon atoms being replaced by boron and the other half by nitrogen atoms.The resulting compound is half as hard as diamond,but it does not react with iron and can be used for machining steel.Cubic boron nitride does not exist in nature and is prepared under high-pressure high-temperature conditions,as is synthetic diamond.However,its synthesis is more difficult,and it has not been possible to prepare large crystals.Industry is thus looking for new superhard ma-terials that will need to be much harder than present ceramics (Si 3N 4,Al 2O 3,TiC).Hardness is a quality less well defined than many other physical properties.Hardness was first defined as the ability of one material to scratch another;this corresponds to the Mohs scale.This scale is highly nonlinear (talc =1,diamond =10);however,this definition of hardness is not reliable because materials of similar hardness can scratch each other and the resulting value depends on the specific details of the contact between the two materials.It is well known (2)that at room temperature copper can scratch magnesium oxide and at high temperatures cBN can scratch diamond (principle of soft indenter).Another,more accurate,way of defining and measuring hardness is by the indentation of the material by a hard indenter.According to the nature and shape of the indenter,different scales are used:Brinell,Rockwell,Vickers,and Knoop.The last two are the most frequently used.The indenter is made of a pyramidal-shaped diamond with a square base (Vickers),or elongated lozenge (Knoop).The hardness is deduced from the size of the indentation produced using a defined load;the unit is the same as that for pressure,the gigapascal (GPa).Superhard materials are defined as having a hardness of above 40GPa.The hardness of diamond is 90GPa;the second hardest material is cBN,with a hardness of 50GPa.The design of new materials with a hardness comparable to diamond is a great challenge to scientists.We first describe the current status of the two known super-hard materials,diamond and cBN.We then describe the search for new bulk super-hard materials,discuss the possibility of making materials harder than diamond,and comment on the new potentially superhard materials and their preparation.DIAMOND AND CUBIC BORON NITRIDE DiamondThe synthesis of diamond is performed under high pressure (5.5–6GPa)and high temperature (1500–1900K).Carbon,usually in the form of graphite,and a transi-tion metal,e.g.iron,cobalt,nickel,or alloys of these metals [called solvent-catalyst (SC)],are treated under high-pressure high-temperature conditions;upon heating,graphite dissolves in the metal and if the pressure and temperature conditions are in the thermodynamic stability field of diamond,carbon can crystallize as dia-mond because the solubility of diamond in the molten metal is less than that of graphite.Some details about the synthesis and qualities of diamond obtained by this spontaneous nucleation method are given below,but we do not describe the growthA n n u . R e v . M a t e r . R e s . 2001.31:1-23. D o w n l o a d e d f r o m a r j o u r n a l s .a n n u a l r e v i e w s .o r gb y C h i n e s e Ac ade m y of S c i e n c e s - L i b r a r y o n 05/16/09. F o r p e r s o n a l u s e o n l y .SUPERHARD MATERIALS 3of single-crystal diamond under high pressure,which is necessary in order to ob-tain large single crystals with dimensions greater than 1mm.Crystals of this size are expensive and represent only a very minor proportion of the diamonds used for machining;they are principally used for their thermal properties.It is well known that making diamonds is relatively straightforward,but control-ling the quality of the diamonds produced is much more difficult.Improvements in the method of synthesis since 1955have greatly extended the size range and the mechanical properties and purity of the synthetic diamond crystals.Depending on the exact pressure (P )and temperature (T )of synthesis,the form and the nature of the carbon,the metal solvent used,the time (t )of synthesis,and the pathways in P-T-t space,diamond crystals (3,4)varying greatly in shape (5),size,and fri-ability are produced.These three characteristics are used to classify diamonds;the required properties differ depending on the industrial application.Friability is related to impact strength.It is the most important mechanical property for the practical use of superhard materials,and low friability is required in order for tools to have a long lifetime.In commercial literature,the various types of diamonds are classed as a function of their uses,which depend mainly on their friabilities,but the numerical values are not given,so it is difficult to compare the qualities of diamonds from various sources.The friability,which is defined by the percentage of diamonds destroyed in a specific grinding process,is obtained by subjecting a defined quantity of diamonds to repeated impacts by grinding in a ball-mill or by the action of a load falling on them.The friability values depend strongly on the experimental conditions used,and only values for crystals measured under the same conditions can be compared.The effect of various synthesis parameters on their quality can be evaluated by considering the total mass of diamond obtained in one experiment,the distribution size of these diamonds,and the friability of the diamonds of a defined size.A first parameter is the source of the carbon.Most carbon-based substance can be used to make diamonds (6),but the nature of the carbon source has an effect on the quantity and the quality of synthetic diamonds.The best carbon source for diamond synthesis is graphite,and its characteristics are important.The effect of the density,gas permeability,and purity of graphite on the diamond yield have been investigated using cobalt as the SC (7).Variations of the density and gas permeability have no effect on the diamond yield,but carbon purity is important.The main impurity in synthetic graphite is CaO.If good quality diamonds are required,the calcium content should be kept below 1000ppm in order to avoid excessive nucleation on the calcium oxide particles.A second factor that alters the quality of diamonds is the nature of the SC.The friability and the size distribution are better with CoFe (alloy of cobalt with a small quantity of iron)than with invar,an iron-nickel alloy (Table 1:Ia,Ib;Figure 1a ).Another parameter is how the mixture of carbon and SC is prepared.When fine or coarse powders of intimately mixed graphite and SC are used,a high yield of diamonds with high friabilities is obtained (8).These diamonds are very small,A n n u . R e v . M a t e r . R e s . 2001.31:1-23. D o w n l o a d e d f r o m a r j o u r n a l s .a n n u a l r e v i e w s .o r g b y C h i n e s e A c a d e m y o f S c i e n c e s - L i b r a r y o n 05/16/09. F o r p e r s o n a l u s e o n l y .4HAINESL ´EGERBOCQUILLONTABLE 1Friabilities of some diamonds as a function of the details of the synthesis process fora selected size of 200–250µmSDA a MBS a 100+70Ia Ib IIa IIb IIc IIIa IIIb Synthesis CoFeInvar 1C-2SC 1C-1SC 2C-2SC Cycle A Cycle B detail stacking stacking stacking Friability 74121395053637250(%)aThe SDA 100+is among De Beers best diamond with a very high strength that is recommended for sawing the hardest stones and cast refractories.MBS 70is in the middle of General Electric’s range of diamonds for sawing and drilling.Other diamonds were obtained in the laboratory using a belt–type apparatus with a working chamber of 40mm diameter.(C,graphite;SC,solvent-catalyst.)with metal inclusions,and they are linked together with numerous cavities filled with SC.A favorable geometry in order to obtain well-formed diamonds is to stack disks of graphite and SC.The effect of local concentration has been exam-ined by changing the stacking of these disks (Table 1:IIa,IIb,IIc;Figure 1b ).The method of stacking modifies the local oversaturation of dissolved carbon and thus the local spontaneous diamond germination.For the synthesis of dia-mond,the heating current goes directly through the graphite-SC mixture.Because the electrical resistivity of the graphite is much greater than that of the SC,the temperature of the graphite is raised by the Joule effect,whereas that of the SC increases mainly because of thermal conduction.Upon increasing the thickness of the SC disk,the local thermal gradient increases and the dissolved atoms of carbon cannot move as easily;the local carbon oversaturation then enhances the spontaneous diamond germination.This enables one to work at lower tempera-tures and pressures,which results in slower growth and therefore better quality diamonds.Another important factor for the yield and the quality of the diamonds is the pathway followed in P-T-t space.The results of two cycles with the same final pressure and temperature are shown.In cycle A (Figure 1d ),the graphite-SC mixture reaches the eutectic melting temperature while it is still far from the equilibrium line between diamond and graphite;as a result spontaneous nucleation is very high and the seeds grow very quickly.These two effects explain the high yield and the poor quality and small size and high friability of the diamonds compared with those obtained in cycle B (Figure 1d ;see Table 1IIIa and IIIb and Figure 1c ).Large crystals (over 400µm)of good quality are obtained when the degree of spontaneous nucleation is limited.The pathway in P-T-t space must then remain near the graphite-diamond phase boundary (Figure 1d ),and the time of the treatment must be extended in the final P-T-t conditions.Usually,friability increases with the size of the diamonds.Nucleation takes place at the beginning of the synthesis when the carbon oversaturation is important,and the carbon in solution is then absorbed by the existing nuclei,which grow larger.A n n u . R e v . M a t e r . R e s . 2001.31:1-23. D o w n l o a d e d f r o m a r j o u r n a l s .a n n u a l r e v i e w s .o r g b y C h i n e s e A c a d e m y o f S c i e n c e s - L i b r a r y o n 05/16/09. F o r p e r s o n a l u s e o n l y .SUPERHARD MATERIALS5Figure 1Size distribution of diamonds in one laboratory run for different synthesis pro-cesses;effects of (panel a )the nature of the metal,(panel b )the stacking of graphite and metal disks,(panel c )the P-T pathway.(Panel d )P-T pathways for synthesis.1:graphite-diamond boundary and 2:melting temperature of the carbon-eutectic.The diamond synthesis occurs between the boundaries 1and 2.The growth time is about the same for all the crystals,thus those that can grow more quickly owing to a greater local thermal gradient become the largest.Owing to their rapid growth rate,they trap more impurities and have more defects,and therefore their friability is higher.Similarly,friability increases with the diamond yield.The diamonds produced by the spontaneous nucleation method range in size up to 800–1000µm.The best conditions for diamond synthesis correspond to a compromise between the quantity and the quality of the diamonds.A n n u . R e v . M a t e r . R e s . 2001.31:1-23. D o w n l o a d e d f r o m a r j o u r n a l s .a n n u a l r e v i e w s .o r g b y C h i n e s e A c a d e m y o f S c i e n c e s - L i b r a r y o n 05/16/09. F o r p e r s o n a l u s e o n l y .6HAINESL ´EGERBOCQUILLONCubic Boron NitrideCubic boron nitride (cBN)is the second hardest material.The synthesis of cBN isperformed in the same pressure range as that for diamond,but at higher tempera-tures,i.e.above 1950K.The general process is the same;dissolution of hexagonal boron nitride (hBN)in a solvent-catalyst (SC),followed by spontaneous nucle-ation of cBN.However,the synthesis is much more complicated.The usual SCs are alkali or alkaline-earth metals and their nitrides (9):Mg,Ca,Li 3N,Mg 3N 2,and Ca 3N 2.All these SCs are hygroscopic,and water or oxygen are poisons for the synthesis.Thus great care must be taken,which requires dehydration of the materials and preparation in glove boxes,to avoid the presence of water in the high-pressure cell.Furthermore,the above compounds react first with hBN to form inter-mediate compounds,Li 3BN 2,Mg 3B 2N 4,or Ca 3B 2N 4,which become the true SC.These compounds and the hBN source are electrical insulators,thus an internal furnace must be used,which makes fabrication of the high pressure cell more complicated and reduces the available volume for the samples.In addition,the chemical reaction involved is complicated by this intermediate step,and in gen-eral the yield of cBN is lower than for diamond.Work is in progress to determine in situ which intermediate compounds are involved in the synthesis process.The crystals of cBN obtained from these processes are of lower quality (Figure 2)and size than for diamond.Depending on the exact conditions,orange-yellow or dark crystals are obtained;the color difference comes from a defect or an excess of boron (less than 1%);the dark crystals,which have an excess of born,are harder.As in the synthesis of diamond,the initial forms of the SC source,hBN,play important roles,but the number of parameters is larger.For the source of BN,it is better to use pressed pellets of hBN powder rather than sintered hBN products,as the latter contain additives (oxides);a very fine powder yields a better reactivity.Doping of Li,Ca,or Mg nitrides with Al,B,Ti,or Si induces a change in the morphology and color of cBN crystals,which are dark instead of orange,are larger (500µm),have better shapes and,in addition,gives a higher yield (10).Use of supercritical fluids enables cBN to be synthesized at lower pressures and temperatures (2GPa,800K),but the resulting crystal size is small (11).Diamond and cBN crystals are produced on a large scale,and the main problem is how to use them for making viable tools for industry.Different compacts of these materials are made (12)for various pacts of diamonds are made using cobalt as the SC.The mixture is treated under high-pressure high-temperature conditions,at which superficial graphitization of the diamonds takes place,and then under the P-T-t diamond synthesis conditions so as to transform the graphite into diamond and induce intergranular growth of diamonds.The diamond compacts produced in this way still contain some cobalt as a binder,but their hardness is close to that of single-crystal pacts of cBN cannot be made in the same way because the SCs are compounds that decompose in air.Sintering without binders (13)is possible at higher pressures of about 7.5–8GPa and temperatures higher than 2200K,but these conditions are currently outside the range of thoseA n n u . R e v . M a t e r . R e s . 2001.31:1-23. D o w n l o a d e d f r o m a r j o u r n a l s .a n n u a l r e v i e w s .o r g b y C h i n e s e A c a d e m y o f S c i e n c e s - L i b r a r y o n 05/16/09. F o r p e r s o n a l u s e o n l y.SUPERHARD MATERIALS7Figure 2SEM photographs of diamond (top )and cBN (bottom )crystals of different qualities depending on the synthesis conditions (the long vertical bar corresponds to a distance of 100µm).Top left :good quality mid-sized diamonds of cubo-octahedral shape with well-defined faces and sharp edges;top right :lower quality diamonds;bottom left :orange cBN crystals;bottom right :very large black cBN crystals of better shapes.A n n u . R e v . M a t e r . R e s . 2001.31:1-23. D o w n l o a d e d f r o m a r j o u r n a l s .a n n u a l r e v i e w s .o r g b y C h i n e s e A c a d e m y o f S c i e n c e s - L i b r a r y o n 05/16/09. F o r p e r s o n a l u s e o n l y .8HAINESL ´EGERBOCQUILLONused in industrial pacts of cBN with TiC or TaN binders are ofmarkedly lower hardness because there is no direct bonding between the superhard crystals,in contrast to diamond compacts.In addition,they are expensive,and this has motivated the search for other superhard materials.SEARCH FOR NEW SUPERHARD MATERIALSOne approach for increasing hardness of known materials is to manipulate the nanostructure.For instance,the effect of particle size on the hardness of materials has been investigated.It is well known that high-purity metals have very low shear strengths;this arises from the low energy required for nucleation and motion of dislocations in metals.The introduction of barriers by the addition of impurities or grain size effects may thus enhance the hardness of the starting phase.In this case,intragranular and intergranular mechanisms are activated and compete with each other.As each mechanism has a different dependency on grain size,there can be a maximum in hardness as the function of the grain size.This effect of increasing the hardness with respect to the single-crystal value does not exist in the case of ceramic materials.In alumina,which has been thoroughly studied,the hardness (14)of fine-grained compacts is at most the hardness of the single crystal.When considering superhard materials,any hardness enhancement would have to come from the intergranular material,which would be by definition of lower hard-ness.In the case of thin films,it has been reported that it is possible to increase the hardness by repeating a layered structure of two materials with nanometer scale dimensions,which are deposited onto a surface (15).This effect arises from the repulsive barrier to the movement of dislocations across the interface between the two materials and is only valid in one direction for nanometer scale defor-mations.This could be suitable for coatings,but having bulk superhard materials would further enhance the unidirectional hardness of such coatings.In addition,hardness in these cases is determined from tests at a nanometer scale with very small loads,and results vary critically (up to a factor of three)with the nature of the substrate and the theoretical models necessary to estimate quantitatively the substrate’s influence (16).We now discuss the search for bulk superhard materials.Physics of HardnessThere is a direct relation between bulk modulus and hardness for nonmetallic ma-terials (Figure 3)(17–24),and here we discuss the fundamental physical properties upon which hardness depends.Hardness is deduced from the size of the inden-tation after an indenter has deformed a material.This process infers that many phenomena are involved.Hardness is related to the elastic and plastic properties of a material.The size of the permanent deformation produced depends on the resistance to the volume compression produced by the pressure created by the indenter,the resistance to shear deformation,and the resistance to the creation and motion of dislocations.These various types of resistance to deformation indicateA n n u . R e v . M a t e r . R e s . 2001.31:1-23. D o w n l o a d e d f r o m a r j o u r n a l s .a n n u a l r e v i e w s .o r g b y C h i n e s e A c a d e m y o f S c i e n c e s - L i b r a r y o n 05/16/09. F o r p e r s o n a l u s e o n l y .SUPERHARD MATERIALS 9Figure 3Hardness as a function of the bulk modulus for selected materials (r-,rutile-type;c,cubic;m,monoclinic).WC and RuO 2do not fill all the requirements to be superhard (see text).which properties a material must have to exhibit the smallest indentation possible and consequently the highest hardness.There are three conditions that must be met in order for a material to be hard:The material must support the volume decrease created by the applied pressure,therefore it must have a high bulk modulus;the material must not deform in a direction different from the applied load,it must have a high shear modulus;the material must not deform plastically,the creation and motion of the dislocations must be as small as possible.These conditions give indications of which materials may be superhard.We first consider the two elastic properties,bulk modulus (B)and shear modulus (G),which are related by Poisson’s ratio (ν).We consider only isotropic materials;a superhard material should preferably be isotropic,otherwise it would deform preferentially in a given direction (the crystal structure of diamond is isotropic,but the mechanical properties of a single crystal are not fully isotropic because cleavage may occur).In the case of isotropic materials,G =(3/2)B (1−2ν)/(1+ν);In order for G to be high,νmust be small,and the above expression reduces thenA n n u . R e v . M a t e r . R e s . 2001.31:1-23. D o w n l o a d e d f r o m a r j o u r n a l s .a n n u a l r e v i e w s .o r g b y C h i n e s e A c a d e m y o f S c i e n c e s - L i b r a r y o n 05/16/09. F o r p e r s o n a l u s e o n l y .10HAINESL ´EGERBOCQUILLONto G =(3/2)B (1−3ν).The value of νis small for covalent materials (typicallyν=0.1),and there is little difference between G and B:G =1.1B.A typical value of νfor ionic materials is 0.25and G =0.6B;for metallic materials νis typically 0.33and G =0.4B;in the extreme case where νis 0.5,G is zero.The bulk and shear moduli can be obtained from elastic constants:B =(c 11+2c 12)/3,G =(c 11−c 12+3c 44)/5.Assuming isotropy c 11−c 12=2c 44,it follows that G =c 44;Actually G is always close to c 44.In order to have high values of B and G,then c 11and c 44must be high with c 12low.This is the opposite of the central forces model in which c 12=c 44(Cauchy relation).The two conditions,that νbe small and that central forces be absent,indicate that bonding must be highly directional and that covalent bonding is the most suitable.This requirement for high bulk moduli and covalent or ionic bonding has been previously established (17–19,21–24)and theoretical calculations (19,25,26)over the last two decades have aimed at finding materials with high values of B (Figure 3).The bulk modulus was used primarily for the reason that it is cheaper to calculate considering the efficient use of computer time,and an effort was made to identify hypothetical materials with bulk moduli exceeding 250–300GPa.At the present time with the power of modern computers,elastic constants can be obtained theoretically and the shear modulus calculated (27).The requirement for having directional bonds arises from the relationship be-tween the shear modulus G and bond bending (28).Materials that exhibit lim-ited bond bending are those with directional bonds in a high symmetry,three-dimensional lattice,with fixed atomic positions.Covalent materials are much better candidates for high hardness than ionic compounds because electrostatic interac-tions are omnidirectional and yield low bond-bending force constants,which result in low shear moduli.The ratio of bond-bending to bond-stretching force constants decreases linearly from about 0.3for a covalent material to essentially zero for a purely ionic compound (29,30).The result of this is that the bulk modulus has very little dependence on ionicity,whereas the shear modulus will exhibit a relative de-crease by a factor of more than three owing entirely to the change in bond character.Thus for a given value of the bulk modulus,an ionic compound will have a lower shear modulus than a covalent material and consequently a lower hardness.There is an added enhancement in the case of first row atoms because s-p hybridization is much more complete than for heavier atoms.The electronic structure also plays an important role in the strength of the bonds.In transition metal carbonitrides,for example,which have the rock-salt structure,the hardness and c 44go through a maximum for a valence electron concentration of about 8.4per unit cell (31).The exact nature of the crystal and electronic structures is thus important for determin-ing the shear modulus,whereas the bulk modulus depends mainly on the molar volume and is less directly related to fine details of the structure.This difference is due to the fact that the bulk modulus is related to the stretching of bonds,which are governed by central forces.Materials with high bulk moduli will thus be based on densely packed three-dimensional networks,and examples can be found among covalent,ionic,and metallic materials.In ionic compounds,the overall structure isA n n u . R e v . M a t e r . R e s . 2001.31:1-23. D o w n l o a d e d f r o m a r j o u r n a l s .a n n u a l r e v i e w s .o r g b y C h i n e s e A c a d e m y o f S c i e n c e s - L i b r a r y o n 05/16/09. F o r p e r s o n a l u s e o n l y .principally defined by the anion sublattice,with the cations occupying interstitial sites,and compounds with high bulk moduli will thus have dense anion packing with short anion-anion distances.The shear modulus,which is related to bond bending,depends on the nature of the bond and decreases dramatically as a func-tion of ionicity.In order for the compound to have a high shear modulus and high hardness (Figure 4),directional (covalent)bonding and a rigid structural topology are necessary in addition to a high bulk modulus.A superhard material will have a high bulk modulus and a three-dimensional isotropic structure with fixed atomic positions and covalent or partially covalent ionic bonds.Hardness also depends strongly on plastic deformation,which is related to the creation and motion of dislocations.This is not controlled by the shear modulus but by the shear strength τ,which varies as much as a factor of 10for different materials with similar shear moduli.It has been theoretically shown that τ/G is of the order of 0.03–0.04for a face-centered cubic metal,0.02for a layer structure such as graphite,0.15for an ionic compound such as sodium chloride,and 0.25for a purely covalent material such as diamond (32).Detailed calculationsmustFigure 4Hardness as a function of the shear modulus for selected materials (r-,rutile-type;c,cubic).A n n u . R e v . M a t e r . R e s . 2001.31:1-23. D o w n l o a d e d f r o m a r j o u r n a l s .a n n u a l r e v i e w s .o r g b y C h i n e s e A c a d e m y o f S c i e n c e s - L i b r a r y o n 05/16/09. F o r p e r s o n a l u s e o n l y .。
Hard X-ray and Infrared Emission from Apparently Single White Dwarfs
1
2
Chu et al.
Figure 1. ROSAT PSPC observations of KPD 0005+5106, PG 1159, and WD 2226−210. The top two rows show soft (0.1–0.4band images. The poor point-spread-function in the soft band is caused by an electronic ghost image at energies below 0.2 keV. The bottom row shows the PSPC spectra. To show the hard counts of PG 1159, its spectrum above 0.6 keV is scaled up by a factor of 50 as marked and plotted in open symbols.
arXiv:astro-ph/0701025v1 1 Jan 2007
**FULL TITLE** ASP Conference Series, Vol. **VOLUME**, **YEAR OF PUBLICATION** **NAMES OF EDITORS**
微藻的营养特性及其在畜牧业中应用的研究进展【论文】
微藻的营养特性及其在畜牧业中应用的研究进展摘要：微藻是一种分布广泛且营养物质含量高、光合能力强的自养植物。
微藻能合成多种拥有特殊生物活性的化合物, 还能提高动物的生长性能、增强机体免疫机能、改善畜产品品质、解决畜牧业的环境污染问题, 同时还可减轻食品与饲料以及燃料工业之间的竞争。
因此, 本文就微藻的营养特性及其对畜禽生长、免疫、产品品质等的影响进行综述, 为微藻在畜牧业中的开发和利用提供参考。
关键词：微藻; 生长; 免疫; 产品品质; 畜牧业;Abstract：Microalgae, a high photoautotrophy plant, is widely distributed and contained rich nutrient contents.M icroalgae can synthesize various special bioactive compounds, and play an important role in improving animal growth, immunity and meat quality, meanwhile, it can also curb environmental pollution and reduce competitive pressure among food, feed and fuel industry. Therefore, the nutritional characteristics of microalgae and its effects on animal growth and meat quality were reviewed in this paper so that it can provide a reference for the development and utilization ofmicroalgae in animal husbandry.Keyword：microalgae; grow th; immune; product quality; animal husbandry;到2050年, 全球人口预计将增加1/3, 估计粮食产量增加70%。
通常的化合物结晶是通过降温实现,但这篇钙钛矿的结晶是通过升温实现的,而且速度超快,还是单晶-2015-NC
of Physical Sciences and Engineering, Solar and Photovoltaics Engineering Research Center, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia. 2 Department of Chemistry, Faculty of Science, Mansoura University, Mansoura 35516, Egypt. 3 Mathematical Institute, University of Oxford, Woodstock Road, Oxford OX2 6GG, UK. 4 Materials Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia. 5 Imaging and Characterization Lab, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia. * These authors contributed equally to this work. Correspondence and requests for materials should be addressed to O.M.B. (email: osman.bakr@.sa).
Diffuse X-Ray Emission from the Quiescent Superbubble M17, the Omega Nebula
a rXiv:as tr o-ph/32579v127Fe b23Diffuse X-Ray Emission from the Quiescent Superbubble M 17,the Omega Nebula Bryan C.Dunne 1,You-Hua Chu 1,C.-H.Rosie Chen 1,Justin D.Lowry 1,Leisa Townsley 2,Robert A.Gruendl 1,Mart´ın A.Guerrero 1,and Margarita Rosado 3carolan@ ABSTRACT The emission nebula M 17contains a young ∼1Myr-old open cluster;the winds from the OB stars of this cluster have blown a superbubble around the cluster.ROSAT observations of M 17detected diffuse X-ray emission peaking at the cluster and filling the superbubble interior.The young age of the cluster suggests that no supernovae have yet occurred in M 17;therefore,it provides a rare opportunity to study hot gas energized solely by shocked stellar winds in a quiescent superbubble.We have analyzed the diffuse X-ray emission from M 17,and compared the observed X-ray luminosity of ∼2.5×1033ergs s −1and the hot gas temperature of ∼8.5×106K and mass of ∼1M ⊙to model predictions.We find that bubble models with heat conduction overpredict the X-ray luminosity by two orders of magnitude;the strong magnetic fields in M 17,as measured from H I Zeeman observations,have most likely inhibited heat conduction and associated mass evaporation.Bubble models without heat conduction can explain the X-ray properties of M 17,but only if cold nebular gas can be dynamically mixed into the hot bubble interior and the stellar winds are clumpy with mass-loss rates reduced by a factor of ≥3.Future models of the M 17superbubble must takeinto account the large-scale density gradient,small-scale clumpiness,and strong magnetic field in the ambient interstellar medium.Subject headings:ISM:bubbles —HII regions —ISM:individual (M17)—stars:early-type —stars:winds,outflows1.IntroductionMassive stars dynamically interact with the ambient interstellar medium(ISM)via their fast stellar winds and supernova ejecta.OB associations,with their large concentrations of massive stars,provide an excellent laboratory to study these interactions.The combined actions of the stellar winds and the supernovae from the massive stars in OB associations sweep up the ambient ISM to form expanding shells called superbubbles(Bruhweiler et al. 1980).The physical structure of a superbubble is very similar to that of a bubble blown by the stellar wind of an isolated massive star,as modeled by Castor,McCray,&Weaver (1975)and Weaver et al.(1977).Theoretically,an interstellar bubble consists of a shell of swept-up ISM with its interior filled by shocked fast wind at temperatures of106–108K.There are two basic types of models for wind-blown bubbles:energy-conserving and momentum-conserving.In the former,the shocked stellar wind is separated from the swept-up interstellar shell by a contact discontinu-ity,where heat conduction and mass evaporation may take place.The expansion of the shell is driven by the pressure of the hot interior gas(Dyson&de Vries1972;Castor et al.1975). In the momentum conserving bubbles,the fast stellar winds impinge on the swept-up shell directly,and the expansion is driven by the momentum of the fast stellar wind(Avedisova 1972;Steigman,Strittmatter,&Williams1975).One significant difference between a superbubble and a single star bubble is the possibil-ity that supernovae may occur inside a superbubble and introduce significant perturbations in the surface brightness and characteristic temperature of the X-ray emission,especially if a supernova explodes near the dense shell(Mac Low&McCray1988).This intermittent X-ray brightening has been observed in superbubbles in the Large Magellanic Cloud(LMC). Using Einstein and ROSAT observations,Chu&Mac Low(1990)and Dunne,Points,& Chu(2001)have reported diffuse X-ray emission from a large number of superbubbles in the LMC,and their X-ray luminosities all exceed the luminosities expected by Weaver et al.’s bubble model,indicating recent heating by supernovae.No LMC superbubbles in a quies-cent state,i.e.,without recent supernova heating,have been detected in X-rays by ROSAT (Chu et al.1995).It would be of great interest to detect diffuse X-ray emission from a qui-escent superbubble and compare it to model expectations,as this could provide a valuable diagnostic of bubble models.The emission nebula M17(from the catalog of Messier1850,α=18h21m,δ=−16◦10′(J2000.0),also known as the Omega Nebula,the Horseshoe Nebula,and NGC6618)is located on the eastern edge of a massive molecular cloud,M17SW(Lada,Dickinson,&Penfield 1974).M17exhibits a“blister-like”structure with an overall diameter of∼20′–25′,or∼10–12pc at an adopted distance of1.6kpc(Nielbock et al.2001).The nebula encompassesan open cluster with a stellar age of∼1Myr(Hanson,Howarth,&Conti1997).The open cluster is located on the western side of the nebula,which borders the molecular cloud. Arcuatefilaments extend eastward,creating a shell morphology,and suggesting that it is a young superbubble blown by the OB stars within.The young age of the cluster in M17 implies that no supernova explosions have occurred,thus M17provides an ideal setting to study the generation of hot gas solely by fast stellar winds inside a superbubble at a quiescent state.Recent Chandra observations of M17have revealed diffuse X-ray emission in the vicinity of the embedded open cluster(Townsley et al.2003).As a matter of fact,diffuse X-ray emis-sion from M17over a more extended area was previously detected in a ROSAT observation but was never reported.We have analyzed this diffuse X-ray emission from the interior of M17detected by ROSAT to determine the physical properties of the hot interior gas,and considered bubble models with and without heat conduction.Wefind that models with heat conduction produce results with the largest discrepancy from the observed X-ray luminos-ity and hot gas temperature and mass of the superbubble in M17.This paper reports our analysis of the ROSAT observations of M17and comparisons to a range of bubble models.2.Observations and Data Reduction2.1.ROSAT Archival DataWe have used an archival ROSAT Position Sensitive Proportional Counter(PSPC) observation to study the diffuse X-ray emission from M17and investigate the physical prop-erties of the hot,shocked gas interior to the superbubble.The PSPC is sensitive to X-rays in the energy range0.1–2.4keV and has an energy resolution of∼40%at1keV,with a field of view of∼2◦.Further information on the PSPC can be found in the ROSAT Mission Description(1991).The PSPC observation of M17(sequence number RP500311,PI:Aschenbach)was ob-tained on1993September12–13.It is centered on the nebula atα(J2000)=18h21m04.s78 andδ(J2000)=−16◦10′12.′′0,and has an exposure time of6.7ks.As M17has an angular size of∼20′–25′,the diffuse X-ray emission from the superbubble interior is well contained within the inner window support ring of the PSPC.The PSPC data were reduced using standard routines in the PROS4package under the IRAF5environment.2.2.Optical ImagingTo compare the spatial distribution of the X-ray-emitting gas with that of the cooler ionized gas in M17,we have obtained narrow-band Hαimages of this emission nebula.M17 was observed with the Mount Laguna1-m telescope on2002October28–31using a Tektronik 2K CCD.Afilter with peak transmission at6563˚A and a FWHM of20˚A was used to isolate the Hαline.Because the2K CCD has∼0.′′4pixels and afield-of-view of13.′6,the entire nebula could not be observed in a single exposure.Instead a total of twenty-four300s exposures were acquired at8positions to span the nebula.These exposures were combined to form a mosaic image of the nebula and to reject cosmic-ray events in the individual images using the methods outlined in Regan&Gruendl(1995).3.Analysis of the X-Ray EmissionSignificant X-ray emission is detected from M17in the PSPC observation,as can be seen in Figure1.To determine the nature and origin of this emission,we have analyzed its spatial distribution and spectral properties.We have examined the distribution of the X-ray emission and compared it to the optical morphology of the emission nebula.We have also extracted spectra from the PSPC data and modeled them to determine the physical conditions of the hot gas.3.1.Spatial Distribution of the X-ray EmissionTo study the spatial distribution of the X-ray emission from M17,the data were binned to5′′pixels and then smoothed with a Gaussian function ofσ=4pixels(see Figure1a). We have also taken our Hαmosaic and overlaid it with X-ray emission contours to study the extent of X-ray emission within the H II region(see Figure1b).Diffuse X-ray emission is observed to be well confined by the optical nebula.This diffuse emission shows no evidence of limb brightening,suggesting that the interior of M17is centrallyfilled with hot gas. The peak of the X-ray emission is coincident with the center of the open cluster in M17, where Chandra observations show a large number of point sources superposed on the diffuse emission(Townsley et al.2003).This spatial distribution suggests that the X-ray-emitting hot gas originates in the open cluster,as would be expected in a bubble blown by stellarwinds.As there is a massive molecular cloud to the west of M17,we expect the hot gas to expand more rapidly to the east;thisflow of hot gas to the east has then blown the blister-like bubble seen in optical images.Four additional point sources are detected in thefield around M17.The brightest of these point sources lies to the south of the X-ray peak and has been previously designated 1WGA J1820.6−1615in the WGA Catalog of ROSAT Point Sources(White,Giommi,& Angelini1994).This point source is coincident with OI352(Ogura&Ishida1976),an O8star on the southern edge of the open cluster in M17.The other three point sources lie on the northern edge of the emission nebula.These X-ray point sources,designated as1WGA J1820.8−1603,1WGA J1821.0−1600,and1WGA J1820.8−1556,are coincident with stars GSC606265−01977,SAO161369(a known O5star),and GSC06265−01808, respectively.These point sources are marked in Figure1a.3.2.X-Ray SpectraIn order to examine the spectra of the diffuse X-ray emission,wefirst excluded the point sources found in§3.1.Then,noting that M17is on the edge of a dense molecular cloud,we have sectioned the nebula into four regions to account for anticipated changes in the foreground absorption column density.These regions have been labeled A,B,C,and D and are displayed in Figure2.Additionally,we have selected a background annulus around the superbubble,as indicated in Figure2.The background-subtracted spectra were then extracted from the PSPC eventfiles.The observed X-ray spectra of the superbubble is a convolution of several factors:the intrinsic X-ray spectrum of the superbubble,the intervening interstellar absorption,and the PSPC response function.Because the interstellar absorption and the PSPC response function are dependent on photon energy,we must assume models of the intrinsic X-ray spectrum and the interstellar absorption to make the problem tractable.As the X-ray emission from the superbubble interior appears largely diffuse,we have used the Raymond &Smith(1977)thermal plasma emission model to describe the intrinsic X-ray spectra of the superbubble and the Morrison&McCammon(1983)effective absorption cross-section per hydrogen atom for the foreground absorption,assuming solar abundances for both the emitting and absorbing materials.We then simulated the observed spectrum,combining theassumed models for the intrinsic spectrum and the interstellar absorption with the responsefunction of the PSPC.The best-fit spectrum is found by varying parameters and comparingχ2for the simulated and observed spectra.We performed aχ2grid search of simulated spectralfits to determine the best-fit levelsfor the thermal plasma temperature,kT,and absorption column density,N H.Plots of thebestfits to the X-ray spectra are shown in Figure3,andχ2plots are presented in Figure4.Theχ2plots of regions A,B,and C indicate that the X-ray emission can befit by eitherhigher temperature plasma,∼0.7keV,with lower absorption column density,∼1020−21cm−2,or lower temperature plasma,∼0.2keV,with higher absorption column density,∼1022cm−2.This is a common problem for PSPC spectra with a limited number of counts because ofthe poor spectral resolution and soft energy coverage of the PSPC.The best modelfits favorthe higher temperature plasma and lower absorption column density solution.Indeed,thedetection of soft X-ray emission below0.5keV indicates that the solution with N H∼1022cm−2cannot be valid,as such a solution predicts no significant soft X-ray emission should bedetected.Furthermore,the high absorption column density solution predicts a foregroundabsorption column density for M17equal to the total Galactic H I column density along theline of sight(Dickey&Lockman1990).As M17is located in the plane of the Galaxy atl=15◦03′,b=−00◦40′and has a distance of1.6kpc,we do not expect the majority of theGalactic H I toward this direction to be located in front of the superbubble.From the modelfits,we calculated the unabsorbed X-rayflux,and therefore the X-rayluminosity,L X,of the diffuse X-ray emission from each source region.The normalizationfactor,A,of the thermal plasma model is equal to n e n p dV/4πD2,where n e and n p are the electron and proton number densities,V is the volume of the superbubble,and D is thedistance to the source.Assuming a He:H number ratio of1:10and that the X-ray emittinggas is completely ionized,wefind n e≃1.2n p,and that the volume emission measure can beexpressed as<n2e>fV,where f is the volumefilling factor.We have used the diameter ofthe superbubble,∼10–12pc,as the depth of the X-ray emitting gas in each source region.We determined the volume,V,of each source region by multiplying the surface area of theregion by the depth and a geometric correction factor of2/3(approximated by the volumeratio of a sphere to a cylinder).Taking the volumefilling factor to be f=0.5,we thencalculated rms n e in each region.The best-fit values of kT,A,N H,L X and rms n e are givenin Table1.Note that the modelfit to region D did not converge because it contains a largenumber of unresolved stellar sources as well as diffuse emission;only approximate values forthe X-ray luminosity and absorption column density are given.See Townsley et al.(2003)for a detailed analysis of the Chandra observations of region D.Combining our results from each of the source regions,wefind a total diffuse X-ray lu-minosity of∼2.5×1033ergs s−1in the ROSAT PSPC0.1–2.4keV band,a mean characteristic temperature of kT∼0.72keV or T∼8.5×106K,a mean electron density of∼0.09cm−3,and a total hot gas mass of∼1M⊙.We have calculated the total thermal energy in hot,shocked wind component of the superbubble to be E th∼1×1048ergs with a cooling timescale of t T∼40Myr.Given the stellar age of the open cluster,∼1Myr,we do not expect significant radiative cooling to have occurred.As a rough check,we multiply the current X-ray lumi-nosity by the age of the cluster andfind that the total energy radiated away by the X-ray emission is 10%of the total thermal energy.4.Discussionparisons with Model ExpectationsWe now compare the observed physical properties of M17determined above to theo-retical calculations from basic wind-blown bubble models.Although the M17superbubble is in an inhomogeneous ambient medium with a significant density gradient and the cluster is off-centered(a more complex scenario than is considered in basic bubble models),if the superbubble structure is indeed governed by the physical processes prescribed by these mod-els,we expect the properties of the diffuse X-ray emission to agree with predictions within similar orders of magnitude.Wefirst consider the wind-blown bubble model of Weaver et al.(1977)and will later consider a wind-blown bubble model without heat conduction.4.1.1.A Bubble with Heat ConductionIn the Weaver et al.model,heat conduction and mass evaporation act across the bound-ary between the hot interior gas and the nebular shell to lower the temperature and raise the density of the bubble interior.The temperature and electron density profiles of such a bubble have been calculated by Weaver et al.(1977),and the X-ray luminosities of such bubbles can be determined using two methods outlined by Chu et al.(1995).In thefirst method,we derive the expected X-ray luminosity from the observed physical properties of the gas in the104K ionized shell of swept-up ISM.In the second method,we use the spectral types of massive stars in M17to estimate the combined mechanical luminosity of the stellar winds and then derive the expected X-ray luminosity.These two methods use independent input parameters and thus allow us to check the consistency of the pressure-driven bubble model in addition to comparing the expected and observed X-ray luminosities.X-Ray Luminosity Method1:The Ionized ShellThe expected X-ray luminosity in the ROSAT band of0.1–2.4keV for the Weaver et al. (1977)wind-blown bubble model has been given by Chu et al.(1995),L X=(8.2×1027ergs s−1)ξI(τ)n10/70R17/7pcV16/7km/s,(1)whereξis the metallicity relative to the solar value and in this case we assume a value of unity,I(τ)is a dimensionless integral of value∼2,n0is the number density of the ambient medium in cm−3,R pc is the radius of the superbubble in pc,V km/s is the expansion velocity of the superbubble in units of km s−1.The ambient density n0cannot be measured directly, but assuming that the ram pressure of the expanding shell is equal to the thermal pressure of the ionized superbubble shell,the relation between the ambient density and the density of the ionized shell is given byn0=(9/7)n i kT i/(µa V2exp),(2) where n i is the electron number density in the ionized shell,T i∼104K is the electron temperature in the ionized shell,V exp is the expansion velocity of the bubble,andµa= (14/11)m H(Weaver et al.1977;Chu&Mac Low1990).Adopting a mean electron density of n i∼300cm−3(Felli,Churchwell,&Massi1984)and an observed V exp∼25km s−1(Clayton et al.1985),we calculated an ambient density of n0∼40cm−3.Given the superbubble radius of5–6pc,we have determined an expected X-ray luminosity of∼3×1035ergs s−1.X-Ray Luminosity Method2:Wind Luminosity from OB StarsWe can also calculate the expected X-ray luminosity in an energy-conserving,wind-blown bubble by the following equation from Chu et al.(1995),L X=(1.1×1035ergs s−1)ξI(τ)L33/3537n17/35t19/35Myr,(3)where L37is the mechanical luminosity of the stellar winds in units of1037ergs s−1,and t Myr is the age of the bubble in Myr.To remain independent of Method1,we do not use the value of n0determined for that method.Rather,we use the following relations between ambient density,radius,wind luminosity,bubble age,and expansion velocity,n0=(1.3×108cm−3)L37t3Myr R−5pc,(4)t Myr=(0.59Myr)R pc/V km/s,(5) (Weaver et al.1977;Chu et al.1995).We again take the expansion velocity to be∼25km s−1 (Clayton et al.1985)and the radius to be5–6pc and derive a bubble age of∼0.13Myr.To determine the wind luminosity of M17,we examined its massive stellar content. Hanson et al.(1997)identified nine O stars and four late-O/early-B stars in the open cluster. Using the spectral types of these massive stars,we have estimated their terminal stellar wind velocities,effective temperatures,and luminosities based on the stellar parameters given by Prinja,Barlow,&Howarth(1990)and Vacca,Garmany,&Shull(1996).We then calculated the mass-loss rates for the OB stars in M17by utilizing the empirically derived relationship between effective temperature,luminosity,and mass-loss rate of de Jager,Nieuwenhuijzen,& van der Hucht(1988).Table2lists the detected OB stars,their spectral types as determined from optical and K-band observations,their terminal wind velocities V∞,stellar effective temperatures T eff,stellar luminosities L,and their mass-loss rates˙M.We calculated the total mechanical luminosity of the stellar winds,L w=Σ(1/2)˙MV2∞,(6) from the OB stars to be∼1×1037ergs s−1.As noted by Felli et al.(1984),the identified OB stars can approximately account for the ionization of the emission nebula;we therefore expect our calculated wind mechanical luminosity to be reasonably complete as well.Assuming a relatively constant mechanical luminosity,wefind a total energy deposited by stellar winds of∼4×1049ergs over the life of the bubble.In addition,this value of the wind mechanical luminosity gives an ambient density of∼60cm−3and an expected X-ray luminosity of ∼5×1035ergs s−1.This X-ray luminosity value is consistent to within a factor of two with the value found by Method1.Although the two methods of determining the expected X-ray luminosity are consistent with each other,they do not agree with the X-ray luminosity derived from the PSPC obser-vation.The observed X-ray luminosity is∼100–200times lower than expected from Weaver et al.’s bubble model.It is possible that stellar winds are clumpy,as suggested by Moffat& Robert(1994),then the conventionally derived mass loss rates would be reduced by a factor of≥3.Even using the reduced mass loss rates,the expected X-ray luminosity is more than 40times too high.The observed temperature,density,and surface brightness of the hot gas in M17do not agree with the model expectations,either.The physical conditions of the shocked stellar winds in Weaver et al.’s model are heavily modified by heat conduction and the hot gas mass is dominated by the nebular mass evaporated across the interface.The predicted temperature is5.0–5.6×106K near the center and decreases outward,the predicted density is0.2–0.4cm−3near the center and increases outward,and the X-ray surface bright-ness is expected to show pared with observed properties,the expected temperature is too low,density is too high,and the X-ray morphology is inconsistent.The disagreements between observations and model expectations suggest that heat conduction may not play a dominant role in determining the physical conditions inside this superbubble.Heat conduction can be suppressed by the presence of magneticfields(Soker1994;Band &Liang1988).The magneticfield strength in M17has been measured via the H I Zeeman effect to be100–550µG,peaking near the interface between the H II region and the molecular cloud M17SW(Brogan et al.1999).Assuming a comparable magneticfield strength in the swept-up104K shell,wefind the Alfv´e n speed to be10–60km s−1which is comparable to or much greater than the isothermal sound velocity of the104K gas,10km s−1for H atoms. In addition,the magneticfield strength and isothermal sound velocity indicate a gyro-radius of 10km for protons in the swept-up shell.This suggests that the protons in the104K gas will be unable to escape the magneticfield and diffuse into the interior of the superbubble, inhibiting heat conduction and mass evaporation between the hot interior and the cool shell of the bubble.4.1.2.A Bubble without Heat ConductionWe now turn our consideration to a wind-blown bubble without heat conduction.The X-ray emission of a bubble interior depends on both the temperature and the amount of hot gas.We willfirst compare the plasma temperature expected from the shocked stellar winds to the observed hot gas ing the combined stellar winds mass-loss rate of 4.3×10−6M⊙yr−1(summed from Table2)and the integrated wind mechanical luminosity L w of1×1037ergs s−1as calculated in§4.1.1,we derive an rms terminal wind velocity of V∞∼2700km s−1.The post-shock temperature of the combined stellar winds is therefore expected to be∼8×107K.This temperature is an order of magnitude higher than that indicated by PSPC observations;to lower it to the observed temperature of∼8.6×106K requires the mixing in of cold nebular mass that is nearly10times the mass of the combined stellar winds.This mixing may be provided by turbulent instabilities at the interface between the shocked fast winds and the cold nebular shell(e.g.,Strickland&Stevens1998)or through the hydronamic ablation of clumps of cold nebular material distributed within the hot bubble interior(Pittard,Hartquist,&Dyson2001).Assuming that mixing has taken place,we next determine the hot gas mass expected as a result of mixing and compare it to the observed value(§3.2).Given the dynamical age of the superbubble,0.13Myr,a total stellar wind mass of∼0.56M⊙has been injected to the superbubble interior,and the expected total mass of the hot gas will be5–6M⊙.This is significantly greater than the observed value of∼1M⊙.This discrepancy can be reduced if we again consider the possibility of clumpy stellar winds(Moffat&Robert1994).With the mass-loss rates reduced by a factor of≥3,the expected hot gas mass is∼2M⊙,which would be in remarkable agreement with the observed value.We summarize the comparison between the observed X-ray emission and the various models in Table3,which lists the observed X-ray luminosity and hot gas temperature and mass as well as those expected from models with and without heat conduction for both homogeneous winds and clumpy winds.It is clear that bubble models with heat conduction have the largest discrepancies from the observations.The best agreement with observed properties is from bubble models without heat conduction but allowing dynamical mixing of cold nebular material with the hot gas.For models either with or without heat conduction, clumpy winds with reduced mass loss rates are needed to minimize the discrepancy between model expectations and observations.parisons with Other Wind-Blown BubblesDiffuse X-ray emission has been previously detected from other types of wind-blown bubbles,including planetary nebulae(PNe)and circumstellar bubbles blown by Wolf-Rayet (WR)stars.The X-ray emission from these circumstellar bubbles is qualitatively and quan-titatively different from that of M17.Chu,Gruendl,&Guerrero(2003)find that the X-ray emission from PNe and WR bubbles shows a limb-brightened spatial distribution,in sharp contrast to the centrally-filled spatial distribution in M17as described in§3.1.Further,Chu et al.(2003)note that PNe and WR bubbles exhibit hot gas temperatures of1–3×106K and electron densities of10–100cm−3,while the hot interior gas of M17exhibits a temperature of8.5×106K and a substantially lower electron density of∼0.09cm−3.The comparisons of morphology and temperature between the M17superbubble and small circumstellar bubbles show fundamental differences.The limb-brightened X-ray spa-tial distribution,low temperatures,and high electron densities of PNe and WR bubbles are qualitatively consistent with a hypothesis of heat conduction and mass evaporation occurring between the hot gas interior and the swept-up shell.However,the observed X-ray luminosi-ties for PNe and WR bubbles are both significantly lower(10–100times)than predicted by bubble models with heat conduction(Chu et al.2001;Wrigge,Wendker,&Wisotzki1994; Wrigge1999).It is possible that in these wind-blown bubbles,heat conduction has also been suppressed and that dynamical mixing,which allows a lower mass injection rate,occurs at the interface between the hot gas interior and the cool nebular shell.Exploring this question will require magneticfield measurements of PNe and WR bubbles.5.SummaryWe have presented analysis of a ROSAT observation of the emission nebula M17.The blister-like morphology seen in the optical images indicates that it is a superbubble blown by the winds of its OB stars in an inhomogeneous ISM.With a stellar age of∼1Myr,M17must be a young quiescent superbubble without any supernova heating.Diffuse X-ray emission is detected from M17and is confined within the optical shell.This suggests the presence of hot106–108K gas in the interior of M17,as is expected in a wind-blown bubble.Analysis of the diffuse X-ray emission indicates a characteristic gas temperature∼8.5×106K with a mean electron number density of0.09cm−3.We have considered bubble models with and without heat conduction and found that those with heat conduction overpredict the X-ray luminosity by two orders of magnitude. Furthermore,the magneticfield measured in M17is large enough to suppress heat conduc-tion and associated mass evaporation.Bubble models without heat conduction overestimate the hot gas temperature unless mixing with cold nebular gas has occurred.If nebular gas can be dynamically mixed into the hot bubble interior and if the stellar winds are clumpy with a lower mass-loss rate,the X-ray morphology and luminosity,and hot gas temperature and mass can be reasonably reproduced.M17provides us a rare opportunity to probe the physical conditions of hot gas energized solely by shocked stellar winds in a quiescent superbubble.While we have learned much from the current analysis,our model considerations were performed on a very basic level.More robust models are needed to accurately describe the evolution of a superbubble in a medium with a large-scale density gradient,small-scale clumpiness,and a strong magneticfield.We would like to thank the anonymous referee for the stimulating comments with have helped us to improve this paper.This research has made use of data obtained through the High Energy Astrophysics Science Archive Research Center Online Service,provided by the NASA/Goddard Space Flight Center.。
211050371_正负压一体式无空气X_射线光电子能谱原位转移仓的开发及研制
第 29 卷第 1 期分析测试技术与仪器Volume 29 Number 1 2023年3月ANALYSIS AND TESTING TECHNOLOGY AND INSTRUMENTS Mar. 2023大型仪器功能开发(30 ~ 36)正负压一体式无空气X射线光电子能谱原位转移仓的开发及研制章小余，赵志娟，袁 震，刘 芬（中国科学院化学研究所，北京 100190）摘要：针对空气敏感材料的表面分析，为了获得更加真实的表面组成与结构信息，需要提供一个可以保护样品从制备完成到分析表征过程中不接触大气环境的装置. 通过使用O圈密封和单向密封柱，提出一种简便且有效的设计概念，自主研制了正负压一体式无空气X射线光电子能谱（XPS）原位转移仓，用于空气敏感材料的XPS测试，利用单向密封柱实现不同工作需求下正负压两种模式的任意切换. 通过对空气敏感的金属Li片和CuCl粉末进行XPS分析表明，采用XPS原位转移仓正压和负压模式均可有效避免样品表面接触空气，保证测试结果准确可靠，而且采用正压密封方式转移样品可以提供更长的密封时效性. 研制的原位转移仓具有设计小巧、操作简便、成本低、密封效果好的特点，适合给有需求的用户开放使用.关键词：空气敏感；X射线光电子能谱；原位转移；正负压一体式中图分类号：O657; O641; TH842 文献标志码：B 文章编号：1006-3757（2023）01-0030-07 DOI：10.16495/j.1006-3757.2023.01.005Development and Research of Inert-Gas/Vacuum Sealing Air-Free In-Situ Transfer Module of X-Ray Photoelectron SpectroscopyZHANG Xiaoyu， ZHAO Zhijuan， YUAN Zhen， LIU Fen（Institute of Chemistry Chinese Academy of Sciences, Beijing 100190, China）Abstract：For the surface analysis of air sensitive materials, and from the sample preparation to characterization, it is necessary to provide a device that can protect samples from exposing to the atmosphere environment so as to obtain accurate and impactful data of the surface chemistry. Through the use of O-ring and one-way sealing, a simple and effective design concept has been demonstrated, and an inert-gas/vacuum sealing air-free X-ray photoelectron spectroscopic (XPS) in-situ transfer module has been developed to realize the XPS analysis of air sensitive materials. The design of one-way sealing was achieved conveniently by switching between inert-gas and vacuum sealing modes in face of different working requirements. The XPS analysis of air-sensitive metal Li sheets and CuCl powders showed that both the sealing modes (an inert-gas/vacuum sealing) of the XPS in-situ transfer module can effectively avoid air contact on the sample surface, and consequently, can ensure the accuracy and reliability of XPS data. Furthmore, the inert gas sealing mode can keep the sample air-free for a longer time. The homemade XPS in-situ transfer module in this work is characterized by a compact design, convenient operation, low cost and effective sealing, which is suitable for the open access to the users who need it.收稿日期：2022−12−07； 修订日期：2023−01−17.基金项目：中国科学院化学研究所仪器孵化项目[Instrument and Device Functional Developing Project of Institute of Chemistry Chinese Academy of Sciences]作者简介：章小余（1986−），女，硕士，工程师，主要研究方向为电子能谱技术及材料表面分析，E-mail：xyiuzhang@ .Key words：air-sensitive；X-ray photoelectron spectroscopy；in-situ transfer；inert-gas/vacuum sealingX射线光电子能谱（XPS）是一种表面灵敏的分析技术，通常用于固体材料表面元素组成和化学态分析[1]. 作为表面分析领域中最有效的方法之一，XPS广泛应用于纳米科学、微电子学、吸附与催化、环境科学、半导体、冶金和材料科学、能源电池及生物医学等诸多领域[2-3]. 其中在催化和能源电池材料分析中，有一些样品比较特殊，比如碱金属电池[4-6]、负载型纳米金属催化剂[7-8]和钙钛矿材料[9]对空气非常敏感，其表面形态和化学组成接触空气后会迅速发生改变，直接影响采集数据的准确性和有效性，因此这类样品的表面分析测试具有一定难度. 目前，常规的光电子能谱仪制样转移过程通常是在大气环境中，将样品固定在标准样品台上，随后放入仪器进样室内抽真空至1×10−6 Pa，再转入分析室内进行测试. 这种制备和进样方式无法避免样品接触大气环境，对于空气敏感材料，其表面很容易与水、氧发生化学反应，导致无法获得材料表面真实的结构信息.为了保证样品表面状态在转移至能谱仪内的过程中不受大气环境影响，研究人员采用了各种技术来保持样品转移过程中隔绝空气. 比如前处理及反应装置与电子能谱仪腔室间真空传输[10-12]、外接手套箱 [13-14]、商用转移仓[15-16]、真空蒸镀惰性金属比如Al层（1.5~6 nm）[17]等. 尽管上述技术手段有效，但也存在一些缺点，例如配套装置体积巨大、试验过程不易操作、投入成本高等，这都不利于在普通实验室内广泛应用. 而一些电子能谱仪器制造商根据自身仪器的特点也研发出了相应配套的商用真空传递仓，例如Thermofisher公司研发的一种XPS 真空转移仓，转移过程中样品处于微正压密封状态，但其价格昂贵，体积较大，转移过程必须通过手套箱大过渡舱辅助，导致传递效率低，单次需消耗至少10 L高纯氩气，因此购置使用者较少，利用率低.另外有一些国内公司也研发了类似的商品化气体保护原位传递仓，采用微正压方式密封转移样品，但需要在能谱仪器进样室舱门的法兰上外接磁耦合机械旋转推拉杆，其操作复杂且放置样品的有效区域小，单次仅可放置尺寸为3 mm×3 mm的样品3～4个，进样和测试效率较低. 因此，从2016年起本实验团队开始自主研制XPS原位样品转移装置[18]，经过结构与性能的迭代优化[19]，最终研制出一种正负压一体式无空气XPS原位转移仓[20]（本文简称XPS原位转移仓），具有结构小巧、操作便捷、成本低、密封效果好、正压和负压密封两种模式转移样品的特点. 为验证装置的密封时效性能，本工作选取两种典型的空气敏感材料进行测试，一种是金属Li材料，其化学性质非常活泼，遇空气后表面迅速与空气中的O2、N2、S等反应导致表面化学状态改变. 另一种是无水CuCl粉末，其在空气中放置短时间内易发生水解和氧化. 试验结果表明，该XPS 原位转移仓对不同类型的空气敏感样品的无空气转移均可以提供更便捷有效的密封保护. 目前，XPS原位转移仓已在多个科研单位的实验室推广使用，支撑应用涉及吸附与催化、能源环境等研究领域.1 试验部分1.1 XPS原位转移仓的研制基于本实验室ESCALAB 250Xi型多功能光电子能谱仪器（Thermofisher 公司）的特点，研究人员设计了XPS原位转移仓. 为兼顾各个部件强度、精度与轻量化的要求，所有部件均采用钛合金材料.该装置从整体结构上分为样品台、密封罩和紧固挡板三个部件，如图1（a）~（c）所示. 在密封罩内部通过单向密封设计[图1（e）]使得XPS原位转移仓实现正负压一体，实际操作中可通过调节密封罩上的螺帽完成两种模式任意切换. 同时，从图1（e）中可以直观看到，密封罩与样品台之间通过O圈密封，利用带有螺钉的紧固挡板将二者紧密固定. 此外，为确保样品台与密封罩对接方位正确，本设计使用定向槽定位样品台与密封罩位置，保证XPS原位转移仓顺利传接到仪器进样室.XPS原位转移仓使用的具体流程：在手套箱中将空气敏感样品粘贴至样品台上，利用紧固挡板使样品台和密封罩固定在一起，通过调节密封罩上的螺帽将样品所在区域密封为正压惰性气氛（压强为300 Pa、环境气氛与手套箱内相同）或者负压真空状态，其整体装配实物图如图1（d）所示. 该转移仓结构小巧，整体尺寸仅52 mm×58 mm×60 mm，可直接放入手套箱小过渡舱传递. 由于转移仓尺寸小，其第 1 期章小余，等：正负压一体式无空气X射线光电子能谱原位转移仓的开发及研制31原料成本大大缩减，整体造价不高. 转移仓送至能谱仪进样室后，配合样品停放台与进样杆的同时双向对接，将转移仓整体固定在进样室内，如图1（f ）所示. 此时关闭进样室舱门开始抽真空，当样品台与密封罩内外压强平衡后密封罩自动解除真空密封，但仍然处于O 圈密闭状态. 等待进样室真空抽至1×10−4Pa 后，使用能谱仪进样室的样品停放台摘除脱离的密封罩[如图1（g ）所示]，待真空抽至1×10−6Pa ，即可将样品送入分析室进行XPS 测试.整个试验过程操作便捷，实现了样品从手套箱转移至能谱仪内不接触大气环境.1.2 试验过程1.2.1 样品准备及转移试验所用手套箱是布劳恩惰性气体系统（上海）有限公司生产，型号为MB200MOD （1500/780）NAC ；金属Li 片购自中能锂业，纯度99.9%；CuCl 购自ALFA 公司，纯度99.999%.金属Li 片的制备及转移：将XPS 原位转移仓整体通过手套箱过渡舱送入手套箱中，剪取金属Li 片用双面胶带固定于样品台上，分别采用正压、负压两种密封模式将XPS 原位转移仓整体从手套箱中取出，分别在空气中放置0、2、4、8、18、24、48、72 h 后送入能谱仪内，进行XPS 测试.CuCl 粉末的制备及转移：在手套箱中将CuCl 粉末压片[21]，使用上述同样的制备方法，将XPS 原位转移仓整体在空气中分别放置0、7、24、72 h 后送入能谱仪内，进行XPS 测试.1.2.2 样品转移方式介绍样品在手套箱中粘贴完成后，分别采用三种方式将其送入能谱仪. 第一种方式是在手套箱内使用标准样品台粘贴样品，将其装入自封袋密封，待能谱仪进样室舱门打开后，即刻打开封口袋送入仪器中开始抽真空等待测试，整个转移过程中样品暴露空气约15 s. 第二种方式是使用XPS 原位转移仓负压密封模式转移样品，具体操作步骤：利用紧固挡板将样品台和密封罩固定在一起，逆时针（OPEN ）旋动螺帽至顶部，放入手套箱过渡舱并将其抽为真空，此过程中样品所在区域也抽至负压. 取出整体装置后再顺时针（CLOSE ）旋动螺帽至底部，将样品所在区域进一步锁死密封. 样品在负压环境中转移至XPS 实验室，拆卸掉紧固挡板，随即送入能谱仪进样室内. 第三种方式是使用XPS 原位转移仓正压密封模式转移样品，具体操作步骤：利用紧固挡板将样品台和密封罩固定在一起，顺时针（CLOSE ）旋螺帽抽气管限位板单向密封柱密封罩主体O 圈样品台紧固挡板(e) 密封罩对接停放台机械手样品台对接进样杆(a)(b)(c)(d)(g)图1 正负压一体式无空气XPS 原位转移仓系统装置（a ）样品台，（b ）密封罩，（c ）紧固挡板，（d ）整体装配实物图，（e ）整体装置分解示意图，（f ）样品台与密封罩在进样室内对接完成，（g ）样品台与密封罩在进样室内分离Fig. 1 System device of inert-gas/vacuum sealing air-free XPS in-situ transfer module32分析测试技术与仪器第 29 卷动螺帽至底部，此时样品所在区域密封为正压惰性气氛. 直至样品转移至XPS 实验室，再使用配套真空抽气系统（如图2所示），通过抽气管将样品所在区域迅速抽为负压，拆卸掉紧固挡板，随即送入能谱仪进样室内.图2 能谱仪实验室内配套真空抽气系统Fig. 2 Vacuum pumping system in XPSlaboratory1.2.3 XPS 分析测试试验所用仪器为Thermo Fisher Scientific 公司的ESCALAB 250Xi 型多功能X 射线光电子能谱仪，仪器分析室基础真空为1×10−7Pa ，X 射线激发源为单色化Al 靶（Alk α，1 486.6 eV ），功率150 W ，高分辨谱图在30 eV 的通能及0.05 eV 的步长等测试条件下获得，并以烃类碳C 1s 为284.8 eV 的结合能为能量标准进行荷电校正.2 结果与讨论2.1 测试结果分析为了验证XPS 原位转移仓的密封性能，本文做了一系列的对照试验，选取空气敏感的金属Li 片和CuCl 粉末样品进行XPS 测试，分别采用上述三种方式转移样品，并考察了XPS 原位转移仓密封状态下在空气中放置不同时间后对样品测试结果的影响.2.1.1 负压密封模式下XPS 原位转移仓对金属Li片的密封时效性验证将金属Li 片通过两种（标准和负压密封）方式转移并在空气中放置不同时间，对这一系列样品进行XPS 测试，Li 1s 和C 1s 高分辨谱图结果如图3（a ）（b ）所示，试验所测得的Li 1s 半峰宽值如表1所列. 根据XPS 结果分析，金属Li 片采用标准样品台进样（封口袋密封），短暂暴露空气约15 s ，此时Li 1s 的半峰宽为1.62 eV. 而采用XPS 原位转移仓负压密封模式转移样品时，装置整体放置空气18 h 内，Li 1s 的半峰宽基本保持为（1.35±0.03） eV. 放置空气24 h 后，Li 1s 的半峰宽增加到与暴露空气15 s 的金属Li 片一样，说明此时原位转移仓的密封性能衰减，金属Li 片与渗入内部的空气发生反应生成新物质导致Li 1s 半峰宽变宽. 由图3（b ）中C 1s 高分辨谱图分析，结合能位于284.82 eV 的峰归属为C-C/污染C ，位于286.23 eV 的峰归属为C-OH/C-O-CBinding energy/eVI n t e n s i t y /a .u .Li 1s半峰宽增大暴露 15 s密封放置 24 h 密封放置 18 h 密封放置 8 h 密封放置 4 h 密封放置 0 h6058565452Binding energy/eVI n t e n s i t y /a .u .C 1s(a)(b)暴露 1 min 暴露 15 s 密封放置 24 h 密封放置 18 h 密封放置 0 h292290288284282286280图3 金属Li 片通过两种（标准和负压密封）方式转移并在空气中放置不同时间的（a ）Li 1s 和（b ）C 1s 高分辨谱图Fig. 3 High-resolution spectra of (a) Li 1s and (b) C 1s of Li sheet samples transferred by two methods (standard andvacuum sealings) and placed in air for different times第 1 期章小余，等：正负压一体式无空气X 射线光电子能谱原位转移仓的开发及研制33键，位于288.61~289.72 eV的峰归属为HCO3−/CO32−中的C[22]. 我们从C 1s的XPS谱图可以直观的看到，与空气短暂接触后，样品表面瞬间生成新的结构，随着暴露时间增加到1 min，副反应产物大量增加（HCO3−/CO32−）. 而XPS原位转移仓负压密封模式下在空气中放置18 h内，C结构基本不变，在空气中放置24 h后，C结构只有微小变化. 因此根据试验结果分析，对于空气极其敏感的材料，在负压密封模式下，建议XPS原位转移仓在空气中放置时间不要超过18 h. 这种模式适合对空气极其敏感样品的短距离转移.表 1 通过两种（标准和负压密封）方式转移并在空气中放置不同时间的Li 1s的半峰宽Table 1 Full width at half maxima (FWHM) of Li 1stransferred by two methods (standard and vacuum sealings) and placed in air for different times样品说明进样方式半峰宽/eV密封放置0 h XPS原位转移仓负压密封模式转移1.38密封放置2 h同上 1.39密封放置4 h同上 1.36密封放置8 h同上 1.32密封放置18 h同上 1.32密封放置24 h同上 1.62暴露15 s标准样品台进样（封口袋密封）1.622.1.2 正压密封模式下原位转移仓对金属Li片的密封时效性验证将金属Li片通过两种（标准和正压密封）方式转移并在空气中放置不同时间，对这一系列样品进行XPS测试，Li 1s高分辨谱图结果如图4所示，所测得的Li 1s半峰宽值如表2所列. 根据XPS结果分析，XPS原位转移仓正压密封后，在空气中放置72 h内，Li 1s半峰宽基本保持为（1.38±0.04） eV，说明有明显的密封效果，金属Li片仍然保持原有化学状态. 所以对于空气极其敏感的材料，在正压密封模式下，可至少在72 h内保持样品表面不发生化学态变化. 这种模式适合长时间远距离（可全国范围内）转移空气敏感样品.2.1.3 负压密封模式下XPS原位转移仓对空气敏感样品CuCl的密封时效性验证除了金属Li片样品，本文还继续考察XPS原位转移仓对空气敏感样品CuCl的密封时效性. 图5为CuCl粉末通过两种（标准和负压密封）方式转移并在空气中放置不同时间的Cu 2p高分辨谱图. XPS谱图中结合能[22]位于932.32 eV的峰归属为Cu+的Cu 2p3/2，位于935.25 eV的峰归属为Cu2+的Cu 2p3/2，此外，XPS谱图中位于940.00~947.50 eV 处的峰为Cu2+的震激伴峰，这些震激伴峰被认为是表 2 通过两种（标准和正压密封）方式转移并在空气中放置不同时间的Li 1s的半峰宽Table 2 FWHM of Li 1s transferred by two methods(standard and inert gas sealings) and placed in air fordifferent times样品说明进样方式半峰宽/eV 密封放置0 h XPS原位转移仓正压密封模式转移1.42密封放置2 h同上 1.35密封放置4 h同上 1.35密封放置8 h同上 1.34密封放置18 h同上 1.38密封放置24 h同上 1.39密封放置48 h同上 1.42密封放置72 h同上 1.38暴露15 s标准样品台进样（封口袋密封）1.62Binding energy/eVIntensity/a.u.Li 1s半峰宽比正压密封的宽半峰宽=1.62 eV半峰宽=1.38 eV暴露 15 s密封放置 72 h密封放置 48 h密封放置 24 h密封放置 18 h密封放置 0 h605856545250图4 金属Li片通过两种（标准和正压密封）方式转移并在空气中放置不同时间的Li 1s高分辨谱图Fig. 4 High-resolution spectra of Li 1s on Li sheet samples transferred by two methods (standard and inert gas sealings) and placed in air for different times34分析测试技术与仪器第 29 卷价壳层电子向激发态跃迁的终态效应所产生[23]，而在Cu +和Cu 0中则观察不到.根据XPS 结果分析，CuCl 在XPS 原位转移仓保护（负压密封）下，即使放置空气中72 h ，测得的Cu 2p 高分辨能谱图显示只有Cu +存在，说明CuCl 并未被氧化. 若无XPS 原位转移仓保护，CuCl 粉末放置空气中3 min 就发生了比较明显的氧化，从测得的Cu 2p 高分辨能谱图能够直观的看到Cu 2+及其震激伴峰的存在，并且随着放置时间增加到40 min ，其氧化程度也大大增加. 因此，对于空气敏感的无机材料、纳米催化剂和钙钛矿材料等，采用负压密封模式转移就可至少在72 h 内保持样品表面不发生化学态变化.3 结论本工作中自主研制的正负压一体式无空气XPS原位转移仓在空气敏感样品转移过程中可以有效隔绝空气，从而获得样品最真实的表面化学结构.试验者可根据样品情况和实验室条件选择转移模式，并在密封有效时间内将样品从实验室转移至能谱仪中完成测试. 综上所述，该XPS 原位转移仓是一种设计小巧、操作简便、密封性能优异、成本较低的样品无水无氧转移装置，因此非常适合广泛开放给有需求的试验者使用. 在原位和准原位表征技术被广泛用于助力新材料发展的现阶段，希望该设计理念能对仪器功能的开发和更多准原位表征测试的扩展提供一些启示.参考文献：黄惠忠. 论表面分析及其在材料研究中的应用[M ].北京: 科学技术文献出版社, 2002: 16-18.［ 1 ］杨文超, 刘殿方, 高欣, 等. X 射线光电子能谱应用综述[J ]. 中国口岸科学技术，2022，4（2）：30-37.[YANG Wenchao, LIU Dianfang, GAO Xin, et al.TheapplicationofX -rayphotoelectronspectroscopy [J ]. China Port Science and Technology ，2022，4 （2）：30-37.]［ 2 ］郭沁林. X 射线光电子能谱[J ]. 物理，2007，36（5）：405-410. [GUO Qinlin. X -ray photoelectron spectro-scopy [J ]. Physics ，2007，36 （5）：405-410.]［ 3 ］Malmgren S, Ciosek K, Lindblad R, et al. Con-sequences of air exposure on the lithiated graphite SEI [J ]. Electrochimica Acta ，2013，105 ：83-91.［ 4 ］Zhang Y H, Chen S M, Chen Y, et al. Functional poly-ethylene glycol-based solid electrolytes with enhanced interfacial compatibility for room-temperature lithium metal batteries [J ]. Materials Chemistry Frontiers ，2021，5 （9）：3681-3691.［ 5 ］周逸凡, 杨慕紫, 佘峰权, 等. X 射线光电子能谱在固态锂离子电池界面研究中的应用[J ]. 物理学报，2021，70（17）：178801. [ZHOU Yifan, YANG Muzi,SHE Fengquan, et al. Application of X -ray photoelec-tron spectroscopy to study interfaces for solid-state lithium ion battery [J ]. Acta Physica Sinica ，2021，70（17）：178801.]［ 6 ］Huang J J, Song Y Y, Ma D D, et al. The effect of thesupport on the surface composition of PtCu alloy nanocatalysts: in situ XPS and HS-LEIS studies [J ].Chinese Journal of Catalysis ，2017，38 （7）：1229-1236.［ 7 ］Koley P, Shit S C, Sabri Y M, et al. Looking into moreeyes combining in situ spectroscopy in catalytic bio-fuel upgradation with composition-graded Ag-Co core-shell nanoalloys [J ]. ACS Sustainable Chemistry &Engineering ，2021，9 （10）：3750-3767.［ 8 ］Opitz A K, Nenning A, Rameshan C, et al. Enhancingelectrochemical water-splitting kinetics by polarization-driven formation of near-surface iron(0): an in situ XPS study on perovskite-type electrodes [J ]. Ange-wandte Chemie (International Ed in English)，2015，54（9）：2628-2632.［ 9 ］Czekaj I, Loviat F, Raimondi F, et al. Characterization［ 10 ］Binding energy/eVI n t e n s i t y /a .u .Cu 2pCu +Cu 2+暴露 3 min暴露 40 min 密封放置 7 h 密封放置 72 h 密封放置 24 h密封放置 0 h960950945935925955940930920图5 CuCl 粉末通过两种（标准和负压密封）方式转移并在空气中放置不同时间的Cu 2p 高分辨谱图Fig. 5 High-resolution spectra of Cu 2p on CuCl powder samples transferred by two methods (standard and vacuumsealings) and placed in air for different times第 1 期章小余，等：正负压一体式无空气X 射线光电子能谱原位转移仓的开发及研制35of surface processes at the Ni-based catalyst during the methanation of biomass-derived synthesis gas: X -ray photoelectron spectroscopy (XPS)[J ]. Applied Cata-lysis A:General ，2007，329 ：68-78.Rutkowski M M, McNicholas K M, Zeng Z Q, et al.Design of an ultrahigh vacuum transfer mechanism to interconnect an oxide molecular beam epitaxy growth chamber and an X -ray photoemission spectroscopy analysis system [J ]. Review of Scientific Instruments ，2013，84 （6）：065105.［ 11 ］伊晓东, 郭建平, 孙海珍, 等. X 射线光电子能谱仪样品前处理装置的设计及应用[J ]. 分析仪器，2008（5）：8-11. [YI Xiaodong, GUO Jianping, SUN Haizhen, et al. Design of a sample pretreatment device for X -ray photoelectron spectrometer [J ]. Analytical Instrumentation ，2008 （5）：8-11.]［ 12 ］Aurbach D, Weissman I, Schechter A, et al. X -ray pho-toelectron spectroscopy studies of lithium surfaces pre-pared in several important electrolyte solutions. A comparison with previous studies by Fourier trans-form infrared spectroscopy [J ]. Langmuir ，1996，12（16）：3991-4007.［ 13 ］Światowska-Mrowiecka J, Maurice V, Zanna S, et al.XPS study of Li ion intercalation in V 2O 5 thin films prepared by thermal oxidation of vanadium metal [J ].Electrochimica Acta ，2007，52 （18）：5644-5653.［ 14 ］Weingarth D, Foelske-Schmitz A, Wokaun A, et al. Insitu electrochemical XPS study of the Pt/[BF 4]system [J ]. Electrochemistry Communications ，2011，13 （6）：619-622.［ 15 ］Schneider J D, Agocs D B, Prieto A L. Design of asample transfer holder to enable air-free X -ray photo-electron spectroscopy [J ]. Chemistry of Materials ，2020，32 （19）：8091-8096.［ 16 ］Karamurzov B S, Kochur A G, Misakova L B, et al.Calculation of the pure surface composition of the bin-ary alloy according to XPS data obtained after the al-loy surface contact with air [J ]. Journal of Structural Chemistry ，2015，56 （3）：576-581.［ 17 ］章小余, 赵志娟. 一种半原位XPS 样品转移装置: 中国, 201620925237.5[P ]. 2017-02-15.［ 18 ］章小余, 袁震, 赵志娟. 一种半原位X 射线光电子能谱分析仪的样品转移装置: 中国, 201720056623.X [P ]. 2017-12-08.［ 19 ］袁震, 章小余, 赵志娟. 一种样品转移装置及转移方法: 中国, 2011203822.1[P ]. 2022-03-01.［ 20 ］刘芬, 赵志娟, 邱丽美, 等. XPS 分析固体粉末时的样品制备法研究[J ]. 分析测试技术与仪器，2007，13（2）：107-109. [LIU Fen, ZHAO Zhijuan, QIU Limei, et al. Study of sample preparation method for XPS analysis of powdered samples [J ]. Analysis and Testing Technology and Instruments ，2007，13 （2）：107-109.]［ 21 ］Wagner C D, Riggs W M, Davis L E, et al. Handbookof X -ray photoelectron spectroscopy [M ]. Eden Prair-ie, Minnesota, 1978.［ 22 ］Watts J F, Wolstenholme J. 表面分析(XPS 和AES)引论[M ]. 吴正龙, 译. 上海: 华东理工大学出版社,2008.［ 23 ］36分析测试技术与仪器第 29 卷。
200611-DIVING-PAM中文操作手册
DIVING-PAM 操作手册
泽泉科技有限公司，德国 WALZ 公司中国技术服务中心
目录
1 安全指导 ...................................................................................................................................- 4 1.1 一般安全指导 ................................................................................................................- 4 1.2 特殊安全指导 ................................................................................................................- 4 -
水下调制荧光仪——
DIVING-PAM
操作手册
2006 年 11 月版
泽泉国际集团（香港）有限公司 泽泉科技有限公司 德 国 WA L Z 公 司 中 国 技 术 服 务 中 心
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传真：010-62304952 转 20
9.1.1 荧光的激发与检测............................................................................................- 28 9.1.2 内置卤素灯 .......................................................................................................- 29 9.1.3 可充电电池 .......................................................................................................- 29 9.1.4 显示器 ...............................................................................................................- 30 9.1.5 电子元件 ...........................................................................................................- 30 9.1.6 接口介绍 ...........................................................................................................- 30 9.2 标准光纤 DIVING-PAM/F 和微光纤 DIVING-PAM/F1 ...........................................- 32 9.3 光量子传感器 ..............................................................................................................- 32 9.4 深度传感器 ..................................................................................................................- 33 9.5 水温传感器 ..................................................................................................................- 33 9.6 水下通用样品架 DIVING-USH ..................................................................................- 33 9.6.1 介绍 ...................................................................................................................- 33 -
三种常见原生动物对褐潮藻种抑食金球藻(Aureococcus anophagefferens)的摄食
三种常见原生动物对褐潮藻种抑食金球藻(Aureococcusanophagefferens)的摄食陈瑶;杨茜露;何学佳【摘要】微型浮游动物在抑食金球藻(Aureococcus anophagefferens)引发褐潮时表现的摄食压力可潜在控制褐潮的爆发和消亡.本研究就三种海洋常见原生动物——海洋尖尾藻(Oxyrrhis marina)、海洋尾丝虫(Uronema marinum)和扇形游仆虫(Euplotes vannus)——对单种饵料及混合饵料中抑食金球藻中国株的摄食进行了研究.单种抑食金球藻指数期细胞喂食的三种原生动物的生长率和摄食率呈现米氏方程变化趋势.比较三种原生动物摄食抑食金球藻的最大摄食率,发现其随动物粒径的增大而增大,但仅为摄食球等鞭金藻(Isochrysis galbana)的30％～59％.海洋尖尾藻和海洋尾丝虫的最大生长率(μmax)与饵料种类无关,扇形游仆虫摄食抑食金球藻时的μmax值小于摄食球等鞭金藻的个体.海洋尖尾藻、海洋尾丝虫和扇形游仆虫摄食抑食金球藻时的毛生长率(gross growth efficiency,GGE)分别为65.8％、35.2％和49.1％.三种原生动物摄食抑食金球藻指数期细胞和球等鞭金藻以不同比例混合的饵料时表现出对抑食金球藻的选择倾向;在含有抑食金球藻稳定期细胞的混合饵料喂食的情况下,三种原生动物避食抑食金球藻或不表现明显摄食倾向性.抑食金球藻释放胞外聚合物(extracellular polymeric substance,EPS)的测定结果显示,细胞从指数期生长至稳定期释放出的EPS的水平显著上升(P<0.05),可能与原生动物对不同生长期藻细胞具有不同选择偏好有关.【期刊名称】《热带海洋学报》【年(卷),期】2018(037)006【总页数】13页(P120-132)【关键词】褐潮;抑食金球藻;原生动物;摄食;EPS【作者】陈瑶;杨茜露;何学佳【作者单位】暨南大学赤潮与海洋生物学研究中心,水体富营养化与赤潮防治广东普通高校重点实验室,广东广州 510632;暨南大学赤潮与海洋生物学研究中心,水体富营养化与赤潮防治广东普通高校重点实验室,广东广州 510632;暨南大学赤潮与海洋生物学研究中心,水体富营养化与赤潮防治广东普通高校重点实验室,广东广州510632【正文语种】中文【中图分类】Q178.53;Q958.12+2.2抑食金球藻(Aureococcus anophagefferens)是引发褐潮的主要原因种之一, 其引发的褐潮在美国和南非等地持续了20年之久(Bricelj et al, 1997; Probyn et al, 2001; Deonarine et al, 2006)。
Unit 5.Force of nature. ppt
Louis Pasteur Some of his works are: separation of mirror image molecules and effect of polarized light identification of the parasite that was killing silkworms James Maxwell He is known for the "Treatise on Electricity and Magnetism" published in 1873. Maxwell independently developed the "Maxwell-Boltzmann kinetic theory of gases". Edwin Hubble "Hubble's Law" stated that galaxies move away from each other at a speed determined by the distance that separated them. He classified galaxies as per their distance, shape, brightness patterns and content. Paul Dirac He received a Nobel prize in 1933 for the work on antiparticles. The "Dirac equation" was a version of the Schrodinger's equation.
Barbara Goldsmith is a noted author, historian. Her best-selling books include The Straw Man, Little Gloria…Happy at Last, Johnson v. Johnson, and Other Powers: The Age of Suffrage, Spiritualism, and the Scandalous Victoria Woodhull (soon to be a major motion picture produced by Kathleen Kennedy for Universal Studios) and Obsessive Genius: The Inner World of Marie Curie. Barbara Goldsmith has long been at the forefront of the effort to preserve our written heritage. She is the donor of the Goldsmith Conservation and Preservation Laboratories at the New Yse Divisions were recently named in her honor.
The nature of the luminous X-ray emission of NGC 6240
a r X i v :a s t r o -p h /9902313v 1 22 F eb 1999THE NATURE OF THE LUMINOUS X-RAY EMISSION OF NGC 6240STEFANIE KOMOSSA Max-Planck-Institut f¨u r extraterrestrische Physik,Postfach 1603,D-85740Garching,Germany;skomossa@xray.mpe.mpg.de AND HARTMUT SCHULZ Astronomisches Institut der Ruhr-Universit¨a t,D-44780Bochum,Germany 1.Abstract We briefly review and extend our discussion of the ROSAT detection of the extraordinarily luminous (>1042erg/s)partly extended (>30kpc diam-eter)X-ray emission from the ultraluminous infrared galaxy NGC 6240.The ‘standard’-model of starburst outflow is contrasted with alternatives and a comparison with the X-ray properties of ellipticals is performed.2.Introduction The double-nucleus galaxy NGC 6240is outstanding in several respects:its infrared H 22.121µm and [FeII]1.644µm line luminosities and the ratio of H 2to bolometric luminosities are the largest currently known (van derWerf et al.1993).Its huge far-infrared luminosity of ∼1012L ⊙(Wright et al.1984)comprises nearly all of its bolometric luminosity.Hence,owing to its low redshift of z =0.024,NGC 6240is one of the nearest members of the class of ultraluminous infrared galaxies (hereafter ULIRGs).1Its optical morphology (e.g.,Zwicky et al.1961,Fried &Schulz 1983)and its large stellar velocity dispersion of 360km/s (among the highest values ever found in the center of a galaxy:e.g.,Doyon et al.1994)suggest that it is a1We continue to refer to NGC 6240as ULIRG but note that,owing to the method to integrate over the IRAS bands and the adopted value of H 0,most authors now attribute an IR luminosity <1012L ⊙to NGC 6240rendering it a LIRG instead of a ULIRG2STEFANIE KOMOSSA AND HARTMUT SCHULZmerging system on its way to become an elliptical.Like other ULIRGs,the object contains a compact,luminous CO(1-0)emitting core of molecular gas(Solomon et al.1997).Within this core most of the ultimate power source of the FIR radiation appears to be hidden.There is now growing evidence that LIRGs are predominantly powered by star-formation and that the AGN contribution increases with FIR lu-minosity(e.g.,Shier et al.1996,Lutz et al.1998a,Rigopolou et al.1998; see Sanders&Mirabel1996and Genzel et al.1998for recent reviews) while essentially all of the HyLIRGs contain QSOs(e.g.,Hines et al.1995 and these proceedings).In the‘transition region’around L FIR≃1012L⊙it then requires a careful object-by-object analysis tofind out the majour power source.Concerning NGC6240,at least four scenarios have been sug-gested:Heating of dust by a superluminous starburst,by an AGN,by an old stellar population,and by UV radiation from molecular cloud colli-sions.In particular,previous hints for an AGN included(i)the strength of NIR recombination lines(de Poy et al.1986,depending on the applied reddening correction,though),(ii)the presence of compact bright radio cores(Carral et al.1990but see Colbert et al.1994),(iii)the discovery of a high-excitation core in the southern nucleus with HST(Barbieri et al.1994, 1995,Rafanelli et al.1997),and the detection of the[OIV]25.9µm emission line with ISO(Lutz et al.1996–but see Lutz et al.1998b who discovered this line in a number of starburst galaxies;Egami,this meeting).X-rays are a powerful tool to investigate both,the presence of an AGN and starburst-superwind activity.It is the aim of the present contribution to review briefly and discuss ourfindings of evidence for a hard X-ray component in the ROSAT PSPC spectrum of NGC6240(Schulz et al.1998, SKBB hereafter)and the detection of luminous extended emission based on ROSAT HRI data(Komossa et al.1998)in combination with the discovery of an FeK line and hard X-ray component by ASCA(first reported by Mitsuda1995).Luminosities given below were calculated using H0=50km/s/Mpc. 3.Scenarios to explain the luminous X-ray emission of NGC6240 3.1.SPECTRAL PROPERTIES AND ORIGIN OF THE HARD COMPONENTIn our analysis of ROSAT PSPC data of NGC6240we tested a large vari-ety of models to explain the X-ray spectrum(SKBB).One-componentfits turned out to be unlikely.E.g.,a single Raymond-Smith model requires a huge absorbing column along the line-of-sight,the consequence being an intrinsic(absorption corrected)luminosity of L X,0.1−2.4≃41043erg/s, almost impossible to reach in any starburst-superwind scenario.The oneNATURE OF THE LUMINOUS X-RAY EMISSION OF NGC 62403-173.38170.686171.36-172.706Figure 1.ROSAT HRI X-ray contours showing the presence of luminous extended emission overlaid on an optical image of NGC 6240.The lowest contour is at ∼2σabove the background.model that does not require excess absorption is a single black body.Al-though physically implausible,this description does allow to derive a lower limit on the intrinsically emitted X-ray luminosity which any model has to explain:L X ∼>2.51042erg/s in the (0.1-2.4)keV band (Fricke &Pa-paderos 1996obtained 3.81042erg/s by fitting a thermal bremsstrahlung model and allowing for some excess absorption).Successful two-component models require the presence of a hard X-ray component,in form of either very hot thermal emission (kT ≃7keV)or a powerlaw.2Due to its large luminosity of several 1042erg/s we interpret the hard component to arise from an AGN.Both,the essential lack of non-X-ray evidence for an unobscured AGN,and the high equivalent width of the FeK2The requirement of a second component in the ROSAT band can be omitted if strongly depleted metal abundances are allowed for.This has been reported for other objects as well and the low inferred X-ray abundances are quite puzzling given that other methods yield much higher abundances (as also stressed by Netzer at this meeting).A recent discussion of this issue is given in Komossa &Schulz (1998)and Buote &Fabian (1998)who give arguments in favour of two-component X-ray spectral models of ∼solar abundances in the Raymond-Smith component instead of single-component models of very subsolar abundances.In particular,Buote &Fabian conclude that the necessity of a second X-ray component cannot be circumvented by details of the modelling of the Fe L emission.4STEFANIE KOMOSSA AND HARTMUT SCHULZof NGC6240diagram,comparedof elliptical galax-Canizares et al.1987,&Bregman1998);ellipticals areenviron-circle gives the(0.1-2.4keV)of NGC6240,theone for the favouredmodel(Sect. 3.1;row of their Tab.triangle correspondsL x from HeckmanB was calculated us-in NED.line observed by ASCA(e.g.,Mitsuda et al.1995)suggest we see the AGN mainly in scattered light.Indeed,the X-ray spectrum can be successfully described by a‘warm scatterer’(cf.Fig.4of Komossa et al.1998),highly ionized material seen in reflection which could also explain the strong FeK line seen by ASCA.Our model,which was suggested to explain the hard component,is quite similar to the one suggested by Netzer et al.(1998) who,however,explained the whole ASCA spectrum in terms of scattering. In this respect,we emphasize that the widely extended X-ray component detected with the ROSAT HRI(Komossa et al.1998;cf.next Sect.)is likely of different origin,given the low efficiency of a hugely extended scattering mirror(SKBB).With an X-ray luminosity in scattered emission of a few1042erg/s one obtains an intrinsic luminosity of order1044−45erg/s,depending on the covering factor of the scatterer.Variousfits of ASCA spectra(e.g.,Mit-suda1995,Kii et al.1997,Iwasawa1998,Netzer et al.1998,Nakagawa, these proceedings)revealing the extension of the hard component up to10 keV support this conclusion;the various approaches differ in the descrip-tion of the soft component(s)and the amount of absorption of the hard component,though.In any case,the AGN contributes an appreciable frac-tion of the total L bol(NGC6240)=41045erg/s.If L bol(AGN)≃L Edd a black hole mass of M bh≃107M⊙results.NGC6240is expected to form an L∗elliptical galaxy rather than a giant elliptical after having completed its merging epoch(Shier&Fischer1997).However,to match the relation M bh≈0.002M gal(Lauer et al.1997)for the evolved elliptical the black hole has still to grow by an order of magnitude which would require anotherNATURE OF THE LUMINOUS X-RAY EMISSION OF NGC62405 109yrs of accretion while the merger is settling down.Alternatively,the present accretion rate could be below the Eddington rate.The inferred X-ray luminosity is an appreciable fraction of the FIR luminosity,suggesting that both,the starburst(e.g.,Lutz et al.1996)and the AGN power the FIR emission of this ULIRG.3.2.EXTENDED EMISSIONThe HRI images(Komossa et al.1998)reveal that part of the huge X-ray luminosity arises in a roughly spherical source with strong(≥2σabove background)emission out to a radius of20′′(∼14kpc;Fig.1).Hence, NGC6240is the host of one of the most luminous extended X-ray sources in isolated galaxies(see Fig.2where L X is compared with a sample of elliptical galaxies and Arp220).Analytical estimates based on the Mac Low &McCray(1988)models show that the extended emission can be explained by superwind-shell interaction from the central starburst(SKBB).A puzzle is the high circular symmetry of the X-ray bubble,in contrast to the bicone-symmetry expected in a wind-driven supershell scenario so that it seems worthwhile to look for further potential contributors to the X-ray emission.An additional small contribution may come from a wind induced by the large velocity dispersion of350km/s(Lester&Gaffney1994)leading to shocks in the gas expelled by the red giant population.Another inter-esting point is that the extended X-ray bubbles around elliptical galaxies are usually brighter in the inflow phases or‘when caught in the verge of experiencing their central cooling catastrophe’(Ciotti et al.1991,Friaca &Terlevich1998).Although time scales and details for an ongoing merger are certainly different,it is conceivable that NGC6240experiences a lack of heating when a majour starburst period has ended.In this case,a cooling flow would commence boosting L x and presumably shock heating the ISM in the central kiloparsecs.Due to fragmentation,shock velocities could be enhanced causing the LINER like line ratios in the two nuclei(gravitational centers)and,with lower velocities,excite the molecular cloud complex be-tween the nuclei leading to the extreme H2luminosity found there(van der Werf et al.1993).Its exceptional X-ray properties make NGC6240a prime target for fu-ture X-ray satellites like XMM and AXAF.AcknowledgementsSt.K.acknowledges support from the Verbundforschung under grant No. 50OR93065and thanks the organizers for the very efficient workshop and the pleasant workshop atmosphere.6STEFANIE KOMOSSA AND HARTMUT SCHULZ ReferencesBarbieri C.,Rafanelli P.,Schulz H.,Komossa S.,1994,Astron.Ges.Abstr.Ser.10,217 Barbieri C.,Rafanelli P.,Schulz H.,Komossa S.,Baruffolo A.,1995,in17th Texas Symp.on Relativistic Astrophysics and Cosmology,MPE Report261,W.Voges et al.(eds) Brown B.A.,Bregman 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Exploring the complex X-ray spectrum of NGC 4051
a r X i v :a s t r o -p h /0310257v 2 16 J a n 2004Mon.Not.R.Astron.Soc.000,1–??(2003)Printed 2February 2008(MN L A T E X style file v1.4)Exploring the complex X-ray spectrum of NGC 4051.K.A.Pounds 1,J.N.Reeves 2,A.R.King 1and K.L.Page,11Department of Physics and Astronomy,University of Leicester,Leicester,LE17RH,UK2Laboratory for High Energy Astrophysics,NASA Goddard Space Flight Center,Greenbelt,MD 20771,USAAccepted ;SubmittedABSTRACTArchival XMM-Newton data on the nearby Seyfert galaxy NGC 4051,taken in rela-tively high and low flux states,offer a unique opportunity to explore the complexity of its X-ray spectrum.We find the hard X-ray band to be significantly affected by reflec-tion from cold matter,which can also explain a non-varying,narrow Fe K fluorescent line.We interpret major differences between the high and low flux hard X-ray spectra in terms of the varying ionisation (opacity)of a substantial column of outflowing gas.An emission line spectrum in the low flux state indicates an extended region of pho-toionised gas.A high velocity,highly ionised outflow seen in the high state spectrum can replenish the gas in the extended emission region over ∼103years,while having sufficient kinetic energy to contribute significantly to the hard X-ray continuum.Key words:galaxies:active –galaxies:Seyfert:general –galaxies:individual:NGC 4051–X-ray:galaxies1INTRODUCTIONThe additional sensitivity of XMM-Newton and Chandra has emphasised the complexity in the X-ray spectra of AGN.While there is broad agreement that the X-ray emission is driven by accretion onto a supermassive black hole,the detailed emission mechanism(s)remain unclear.Significant complexity -and diagnostic potential -is introduced by re-processing of the primary X-rays in surrounding matter.Scattering and fluorescence from dense matter in the pu-tative accretion disc has been recognised as a major fac-tor in modifying the observed X-ray emission of bright Seyfert galaxies since its discovery 13years ago (Nandra et al.1989,Pounds et al.1990).Additional modification of the observed X-ray spectra arises by absorption in passage through ionised matter in the line of sight to the continuum X-ray source.The high resolution X-ray spectra obtained with XMM-Newton and Chandra have shown the consider-able complexity of this ‘warm absorber’(eg Sako et al.2001,Kaspi et al.2002),including recent evidence for high veloc-ity outflows (eg Chartas et al.2002,Pounds et al.2003a,b;Reeves et al.2003)which constitute a significant component in the mass and energy budgets of those AGN.In this paper we report on the spectral analysis of two XMM-Newton ob-servations of the bright,nearby Seyfert 1galaxy NGC 4051taken from the XMM-Newton data archive.We find further support for the suggestion made in an early survey of XMM-Newton Seyfert spectra (Pounds and Reeves 2002),that the full effects of ionised absorption in AGN have often been underestimated.NGC 4051is a low redshift (z =0.0023)narrow lineSeyfert 1galaxy,which has been studied over much of the history of X-ray astronomy.Its X-ray emission often varies rapidly and with a large amplitude (Lawrence et al.1985,1987),occasionally lapsing into extended periods of ex-treme low activity (Lamer et al.2003).When bright,the broad band X-ray spectrum of NGC 4051appears typical of a Seyfert 1galaxy,with a 2–10keV continuum being well represented by a power law of photon index Γ∼1.8–2,with a hardening of the spectrum above ∼7keV being attributable to ‘reflection’from ‘cold’,dense matter,which might also be the origin of a relatively weak Fe K emission line (Nandra and Pounds 1994).However,NGC 4051also exhibits strong spectral variability,apparently correlated with source flux.The nature of this spectral variability has remained contro-versial since the GINGA data were alternatively interpreted as a change in power law slope (Matsuoka et al.1990)and by varying partial covering of the continuum source by op-tically thick matter (Kunieda et al.1992).Later ROSAT observations provided good evidence for a flux-linked variable ionised absorber,and for a ‘soft excess’below ∼1keV (Pounds et al.1994,McHardy et al.1995,Komossa and Fink 1997).Extended ASCA observations led Guainazzi et al.(1996)to report a strong and broad Fe K emission line (implying reflection from the inner accretion disc),and a positive correlation of the hard power law slope with X-ray flux.A 3-year monitoring campaign of NGC 4051with RXTE ,including a 150-day extended low interval in 1998,produced clear evidence for the cold reflection com-ponent (hard continuum and narrow 6.4keV Fe K line)re-c2003RAS2K.A.Pounds et al.maining constant,while againfinding the residual power law slope to steepen at higher X-rayfluxes(Lamer et al.2003). More surprisingly,a relativistic broad Fe K line component was found to be always present,even during the period whenthe Seyfert nucleus was‘switched off’(Guainazzi et al.1998, Lamer et al.2003).One other important contribution to the extensive X-ray literature on NGC4051came from an early Chandra observation which resolved two X-ray absorption line systems,with outflowing velocities of∼2300and∼600 km s−1,superimposed on a continuum soft excess with sig-nificant curvature(Collinge et al.2001).Of particular inter-est in the context of the present analysis,the higher velocity outflow is seen in lines of the highest ionisation potential. The Chandra data also show an unresolved Fe K emission line at∼6.41keV(FWHM≤2800km s−1).In summary,no clear picture emerges from a review of the extensive data on the X-ray spectrum of NGC4051, with the spectral variability being(mainly)due to a strong power law slope-flux correlation,or to variable absorption in(a substantial column of)ionised matter.Support for the former view has recently come from a careful study of the soft-to-hardflux ratios in extended RXTE data(Taylor et al.2003),while the potential importance of absorption is underlined by previous spectralfits to NGC4051requiring column densities of order∼1023cm−2(eg Pounds et al.1994, McHardy et al.1995).Given these uncertainties we decided to extract XMM-Newton archival data on NGC4051in order to explore its spectral complexities.After submission of the present paper, an independent analysis of the2002November EPIC pn data by Uttley et al.(2003)was published on astro-ph,reaching different conclusions to those wefind.We comment briefly on these alternative descriptions of the spectral variability of NGC4051in Section9.4.2OBSER V ATION AND DATA REDUCTION NGC4051was observed by XMM-Newton on2001May 16/17(orbit263)for∼117ksec,and again on2002Novem-ber22(orbit541)for∼52ksec.The latter observation was timed to coincide with an extended period of low X-ray emis-sion from NGC4051.These data are now public and have been obtained from the XMM-Newton data archive.X-ray data are available in both observations from the EPIC pn (Str¨u der et al.2001)and MOS2(Turner et al.2001)cameras, and the Reflection Grating Spectrometer/RGS(den Herder et al.2001).The MOS1camera was also in spectral mode in the2002observation.Both EPIC cameras were used in small window mode in thefirst observation,together with the mediumfilter,successfully ensuring negligible pile-up. The large window mode,with mediumfilter,was used in the second,lowflux state observation.The X-ray data were first screened with the latest XMM SAS v5.4software and events corresponding to patterns0-4(single and double pixel events)were selected for the pn data and patterns0-12for MOS1and MOS2.A low energy cut of300eV was applied to all X-ray data and known hot or bad pixels were removed. We extracted EPIC source counts within a circular region of45′′radius defined around the centroid position of NGC 4051,with the background being taken from a similar re-gion,offset from but close to the source.The netexposures Figure 1.Background-subtracted EPIC pn data for the2001 May(black)and2002November(red)observations of NGC4051 available for spectralfitting from the2001observation were 81.7ksec(pn),103.6ksec(MOS2),114.3ksec(RGS1)and 110.9ksec(RGS2).For the2002observation thefinal spec-tral data were of46.6ksec(pn),101.9ksec(MOS1and2), 51.6ksec(RGS1)and51.6ksec(RGS2).Data were then binned to a minimum of20counts per bin,to facilitate use of theχ2minimalisation technique in spectralfitting. Spectralfitting was based on the Xspec package(Arnaud 1996).All spectralfits include absorption due to the NGC 4051line-of-sight Galactic column of N H=1.32×1020cm−2 (Elvis et al.1989).Errors are quoted at the90%confidence level(∆χ2=2.7for one interesting parameter).We analysed the broad-band X-ray spectrum of NGC 4051integrated over the separate XMM-Newton observa-tions,noting the meanflux levels were markedly different, and perhaps representative of the‘high state’and‘low state’X-ray spectra of this Seyfert galaxy.[In fact the2001May X-rayflux is close to the historical mean for NGC4051, but we will continue to refer to it as the‘high state’for convenience].To obtain afirst impression of the spectral change we compare infigure1the background-subtracted spectra from the EPIC pn camera for orbits263and541. The same comparison for the EPIC MOS2data(not shown) is essentially identical.From∼0.3–3keV the spectral shape is broadly unchanged,with the2001flux level being a fac-tor∼5higher.From∼3keV up to the very obvious emission line at∼6.4keV theflux ratio decreases,indicating aflatter continuum slope in the low state spectrum over this energy band.On this simple comparison the∼6.4keV emission line appears essentially unchanged in energy,width and photon flux.We will defer a more detailed comparison of the‘high’and‘low’state data until Section5,afterfirst modelling the individual EPIC spectra.3HIGH STATE EPIC SPECTRUM3.1Power law continuumWe began our analysis of the EPIC data for2001May in the conventional way byfitting a power law over the hard X-ray (3–10keV)band,thereby excluding the more obvious effectsc 2003RAS,MNRAS000,1–??X-ray spectrum of NGC40513 Figure2.Ratio of data to power lawfits over the3–10keV bandfor the pn(black)and MOS(red)spectra in the high state2001May observation of NGC4051.of soft X-ray emission and/or low energy absorption.Thisfityielded a photon index ofΓ∼1.85(pn)andΓ∼1.78(MOS),but thefit was poor with significant residuals.In particularthe presence of a narrow emission line near6.4keV,and in-creasing positive residuals above9keV(figure2),suggestedthe addition of a cold reflection component to refine the con-tinuumfit,which we then modelled with PEXRAV in Xspec(Magdziarz and Zdziarski1995).Since the reflection compo-nent was not well constrained by the continuumfit,we leftfree only the reflection factor R(=Ω/2π,whereΩis thesolid angle subtended at the source),fixing the power lawcut-offat200keV and disc inclination at20◦,with all abun-dances solar.The outcome was an improvedfit,with∆χ2of40for R=0.8±0.2.The power law indexΓincreased by0.1for both pn and MOSfits.In all subsequentfits we thenset R=0.8(compatible with the strength of the6.4keVemission line).Based on this broad bandfit we obtained a2-10keVflux for the2001May observation of NGC4051of2.4×10−11erg s−1cm−2corresponding to a2-10keVluminosity of2.7×1041erg s−1(H0=75km s−1Mpc−1).3.2Fe K emission and absorptionThe power law plus reflection continuumfit at3–10keVleaves several residual features in both pn and MOS data,the significance of which are indicated by the combinedχ2of2068for1740degrees of freedom(dof).Visual examinationoffigure2shows,in particular,a narrow emission line near6.4keV and evidence of absorption near∼7keV and between∼8–9keV.To quantify these features we then added further spec-tral components to the model,beginning with a gaussianemission line with energy,width and equivalent width asfree parameters.This addition improved the3–10keVfit,toχ2/dof of1860/1735,with a line energy(in the AGN restframe)of6.38±0.01keV(pn)and6.42±0.03keV(MOS),rms width≤60eV and lineflux of1.6±0.4×10−5photons−1cm−2(pn)and1.4±0.6×10−5photon s−1cm−2(MOS),corresponding to an equivalent width(EW)of60±15eV.Next,wefitted the most obvious absorption feature near7keV with a gaussian shaped absorption line,again withenergy,width and equivalent width free.The best-fit ob-served line energy was7.15±0.05keV(pn)and7.05±0.05keV(MOS)in the AGN rest-frame,with an rms width of150±50eV,and an EW of100±20eV.The addition of thisgaussian absorption line gave a further highly significantimprovement to the overallfit,withχ2/dof=1802/1730.Fitting the less compelling absorption feature at∼8–9keVwith a second absorption line was not statistically signifi-cant.However,an absorption edge did improve thefit toχ2/dof=1767/1728,for an edge energy of8.0±0.1keV andoptical depth0.15±0.05.In summary,the3-10keV EPIC data from the highstate2001May observation of NGC4051is dominated by apower law continuum,with a photon index(after inclusionof cold reflection plus an emission and absorption line)of1.90±0.02(pn)and1.84±0.02(MOS).The narrow emissionline at∼6.4keV is compatible withfluorescence from thesame cold reflecting matter,while-if identified with reso-nance absorption of FeXXVI or FeXXV-the∼7.1keV lineimplies a substantial outflow of highly ionised gas.Wefindno requirement for the previously reported strong,broad FeK emission line,the formal upper limit for a line of initialenergy6.4keV being70eV.3.3Soft ExcessExtending the above3–10keV continuum spectralfit downto0.3keV,for both pn and MOS data,shows very clearly(figure3)the strong soft excess indicated in earlier observa-tions of NGC4051.To quantify the soft excess we againfitted the com-bined pn and MOS data,obtaining a reasonable overallfit with the addition of blackbody continua of kT∼120and270eV,together with absorption edges at∼0.725keV(τ∼0.24)and∼0.88keV(τ∼0.09).Based on this broad bandfit we deduced soft X-rayflux levels for the2001May ob-servation of NGC4051of2.9×10−11erg s−1cm−2(0.3–1keV),with∼61percent in the blackbody components,and1.1×10−11erg s−1cm−2(1–2keV).Combining these re-sults with the higher energyfit yields an overall0.3–10keVluminosity of NGC4051in the‘high’state of7×1041ergs−1(H0=75km s−1Mpc−1).4LOW STATE EPIC SPECTRUMThe above procedure was then repeated in an assessment ofthe2002November EPIC data,when the X-rayflux fromNGC4051was a factor∼4.5lower(figure1).Fitting the hard X-ray continuum was now more un-certain since the spectrum was more highly curved in thelowflux state(comparefigs4and2),making an underlyingpower law component difficult to identify.To constrain thefitting parameters we therefore made two important initialassumptions.Thefirst,supported by the minimal changeapparent in the narrow Fe K line,was to carry forward thecold reflection(normalisation and R)parameters from the‘high state’spectralfit(in fact,as noted above,appropri-ately at aflux level close to the historical average for NGC4051).The second assumption was that the power law con-tinuum changed only in normalisation,but not in slope(as c 2003RAS,MNRAS000,1–??4K.A.Pounds etal.Figure3.Extrapolation to0.3keV of the3–10keV spectralfit(detailed in section3.2)showing the strong soft excess in both pn(black)and MOS(red)spectra during the2001May observationof NGC4051.found in the extended XMM-Newton observation of MCG-6-30-15,Fabian and Vaughan2003).This is in contrast to theconclusions of Lamer et al.(2003)but-as we see later-isconsistent with the difference spectrum(figure8),whichfitsquite well at3–10keV to a power law slope ofΓ∼2,whilealso showing no significant residual reflection features.With these initial assumptions,the3–10keVfit to thelow state spectrum yielded the data:model ratio shown infig-ure4.A visual comparison withfigure2shows a very similarnarrow emission line at∼6.4keV,but with strong curvatureto the underlying continuum,and significant differences inthe absorption features above7keV.These strong residualsresulted in a very poorfit at3–10keV,withχ2of1610/990.We note the spectral curvature in the3–6keV band is rem-iniscent of an extreme relativistic Fe K emission line;how-ever,since our high state spectrum showed no evidence forsuch a feature,and it might in any case be unexpected whenthe hard X-ray illumination of the innermost accretion discis presumably weak,we considered instead a model in whicha fraction of the power law continuum is obscured by anionised absorber.We initially modelled this possibility withABSORI in Xspec,finding both the3–6keV spectral cur-vature and the absorption edge at∼7.6keV were wellfittedwith∼60percent of the power law covered by ionised matterof ionisation parameterξ(=L/nr2)∼25and column densityN H∼1.2×1023cm−2.The main residual feature was then the narrow Fe Kemission line.4.1The narrow Fe K emission lineA gaussian linefit to the emission line at∼6.4keV in thelow state EPIC data was again unresolved,with a meanenergy(in the AGN rest frame)of6.41±0.01keV(pn)and6.39±0.02keV(MOS),and linefluxes of1.9±0.3×10−5pho-ton s−1cm−2(pn)and2.0±0.4×10−5photon s−1cm−2(MOS),corresponding to an EW against the unabsorbedpower law component of500±75eV.The important pointis that,within the measurement errors,the measuredfluxesof the∼6.4keV line are the same for the twoobservations.Figure4.Ratio of data to power law plus continuum reflectionmodelfit over the3–10keV band for the pn(black)and MOS(red)spectra in the low state2002November observation of NGC4051.Figure5.Partial covering model spectrumfitted over the3–10keV band for the2002November observation of NGC4051.Alsoshown are the separate components in thefit:the unabsorbedpower law(green),absorbed power law(red)and Gaussian emis-sion line(blue).See Section4.1for details.For clarity only thepn data are shown.This lends support to our initial assumption that both EPICspectra include a‘constant’reflection component,illumi-nated by the long-term average hard X-ray emission fromNGC4051.With the addition of this narrow emission linethe overall3–10keVfit obtained with the partial coveringmodel was then good(χ2/dof=1037/1037).Figure5illus-trates the unfolded spectrum and spectral components ofthisfit.4.2Soft ExcessExtrapolation of the above partial covering3–10keV spec-tralfit down to0.3keV shows a substantial soft X-ray excessremains(figure6),with a similar relative strength to thepower law component seen in the high state data.We notethat the‘soft excess’,ie relative to the power law component,c 2003RAS,MNRAS000,1–??X-ray spectrum of NGC40515 Figure6.Partial covering modelfits over the3–10keV bandextended to0.3keV,for the pn(black)and MOS(red)data fromthe low state2002November observation of NGC4051.would have been extremely strong(data:model ratio∼8)had we taken the simple power lawfit(Γ∼1.4)to the lowstate3–10keV data.Extending the partial covering model to0.3keV,with the addition-as in the high state-of a black-body component of kT∼125eV(the hotter component wasnot required),gave an initially poorfit(χ2of2348for1265dof for the pn data),with a broad deficit in observedfluxat∼0.7-0.8keV being a major contributor(figure6).Theaddition of a gaussian absorption line to the partial coveringmodel gave a large improvement to the broad-bandfit(toχ2of1498for1262dof),for a line centred at0.756±0.003keV,with rms width50±15eV and EW∼40eV.We show thiscomplex spectralfit infigure7,and comment that the modeldependency of unfolded spectra is relatively unimportant inillustrating such strong,broad band spectral features.Sig-nificantly,the broad-band spectralfit remains substantiallyinferior to the similarfit to the high state data.Examina-tion of the spectral residuals shows this is due to additionalfine structure in the soft band of the low state spectrum,structure that is also evident infigures6and7.We examinethe RGS data in Section6to explore the nature(absorptionor emission)of this structure.The deduced soft X-rayflux levels for the2002Novem-ber observation of NGC4051were6.3×10−12erg s−1cm−2(0.3–1keV),with∼53percent in the blackbody component,and1.8×10−12erg s−1cm−2(1–2keV).Combining these re-sults with a2-10keVflux of5.8×10−12erg s−1cm−2yieldedan overall0.3–10keV luminosity of NGC4051in the‘low’state of1.5×1041erg s−1(H0=75km s−1Mpc−1).5COMPARISON OF THE HIGH AND LOWSTATE EPIC DATAThe above spectralfitting included two important assump-tions,that the cold reflection was unchanged between thehigh and lowflux states,and the variable power law com-ponent was of constant spectral index.We now compare theEPIC data for the two observations to further explore thenature of the spectral change.Figure8illustrates the dif-ference spectrum obtained by subtracting thebackground-Figure7.Extrapolation to0.3keV of the3–10keV partial cov-eringfit offig5showing the strong soft excess modelled by ablackbody component(blue),and a broad absorption trough at∼0.76keV.For clarity only the pn data are shown.subtracted low state data from the equivalent high state data(corrected for exposure).To improve the statistical signifi-cance of the higher energy points the data were re-groupedfor a minimum of200counts.The resulting difference spec-trum is compared infigure8with a power lawfitted at3–10keV.Several points are of interest.First,the power law indexof the difference spectrum,Γ∼2.04(pn)andΓ∼1.97(M2),is consistent with the assumed‘constant’value in the indi-vidual spectralfits.Second,the narrow Fe K emission lineand high energy data upturn are not seen,supporting ourinitial assumption of a‘constant’cold reflection component.The narrow feature observed at∼7keV corresponds to theabsorption line seen(only)in the high state spectrum,whilewe shall see in Section6that the deficit near0.55keV inthe MOS data(which has substantially better energy reso-lution there than the pn)is probably explained by a strongand‘constantflux’emission line of OVII.Finally,the smallpeak near8keV can be attributed to the absorption edgeshifting to lower energy as the photoionised gas recombinesin the reduced continuum irradiation.While the arithmetic difference of two spectra providesa sensitive check for the variability of additive spectral com-ponents,a test of the variability of multiplicative compo-nents is provided by the ratio of the respective data sets.Figure9reproduces the ratio of the high and low state data(pn only)after re-grouping to a minimum of500counts perbin.From∼0.3–3keV theflux ratio averages∼5,as seen infigure1,falling to higher energies as the mean slope of thelow state spectrum hardens.The large positive feature at∼0.7–0.8keV is of particular interest,indicating a variablemultiplicative component,almost certainly corresponding toenhanced absorption in the low state spectrum.In fact thatfeature can be clearly seen in the low state EPIC data infigures6and7.We suggest the broad excess at∼1–2keVcan be similarly explained by greater absorption affectingthe low state spectrum,lending support to our overall inter-pretation of the spectral change.Finally,we note that thenarrow dip in the ratio plot at∼6.4keV is consistent withthe Fe K emission line having unchangedflux,but corre-spondingly higher EW in the low state spectrum.c 2003RAS,MNRAS000,1–??6K.A.Pounds etal.Figure8.High minus low state difference spectral data(pn-black,M2-red)compared with a simple power law,as describedin Section5.Figure9.Ratio of high state to low state spectral data(pn only),as described in Section5.6SPECTRAL LINES IN THE RGS DATABoth EPIC spectra show a strong soft excess,with the lowstate(2002)spectrum also having more evidence offinestructure.To study the soft X-ray spectra in more detailwe then examined the simultaneous XMM-Newton gratingdata for both observations of NGC4051.Figures10and11reproduce thefluxed spectra,binned at35m˚A,to showboth broad and narrow features.The continuumflux level ishigher in the2001data(consistent with the levels seen in theEPIC data),with a more pronounced curvature longwardsof∼15˚A.Numerous sharp data drops hint at the presence ofmany narrow absorption lines.In contrast,the2002Novem-ber RGS spectrum exhibits a lower andflatter continuumflux,and a predominance of narrow emission lines.We began an analysis of each observation by simultane-ouslyfitting the RGS-1and RGS-2data with a power lawand black body continuum(from the corresponding EPIC0.3–10keVfits)and examining the data:model residuals byeye.For the2001May observation the strongest featureswere indeed narrow absorption lines,most beingreadilyFigure10.Fluxed RGS spectrum from the XMM-Newton ob-servation of NGC4051in2001May.Figure11.Fluxed RGS spectrum from the XMM-Newton ob-servation of NGC4051in2002November.identified with resonance absorption in He-and H-like ionsof C,N,O and Ne.In contrast,the combined RGS data forthe low state data from2002November showed a mainlyemission line spectrum,more characteristic of a Seyfert2galaxy(eg Kinkhabwala et al.2002).Significantly,the NVI,OVII and NeIX forbidden lines are seen in both high andlow state RGS spectra at similarflux levels.Taking note ofthat fact we then analysed the low state(2002)datafirst,and subsequently modelled the RGS high-minus-low differ-ence spectrum,to get a truer measure of the absorption linestrengths in the high state(2001)spectrum.6.1An emission line spectrum in the low statedataTo quantify the emission lines in the2002spectrum weadded gaussian lines to the power law plus blackbody contin-uumfit in Xspec,with wavelength andflux as free parame-ters.In each case the line width was unresolved,indicating aFWHM≤300km s−1.Details of the8strongest lines therebyidentified are listed in Table1.The statistical quality of thec 2003RAS,MNRAS000,1–??X-ray spectrum of NGC40517fit was greatly improved by the addition of the listed lines,with a reduction inχ2of251for16fewer dof.When ad-justed for the known redshift of NGC4051all the identified lines are consistent with the laboratory wavelengths indi-cating that the emitting gas has a mean outflow(or inflow) velocity of≤200km s−1.Figure12illustrates the OVII triplet,showing the dom-inant forbidden line and strong intercombination line emis-sion,but no residual resonance line emission(at21.6˚A).Theline ratios,consistent with those found in the earlier Chandra observation(Collinge et al.2001),give a clear signature of a photoionised plasma,with an electron density≤1010cm−3(Porquet and Dubau2000).A similarly dominant forbidden line in the NVI triplet yields a density limit a factor∼10 lower.We note the absence of the OVII resonance emission line may be due to infilling by a residual absorption line ofsimilar strength.After removal of the emission lines listed in Table1,sev-eral additional emission features(seefigure11)remained. Although narrow and barely resolved,the wavelength of these features allows them to be unambiguously identifiedwith the radiative recombination continua(RRC)from the same He-and H-like ions of C,N,O and(probably)Ne. Table2lists the properties of these RRC as determined byfitting in Xspec with the REDGE model.While the RRC of CV,CVI,NVI and OVII are well determined,wefixed the other threshold energies at their laboratory values to quan-tify the measured equivalent widths.What is clear is that the RRC are very narrow,a combinedfit yielding a mean temperature for the emitting gas of kT∼3eV(T∼4×104K).We note this low temperature lies in a region of thermal stability for such a photoionised gas(Krolik et al.1981). Furthermore,the low temperature indicates collisional ion-isation and excitation will be negligible,and radiative re-combination should be the dominant emission process.Additional constraints on the emitting gas in NGC4051can be derived by noting that the2002November XMM-Newton observation took place some20days after the source entered an extended lowflux state.Furthermore,the emis-sion line strength of the OVII forbidden line is essentially the same as when NGC4051was much brighter in2001 May.This implies that the emission spectrum arises fromionised matter which is widely dispersed and/or of such low density that the recombination time is>∼2×106s.At a gas temperature of∼4×104K,the recombination time for OVIIis of order150(n9)−1s,where n9is the number density of the ionised matter in units of109cm−3(Shull and Van Steenberg 1982).The persistent low state emission would therefore in-dicate a plasma density≤105cm−3.Assuming a solar abundance of oxygen,with30per-cent in OVII,50percent of recombinations from OVIII di-rect to the ground state,and a recombination rate at kT ∼3eV of10−11cm3s−1(Verner and Ferland1996),we deduce an emission measure for the forbidden lineflux oforder2×1063cm−3.That corresponds to a radial extent of >∼3×1017cm for a uniform spherical distribution of pho-toionised gas at the above density of≤105cm−3.Coinci-dentally,the alternative explanation for a constant emission lineflux,via an extended light travel time,also requires an emitting region scale size of>∼1017cm.We note,furthermore, that these values of particle density and radial distance from the ionising continuum source are consistent with theioni-Figure12.Emission lines dominate the2002November RGS data.The OVII triplet is illustrated with only the forbidden and intercombination lines clearly visible.The gaussian linefits in-clude only the RGS resolution showing the emission lines are in-trinsically narrow.See Section6.1for details.sation parameter derived from our XSTARfit to the RGS absorption spectrum(Section7).The scale of the soft X-ray emitting gas is apparently much greater than the BLR, for which Shemmer et al.2003find a value of3.0±1.5light days(∼3−10×1015cm).In fact it has overall properties,of density,temperature and velocity consistent with the NLR in NGC4051.The above emission lines and RRC provide an accept-ablefit to the RGS data for the2002November observation of NGC4051.However a coarse binning of the data:model residuals(figure13)shows a broad deficit offlux remaining at∼15−17˚A.It seems likely that this feature is the same as that seen in the broad bandfits to the EPIC data for 2002November(Section4)and tentatively identified with an unresolved transition array(UTA)from Fe M-shell ions (Behar et al.2001).Whenfitted with a gaussian absorp-tion line wefind an rms width ofσ=∼30eV and EW of 25eV against the low state continuum,consistent with the absorption trough required in the partial coveringfit to the low state EPIC data(section4.2).6.2Absorption lines in the high state differencespectrum.The observed wavelengths of the main emission lines in the 2002spectrum and their equivalent absorption lines in the 2001spectrum are the same within the resolution of our gaussian linefitting.(At higher resolution the absorption lines appear to have a mean outflow velocity of∼500km s−1,while the emission lines are close to the systemic veloc-ity of NGC4051.)Furthermore,from our analysis in Section 6.1it seems clear that the emission line spectrum represents an underlying component that responds to some long-term averageflux level of the ionising continuum of NGC4051. We thereforefirst subtracted the2002RGS spectrum from the2001spectrum with the aim of obtaining a truer mea-sure of the absorption line strengths in the high state data. Quantifying the main absorption lines by adding gaussianc 2003RAS,MNRAS000,1–??。
Handbook_of_X-Ray_Spectrometry_CH01
1X-ray PhysicsAndrzej A.MarkowiczVienna,AustriaI.INTRODUCTIONIn this introductory chapter,the basic concepts and processes of x-ray physics that relate to x-ray spectrometry are presented.Special emphasis is on the emission of the continuum and characteristic x-rays as well as on the interactions of photons with matter.In the latter,only major processes of the interactions are covered in detail,and the cross sections for different types of interactions and the fundamental parameters for other processes involved in the emission of the characteristic x-rays are given by the analytical expressions and=or in a tabulated form.Basic equations for the intensity of the characteristic x-rays for the different modes of x-ray spectrometry are also presented(without derivation). Detailed expressions relating the emitted intensity of the characteristic x-rays to the concentration of the element in the specimen are discussed in the subsequent chapters of this handbook dedicated to specific modes of x-ray spectrometry.II.HISTORYX-rays were discovered in1895by Wilhelm Conrad Ro ntgen at the University of Wu rzburg,Bavaria.He noticed that some crystals of barium platinocyanide,near a dis-charge tube completely enclosed in black paper,became luminescent when the discharge occurred.By examining the shadows cast by the rays.Ro ntgen traced the origin of the rays to the walls of the discharge tube.In1896,Campbell-Swinton introduced a definite target (platinum)for the cathode rays to hit;this target was called the anticathode.For his work x-rays,Ro ntgen received thefirst Nobel Prize in physics,in1901.It was thefirst of six to be awarded in thefield of x-rays by1927.The obvious similarities with light led to the crucial tests of established wave optics: polarization,diffraction,reflection,and refraction.With limited experimental facilities, Ro ntgen and his contemporaries couldfind no evidence of any of these;hence,the des-ignation‘‘x’’(unknown)of the rays,generated by the stoppage at anode targets of the cathode rays,identified by Thomson in1897as electrons.The nature of x-rays was the subject of much controversy.In1906,Barkla found evidence in scattering experiments that x-rays could be polarized and must therefore by waves,but W.H.Bragg’s studies of the produced ionization indicated that they werecorpuscular.The essential wave nature of x-rays was established in1912by Laue, Friedrich,and Knipping,who showed that x-rays could be diffracted by a crystal(copper sulfate pentahydrate)that acted as a three-dimensional diffraction grating.W.H.Bragg and W.L.Bragg(father and son)found the law for the selective reflection of x-rays.In 1908,Barkla and Sadler deduced,by scattering experiments,that x-rays contained com-ponents characteristic of the material of the target;they called these components K and L radiations.That these radiations had sharply defined wavelengths was shown by the diffraction experiments of W.H.Bragg in1913.These experiments demonstrated clearly the existence of a line spectrum superimposed upon a continuous(‘‘White’’)spectrum.In 1913,Moseley showed that the wavelengths of the lines were characteristic of the element of the which the target was made and,further,showed that they had the same sequence as the atomic numbers,thus enabling atomic numbers to be determined unambiguously for thefirst time.The characteristic K absorption wasfirst observed by de Broglie and in-terpreted by W.L.Bragg and Siegbahn.The effect on x-ray absorption spectra of the chemical state of the absorber was observed by Bergengren in1920.The influence of the chemical state of the emitter on x-ray emission spectra was observed by Lindh and Lundquist in1924.The theory of x-ray spectra was worked out by Sommerfeld and others.In1919,Stenstro m found the deviations from Bragg’s law and interpreted them as the effect of refraction.The anomalous dispersion of x-ray was discovered by Larsson in 1929,and the extendedfine structure of x-ray absorption spectra was qualitatively in-terpreted by Kronig in1932.Soon after thefirst primary spectra excited by electron beams in an x-ray tube were observed,it was found that secondaryfluorescent x-rays were excited in any material ir-radiated with beams of primary x-rays and that the spectra of thesefluorescent x-rays were identical in wavelengths and relative intensities with those excited when the specimen was bombarded with electrons.Beginning in1932,Hevesy,Coster,and others investigated in detail the possibilities offluorescent x-ray spectroscopy as a means of qualitative and quantitative elemental analysis.III.GENERAL FEATURESX-rays,or Ro ntgen rays,are electromagnetic radiations having wavelengths roughly within the range from0.005to10nm.At the short-wavelength end,they overlap with g-rays,and at the long-wavelength end,they approach ultraviolet radiation.The properties of x-rays,some of which are discussed in detail in this chapter,are summarized as follows:InvisiblePropagated in straight lines with a velocity of36108m=s,as is lightUnaffected by electrical and magneticfieldsDifferentially absorbed while passing through matter of varying composition, density,or thicknessReflected,diffracted,refracted,and polarizedCapable of ionizing gasesCapable of affecting electrical properties of liquids and solidsCapable of blackening a photographic plateAble to liberate photoelectrons and recoil electronsCapable of producing biological reactions(e.g.,to damage or kill living cells and to produce genetic mutations)Emitted in a continuous spectrum whose short-wavelength limit is determined onlyby the voltage on the tubeEmitted also with a line spectrum characteristic of the chemical elementsFound to have absorption spectra characteristic of the chemical elementsIV.EMISSION OF CONTINUOUS RADIA TIONContinuous x-rays are produced when electrons,or other high-energy charged particles,such as protons or a -particles,lose energy in passing through the Coulomb field of a nucleus.In this interaction,the radiant energy (photons)lost by the electron is called bremsstrahlung (from the German bremsen ,to brake,and Strahlung ,radiation;this term sometimes designates the interaction itself).The emission of continuous x-rays finds a simple explanation in terms of classic electromagnetic theory,because,according to this theory,the acceleration of charged particles should be accompanied by the emission of radiation.In the case of high-energy electrons striking a target,they must be rapidly decelerated as they penetrate the material of the target,and such a high negative accel-eration should produce a pulse of radiation.The continuous x-ray spectrum generated by electrons in an x-ray tube is char-acterized by a short-wavelength limit l min ,corresponding to the maximum energy of the exciting electrons:l min ¼hceV 0ð1Þwhere h is Planck’s constant,c is the velocity of light,e is the electron charge,and V 0is the potential difference applied to the tube.This relation of the short-wavelength limit to the applied potential is called the Duane–Hunt law.The probability of radiative energy loss (bremsstrahlung)is roughly proportional to q 2Z 2T =M 20,where q is the particle charge in units of the electron charge e ,Z is the atomic number of the target material,T is the particle kinetic energy,and M 0is the rest mass of the particle.Because protons and heavier particles have large masses compared to the electron mass,they radiate relatively little;for example,the intensity of continuous x-rays generated by protons is about four orders of magnitude lower than that generated by electrons.The ratio of energy lost by bremsstrahlung to that lost by ionization can be approximated bym 0M 0 2ZT 1600m 0c ð2Þwhere m 0the rest mass of the electron.A.Spectral DistributionThe continuous x-ray spectrum generated by electrons in an x-ray tube (thick target)is characterized by the following features:1.Short-wavelength limit,l min [Eq.(1)];below this wavelength,no radiation isobserved.2.Wavelength of maximum intensity l max ,approximately 1.5times l min ;however,the relationship between l max and l min depends to some extent on voltage,voltage waveform,and atomic number.3.Total intensity nearly proportional to the square of the voltage and the firstpower of the atomic number of the target material.The most complete empirical work on the overall shape of the energy distribution curve for a thick target has been of Kulenkampff(1922,1933),who found the following formula for the energy distribution;I ðv Þdv ¼i aZ v 0Àv ðÞþbZ 2ÂÃdvð3Þwhere I ðn Þd n is the intensity of the continuous x-rays within a frequency range ðn ;n þdv Þ;i is the electron current striking the target,Z is the atomic number of the target material,n 0is the cutofffrequency ð¼c =l min Þabove which the intensity is zero,and a and b are constants independent of atomic number,voltage,and cutoffwavelength.The second term in Eq.(3)is usually small compared to the first and is often neglected.The total integrated intensity at all frequencies isI ¼i ða 0ZV 20þb 0Z 2V 0Þð4Þin which a 0¼a ðe 2=h 2Þ=2and b 0¼b ðe =h Þ.An approximate value for b 0=a 0is 16.3V;thus,I ¼a 0iZV 0ðV 0þ16:3Z Þð5ÞThe efficiency Effof conversion of electric power input to x-rays of all frequencies is given byEff ¼I V 0i ¼a 0Z ðV 0þ16:3Z Þð6Þwhere V 0is in volts.Experiments give a 0¼ð1:2Æ0:1ÞÂ10À9(Condon,1958).The most complete and successful efforts to apply quantum theory to explain all features of the continuous x-ray spectrum are those of Kramers (1923)and Wentzel (1924).By using the correspondence principle,Kramers found the following formulas for the energy distribution of the continuous x-rays generated in a thin target:I ðv Þdv ¼16p 2AZ 2e53ffiffi3p m 0V 0c 3dv ;v <v 0I ðv Þdv ¼0;v >v 0ð7Þwhere A is the atomic mass of the target material.When the decrease in velocity of the electrons in a thick target was taken into account by applying the Thomson–Whiddington law (Dyson,1973),Kramers found,for a thick target,I ðv Þdv ¼8p e 2h 3ffiffiffi3p lm 0c 3Z ðv 0Àv Þdv ð8Þwhere l is approximately 6.The efficiency of production of the x-rays calculated via Kramers’law is given byEff ¼9:2Â10À10ZV 0ð9Þwhich is in qualitative agreement with the experiments of Kulenkampff(Stephenson,1957);for example,Eff ¼15Â10À10ZV 0ð10ÞIt is worth mentioning that the real continuous x-ray distribution is described only ap-proximately by Kramers’equation.This is related,inter alia ,to the fact that the derivation ignores the self-absorption of x-rays and electron backscattering effects.Wentzel (1924)used a different type of correspondence principle than Kramers,and he explained the spatial distribution asymmetry of the continuous x-rays from thin targets.An accurate description of continuous x-rays is crucial in all x-ray spectrometry (XRS).The spectral intensity distributions from x-ray tubes are of great importance for applying fundamental mathematical matrix correction procedures in quantitative x-ray fluorescence (XRF)analysis.A simple equation for the accurate description of the actual continuum distributions from x-ray tubes was proposed by Tertian and Broll (1984).It is based on a modified Kramers’law and a refined x-ray absorption correction.Also,a strong need to model the spectral Bremsstrahlung background exists in electron-probe x-ray microanalysis (EPXMA).First,fitting a function through the background portion,on which the characteristic x-rays are superimposed in an EPXMA spectrum,is not easy;several experimental fitting routines and mathematical approaches,such as the Simplex method,have been proposed in this context.Second,for bulk multielement specimens,the theoretical prediction of the continuum Bremsstrahlung is not trivial;indeed,it has been known for several years that the commonly used Kramers’formula with Z directly sub-stituted by the average "Z ¼P i W i Z i (W i and Z i are the weight fraction and atomic number of the i th element,respectively)can lead to significant errors.In this context,some im-provements are offered by several modified versions of Kramers’formula developed for a multielement bulk specimen (Statham,1976;Lifshin,1976;Sherry and Vander Sande,1977;Smith and Reed,1981).Also,a new expression for the continuous x-rays emitted by thick composite specimens was proposed (Markowicz and Van Grieken,1984;Markowicz et al.,1986);it was derived by introducing the compositional dependence of the continuum x-rays already in the elementary equations.The new expression has been combined with known equations for the self-absorption of x-rays (Ware and Reed,1973)and electron back-scattering (Statham,1979)to obtain an accurate description of the detected continuum radiation.A third problem is connected with the description of the x-ray continuum gen-erated by electrons in specimens of thickness smaller than the continuum x-ray generation range.This problem arises in the analysis of both thin films and particles by EPXMA.A theoretical model for the shape of the continuous x-rays generated in multielement specimens of finite thickness was developed (Markowicz et al.,1985);both composition and thickness dependence have been considered.Further refinements of the theoretical approach are hampered by the lack of knowledge concerning the shape of the electron interaction volume,the distribution of the electron within the interaction volume,and the anisotropy of continuous radiation for different x-ray energies and for different film thickness.B.Spatial Distribution and PolarizationThe spatial distribution of the continuous x-rays emitted by thin targets has been in-vestigated by Kulenkampff(1928).The author made an extensive survey of the intensity at angles between 22 and 150 to the electron beam in terms of dependence on wavelength and voltage.The target was a 0.6-m m-thick Al foil.Figure 1shows the continuous x-ray intensity observed at different angles for voltages of 37.8,31.0,24.0,and 16.4kV filtered by 10,8,4,and 1.33mm of Al,respectively (Stephenson,1957).Curve (a)is repeated as a dotted line near each of the other curves.The angle of the maximum intensity varied from50 for 37.8kV to 65 for 16.4kV.Figure 2illustrates the intensity of the continuous x-rays observed in the Al foil for different thicknesses as a function of the angle for a voltage of 30kV (Stephenson,1957).The theoretical curve is from the theory of Scherzer (1932).The continuous x-ray intensity drops to zero at 180 ,and although it is not zero at 0 as the theory of Scherzer predicts,it can be seen from Figure 2that for a thinner foil,a lower intensity at 0 is obtained.Summarizing,it appears that the intensity of the con-tinuous x-rays emitted by thin foils has a maximum at about 55 relative to the incident electron beam and becomes zero at 180 .The continuous radiation from thick targets is characterized by a much smaller anisotropy than that from thin targets.This is because in thick targets the electrons are rarely stopped in one collision and usually their directions have considerable variation.The use of electromagnetic theory predicts a maximum energy at right angles to the in-cident electron beam at low voltages,with the maximum moving slightly away from perpendicularity toward the direction of the elctron beam as the voltage is increased.In general,an increase in the anisotropy of the continuous x-rays from thick targets is ob-served at the short-wavelength limit and for low-Z targets (Dyson,1973).Figure1Intensity of continuous x-rays as a function of direction for different voltages.(Curve (a)is repeated as dotted line.)(From Stephenson,1957.)Continuous x-ray beams are partially polarized only from extremely thin targets;the angular region of polarization is sharply peaked about the photon emission angle y ¼m 0c 2=E 0,where E 0is the energy of the primary electron beam.Electron scattering in the target broadens the peak and shifts the maximum to larger angles.Polarization is defined by (Kenney,1966)P ðy ;E 0;E n Þ¼d s ?ðy ;E 0;E n ÞÀd s kðy ;E 0;E n Þd s ?ðy ;E 0;E n Þþd s kðy ;E 0;E n Þð11Þwhere an electron of energy E 0radiates a photon of energy E n at angle y ;d s ?ðy ;E 0;E n Þand d s kðy ;E 0;E n Þare the cross sections for generation of the continuous radiation with the electric vector perpendicular (?)and parallel (k )to the plane defined by the incident electron and the radiated photon,respectively.Polarization is difficult to observe,and only thin,low-yield radiators give evidence for this effect.When the electron is relativistic before and after the radiation,the electrical vector is most probably in the ?direction.Practical thick-target Bremsstrahlung shows no polarization effects whatever (Dyson,1973;Stephenson,1957;Kenney,1966).V.EMISSION OF CHARACTERISTIC X-RA YSThe production of characteristic x-rays involves transitions of the orbital electrons of atoms in the target material between allowed orbits,or energy states,associated with ionization of the inner atomic shells.When an electron is ejected from the K shell by electron bombardment or by the absorption of a photon,the atom becomes ionized and the ion is left in a high-energy state.The excess energy the ion has over the normal state of the atom is equal to the energy (the binding energy)required to remove the K electron to a state of rest outside the atom.If this electron vacancy is filled by an electron coming from an L level,the transition is accompanied by the emission of an x-ray line known as the K a line.This process leaves a vacancy in the L shell.On the other hand,if the atom contains sufficient electrons,the K shell vacancy might be filled by an electron coming from an M level that is accompanied by the emission of the K b line.The L or M state ions that remain may also give rise to emission if the electron vacancies are filled by electrons falling from furtherorbits.Figure 2Intensity of continuous x-rays as a function of direction for different thicknesses of the A1target together with theoretical prediction.(From Stephenson,1957.)A.Inner Atomic Shell IonizationAs already mentioned,the emission of characteristic x-ray is preceded by ionization of inner atomic shells,which can be accomplished either by charged particles(e.g.,electrons, protons,and a-particles)or by photons of sufficient energy.The cross section for ion-ization of an inner atomic shell of element i by electrons is given by(Bethe,1930;Green and Cosslett,1961;Wernisch,1985)Q i¼p e4n s b s ln UUEc;ið12Þwhere U¼E=E c;i is the overvoltage,defined as the ratio of the instantaneous energy of the electron at each point of the trajectory to that required to ionize an atom of element i,E c;i is the critical excitation energy,and n s and b s are constants for a particular shell: s¼K:n s¼2;b s¼0:35s¼L:n s¼8;b s¼0:25The cross section for ionization Q i is a strong function of the overvoltage,which shows a maximum at Uffi3–4(Heinrich,1981;Goldstein et al.,1981).The probability(or cross section)of ionization of an inner atomic shell by a charged particle is given by(Merzbacher and Lewis,1958)s s¼8p r2q2f sZ Z sð13Þwhere r0is the classic radius of the electron equal to2.818610À15m,q is the particle charge,Z is the atomic number of the target material,f s is a factor depending on the wave functions of the electrons for a particular shell,and Z s is a function of the energy of the incident particles.In the case of electromagnetic radiation(x or g),the ionization of an inner atomic shell is a result of the photoelectric effect.This effect involves the disappearance of a ra-diation photon and the photoelectric ejection of one electron from the absorbing atom, leaving the atom in an excited level.The kinetic energy of the ejected photoelectron is given by the difference between the photon energy h n and the atomic binding energy of the electron E c(critical excitation energy).Critical absorption wavelengths(Clark,1963)re-lated to the critical absorption energies(Burr,1974)via the equation l(nm)¼1.24=E(ke V) are presented in Appendix I.The wavelenghts of K,L,M,and N absorption edges can also be calculated by using simple empirical equations(Norrish and Tao,1993).For energies far from the absorption edge and in the nonrelativistic range,the cross section t K for the ejection of an electron from the K shell is given by(Heitler,1954)t K¼32ffiffiffi2p3p r20Z5ð137Þm0c2hv7=2ð14ÞEquation(14)is not fully adequate in the neighborhood of an absorption edge;in this case,Eq.(14)should be multiplied by a correction factor f(X)(Stobbe,1930):fðXÞ¼2p D hv1=2eÀ4X arccot X1ÀeÀ2p Xð15ÞwhereX¼DhvÀD1=2ð15aÞwithDffi12ðZÀ0:3Þ2m0c2ð137Þ2ð15bÞWhen the energy of the incident photon is of the order m0c2or greater,relativistic cross sections for the photoelectric effect must be used(Sauter,1931).B.Spectral Series in X-raysThe energy of an emission line can be calculated as the difference between two terms,each term corresponding to a definite state of the atom.If E1and E2are the term values re-presenting the energies of the corresponding levels,the frequency of an x-ray line is given by the relationv¼E1ÀE2hð16ÞUsing the common notations,one can represent the energies of the levels E by means of the atomic number and the quantum numbers n,l,s,and j(Sandstro m,1957):E Rh ¼ðZÀS n;lÞ2n2þa2ðZÀd n;l;jÞ2n31lþ12À34n!Àa2ðZÀd n;l;jÞ4n3jðjþ1ÞÀlðlþ1ÞÀsðsþ1Þ2lðlþ12Þðlþ1Þð17Þwhere S n;l and d n;l;j are screening constants that must be introduced to correct for the effect of the electrons on thefield in the atom,R is the universal Rydberg constant valid for all elements with Z>5or throughout nearly the whole x-ray region,and a is thefine-structure constant given bya¼2p e2hcð17aÞThe theory of x-ray spectra reveals the existence of a limited number of allowed transitions;the rest are‘‘forbidden.’’The most intense lines create the electric dipole ra-diation.The transitions are governed by the selection rules for the change of quantum numbers:D l¼Æ1;D j¼0orÆ1ð18ÞThe j transition0?0is forbidden.According to Dirac’s theory of radiation(Dirac,1947),transitions that are forbidden as dipole radiation can appear as multipole radiation(e.g.,as electric quadrupole and magnetic dipole transitions).The selection rules for the former areD l¼0orÆ2;D j¼0;Æ1;orÆ2ð19ÞThe j transitions0?0,12?12,and0$1are forbidden.The selection rules for magnetic dipole transitions areD l¼0;D j¼0orÆ1ð20ÞThe j transition0?0is forbidden.The commonly used terminology of energy levels and x-ray lines is shown in Figure3.A general expression relating the wavelength of an x-ray characteristic line with the atomic number of the corresponding element is given by Moseley’s law(Moseley,1914): 1¼kðZÀsÞ2ð21Þlwhere k is a constant for a particular spectral series and s is a screening constant for the repulsion correction due to other electrons in the atom.Moseley’s law plays an important role in the systematizing of x-ray spectra.Appendix II tabulates the energies and wave-lengths of the principal x-ray emission lines for the K,L,and M series with their ap-proximate relative intensities,which can be defined either by means of spectral line peak intensities or by area below their intensity distribution curve.In practice,the relativeFigure3Commonly used terminology of energy levels and x-ray lines.(From Sandstro m,1957.)intensities of spectral lines are not constant because they depend not only on the electron transition probability but also on the specimen composition.Considering the K series,the K a fraction of the total K spectrum is defined by the transition probability p K a,which is given by(Schreiber and Wims,1982)p K a¼IðK a1þK a2ÞIðK a1þK a2ÞþIðK b1þK b2Þð22ÞWernisch(1985)proposed a useful expression for the calculation of the transition prob-ability p K a for different elements:p K a;i¼1:052À4:39Â10À4Z2i;11Z i190:896À6:575Â10À4Z i;20Z i291:0366À6:82Â10À3Z iþ4:815Â10À5Z2i;30Z2i608<:ð23ÞFor the L level,split into three subshells,several electron transitions exist.The transition probability p L a,defined as the fraction of the transitions resulting in L a1and L a2radiation from the total of possible transitions into the L3subshell,can be calculated by the ex-pression(Wernisch,1985)p L a;i¼0:944;39Z i44À4:461Â10À1þ5:493Â10À2Z iÀ7:717Â10À4Z2iþ3:525Â10À6Z3i;45Z i828<:ð24ÞRadiative transition probabilities for various K and L x-ray lines(West,1982–83)are presented in detail in Appendix III.The experimental results,together with the estimated 95%confidence limits,for the relative intensity ratios for K and L x-ray lines for selected elements with atomic number from Z¼14to92have been reported by Stoev and Dlouhy (1994).The values are in a good agreement with other published experimental data.Because the electron vacancy created in an atom by charged particles or electro-magnetic radiation has a certain lifetime,the atomic levels E1and E2[Eq.(16)]and the characteristic x-ray lines are characterized by the so-called natural widths(Krause and Oliver,1979).The natural x-ray linewidths are the sums of the widths of the atomic levels involved in the transitions.Semiempirical values of the natural widths of K,L1,L2and L3 levels,K a1and K a2x-ray lines for the elements10Z110are presented in Appendix IV.Uncertainties in the level width values are from3%to10%for the K shell and from 8%to30%for the L subshell.Uncertainties in the natural x-ray linewidth values are from 3%to10%for K a1;2.In both cases,the largest uncertainties are for low-Z elements (Krause and Oliver,1979).C.X-ray SatellitesA large number of x-ray lines have been reported that do notfit into the normal energy-level diagram(Clark,1955;Kawai and Gohshi,1986).Most of the x-ray lines,called satellites or nondiagram lines,are very weak and are of rather little consequence in ana-lytical x-ray spectrometry.By analogy to the satellites in optical spectra,it was supposed that the origin of the nondiagram x-ray lines is double or manyfold ionization of an atom through electron impact.Following the ionization,a multiple electron transition results in emission of a single photon of energy higher than that of the characteristic x-rays.The majority of nondiagram lines originate from the dipole-allowed deexcitation of multiply。
野生兜兰菌根真菌对带叶兜兰生长和生理指标的效应
热带亚热带植物学报2022, 30(1): 88 ~ 96Journal of Tropical and Subtropical Botany野生兜兰菌根真菌对带叶兜兰生长和生理指标的效应陈宝玲, 杨开太*, 龚建英, 唐庆, 苏莉花, 汪小玉, 龙定建(广西壮族自治区林业科学研究院，南宁530002)摘要：为探究兰科菌根真菌对带叶兜兰(Paphiopedilum hirsutissimum)生长的影响，用4个分离自广西野生兜兰根部的兰科菌根真菌(Cladosporium perangustum、Kirschsteiniothelia tectonae、Phialophora sp.和Cyphellophora sp.)与带叶兜兰试管苗和营养钵苗进行菌-苗共生试验，对其生长和生理指标的变化进行了研究。
结果表明，接菌处理具有明显的促进生长作用和生理效应，Cladosporium perangustum和Phialophora sp.对试管苗的接种效果最佳，鲜质量增量、3种保护酶活性和叶绿素总量均与对照存在显著或极显著差异，鲜质量增加了360%~380%。
Kirschsteiniothelia tectonae、Phialophora sp.对营养钵苗的接种效果最佳，鲜质量增量、叶面积及3种保护酶活性均与对照存在显著或极显著差异，鲜质量增加了261%~330%。
因此，实际生产中可在带叶兜兰不同生长阶段接种适当菌株，Phialophora sp.对带叶兜兰表现出较好的促生效应，可研发为带叶兜兰育苗期通用型有益菌剂。
关键词：带叶兜兰；兰科菌根真菌；生理特性；保护酶doi: 10.11926/jtsb.4411All Rights Reserved.Effects of Wild Paphiopedilum Mycorrhizal Fungi on Growth andPhysiological Indexes of Paphiopedilum hirsutissimum SeedlingsCHEN Baoling, YANG Kaitai*, GONG Jianying, TANG Qing, SU Lihua, WANG Xiaoyu,LONG Dingjian(Guangxi Zhuang Autonomous Region Forestry Research Institute,Nanning 530002, China)Abstract: To investigate the effects of mycorrhizal fungi on the growth of Paphiopedilum hirsutissimum, fourstrains, such as Cladosporium perangustum, Kirschsteiniothelia tectonae, Phialophora sp. and Cyphellophora sp.,isolated from roots of wild Paphiopedilum, were inoculated to tissue-cultured and potting seedlings of P.hirsutissimum for 120 days, and then the changes in growth and physiological characters were studied. The resultsshowed that the biomass and physiological indexes of tissue-cultured seedlings increase inoculated withCladosporium perangustum and Phialophora sp., the fresh weight, activities of three protective enzymes, andtotal chlorophyll content had significant differences compared with the control. Especially the fresh weight wasmore than control for 360%-380%. Two strains, Kirschsteiniothelia tectonae and Phialophora sp. had the besteffect for the potting seedlings, which the fresh weight, leaf area, and activities of three protective enzymes hadsignificant difference compared with the control, and the fresh weight increased 261%-330% than control.Therefore, appropriate strains could be inoculated to P. hirsutissimum at different growth stages in actualproduction. Phialophora sp., which showed a good promoting effect on P. hirsutissimum, could be developed as a收稿日期: 2021-03-12 接受日期: 2021-06-03基金项目:广西自然科学基金项目(2020GXNSFAA259028); 广西重点研发计划项目(桂科AB18221003)资助This work was supported by the Project for Natural Science in Guangxi (Grant No.2020GXNSFAA259028); and the Project for Key Research & Developmentin Guangxi (Grant No. AB18221003).作者简介: 陈宝玲(1981~ )，高级工程师，硕士，主要从事兰科植物的保育与繁育研究工作。
同步辐射X-射线衍射技术在材料化学教学中的引入探索
大 学 化 学Univ. Chem. 2024, 39 (3), 29收稿：2023-08-17；录用：2023-09-28；网络发表：2023-11-10*通讯作者，Email:****************.cn基金资助：南开大学“魅力材料”教育教学改革项目•专题• doi: 10.3866/PKU.DXHX202308060 同步辐射X-射线衍射技术在材料化学教学中的引入探索李伟1,*，冯国强2，常泽11南开大学材料科学与工程学院，天津 3003502湖北第二师范学院物理与机电工程学院，武汉 430205摘要：X-射线衍射是表征材料结构的一类重要技术，在材料化学教学中具有举足轻重的地位。
随着新型材料的不断发现，相应的先进X-射线衍射技术也应运而生。
本文基于当前材料化学学科前沿，对高压同步辐射X-射线衍射技术、微焦斑X-射线衍射技术和同步辐射X-射线对分布函数三种先进技术进行介绍，旨在加深学生理解X-射线衍射相关基础知识的同时，能够拓宽科研视野，并提高解决问题的能力。
关键词：X-射线衍射；高压；微焦斑；对分布函数中图分类号：G64；O6Teaching Reform of X-ray Diffraction Using Synchrotron Radiation in Materials ChemistryWei Li 1,*, Guoqiang Feng 2, Ze Chang 11 School of Materials Science and Engineering, Nankai University, Tianjin 300350, China.2 Department of Physics and Mechanical & Electrical Engineering, Hubei University of Education, Wuhan 430205, China.Abstract: X-ray diffraction is a pivotal technique for material structure analysis, playing a fundamental role in materials chemistry. In light of the continuous discovery of novel materials, advanced X-ray diffraction methods have emerged at the forefront of materials chemistry. This paper introduces a teaching reform incorporating three advanced X-ray techniques into materials chemistry instruction: high-pressure synchrotron X-ray diffraction, micro-focus X-ray diffraction, and X-ray pair distribution function analysis. We anticipate that such a teaching reform will empower students to deepen their grasp of X-ray diffraction techniques, broaden their academic horizons, and refine their problem-solving skills.Key Words: X-ray diffraction; High-pressure; Micro-focus; Pair distribution function1 引言X-射线衍射(XRD)技术作为一种重要的结构表征手段，在材料化学研究中得到了非常广泛的应用。
欧洲药典7.5版
INDEX
To aid users the index includes a reference to the supplement in which the latest version of a text can be found. For example : Amikacin sulfate...............................................7.5-4579 means the monograph Amikacin sulfate can be found on page 4579 of Supplement 7.5. Note that where no reference to a supplement is made, the text can be found in the principal volume.
English index ........................................................................ 4707
Latin index ................................................................................. 4739
EUROPEAN PHARMACOPபைடு நூலகம்EIA 7.5
Index
Numerics 1. General notices ................................................................... 7.5-4453 2.1.1. Droppers...................
氧化镧中放射性的检测和去除
2017·53·Fig.1Standard curve of V.Table1Concentration of V in saline lake water.Saline lake watersample 1st Conc.ofV/(µg/L)2nd Conc.ofV/(µg/L)3rd Conc.ofV/(µg/L)4th Conc.ofV/(µg/L)Meanconc.ofV/(µg/L)RSD/%Sample121.9823.2723.1224.4423.20 4.3Sample2 3.33 3.47 3.66 3.45 3.47 3.9Sample37.267.37 6.937.287.21 2.6References[1]M.P.Zheng,X.F.Liu,Acta Geologica Sinica,84(11)(2010)1585.[2]X.J.Yin,J.Bai,W.Tian,et al.,J Radioanal Nucl.Chem.,313(2017)113.[3]X.Y.Min,J.X.Xu,L.M.Li,et al.,Journal of Salt Lake Research,20(2012)18.[4]U.S.Environmental Protection A EPA method200.8,determination of trace metals in waters and wastes by inductivelycoupled plasma-mass spectrometry[S]A:(1994).[5]X.R.Wang.Examples of Inductively Coupled Plasma Mass Spectrometry[M].Beijing:Chemical Industry Press,(2005).2-27Detection and Removal of Radioactivity fromLanthanum OxideChen Desheng1,2and Qin Zhi1(1.Institute of Modern Physics,Chinese Academy of Sciences,Lanzhou730000,China;2.University of Chinese Academy of Sciences,Beijing100049,China)Rare earth elements(REEs)play increasingly critical roles in the transition to green economy.China rank the first in rare earth reserves,output and export volume.However,radioactive elements such as uranium,thorium, radium and actinium etc,accompanied with REEs,so the separation of radioactive elements from REEs is a crucial point in rare earth industry.For the problem that lanthanum oxide products hold excess radioactivity,the production process should be improved.In this study,first,HPGe-γspectrometer was used to determine lanthanum oxide,and identified the radioactivity caused by the existence of227Ac and her decay daughters.Then the extraction performance of La3+ and Ac3+in hydrochloric acid medium was investigated by using2-ethylhexyl phosphate mono-2-ethylhexyl ester (P507)as extractant.When experimental conditions are as follows:the saponification degree of P507:30%,the acidity of the feed solution:pH=2.45,the La3+concentration:32g/L,and the salting-out agent KNO3concentration:3 mol/L,the extraction and separation properties of La3+and Ac3+are better.With the optimized experimental conditions,the low radioactivity of lanthanum oxide is obtained.Figure.1 shows the comparison of alpha radioactivity in unpurified and purified lanthanum oxide and after113h,the radioactivity in purified lanthanum oxide reduce significant,and calculated the removal ratio of227Ac in lanthanum oxide is approximately89.97%.These conclusions have practical significance for the removal of radioactivity from lanthanum oxide.·54·2017Fig.1(color online)(a)Comparison of alpha radioactivity in unpurified and purified lanthanum oxide;(b)Comparison of alpha radioactivity in unpurified and purified lanthanum oxide after113h.。
XRD patterns 1c.宾夕法尼亚大学
2. peak intensities - how much?
3. peak shape 4. background structure
peak positions
Quantitative analysis Example: 2-phase mixtures of CaF2 & ZnO
CaF2
Iia =
KiaXa ρa µ
Quantitative Analysis
Use measured intensities ….. but not simple
Main equation for quantitative analysis
Iia = intensity of reflection i of phase a
Why index?
It can be fun! Like solving a puzzle Indices needed to calculate lattice parameters need (hkl) and dhkl for all reflections use all reflections to get high precision cubic: dhkl2 = a2/(h2 + k2 + l2) tetragonal: 1/dhkl2 = (h2 + k2)/a2 + l2 /c2 hexagonal: 1/dhkl2 = (4/3)(h2 + k2 + hk)/a2 + l2 /c2 orthorhombic: 1/dhkl2 = h2/a2 + k2/b2 + l2 /c2 etcetera
1. 2. 3. 4. peak positions peak intensities peak shape background structure
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a r X i v :a s t r o -p h /9707086v 2 21 J u l 1997Hard X-ray Emission from Cassiopeia A SNRLih-Sin The ∗,Mark D.Leising ∗,Dieter H.Hartmann ∗,James D.Kurfess †,Philip Blanco §,and Dipen Bhattacharya ‡∗Department of Physics and Astronomy,Clemson University,Clemson,SC 29634-1911†E.O.Hulburt Center for Space Research,Naval Research Laboratory,Code 7650,Washington,DC 20375-5352§Center for Astrophysics and Space Sciences,University of California,San Diego,CA 92093‡Institute of Geophysics and Planetary Sciences,University of California,Riverside,CA 92521Abstract.We report the results of extracting the hard X-ray continuum spectrum of Cas A SNR from RXTE/PCA Target of Opportunity observations (TOO)and CGRO/OSSE observations.The data can rule out the single thermal bremsstrahlung model for Cas A continuum between 2and 150keV.The single power law model gives a mediocre fit (∼5%)to the data with a power-law index,Γ=2.94±0.02.A model with two component (bremsstrahlung +bremsstrahlung or bremsstrahlung +power law)gives a good fit.The power law index is quite constrained suggesting that this continuum might not be the X-ray thermal bremmstrahlung from accelerated MeV electrons at shock fronts [1]which would have Γ≃2.26.With several SNRs detected by ASCA showing a hard power-law nonthermal X-ray continuum,we expect a similar situation for Cas A SNR which has Γ=2.98±0.09.We discuss the implication of the hardest nonthermal X-rays detected from Cas A to the synchrotron radiation model.INTRODUCTIONX-ray observations of supernova remnants have been stimulated by recent re-ports of nonthermal power-law X-ray detections suggesting supernovae as sites of charged particle accelerations and sources of cosmic rays.The first strong evidence for charged particle acceleration near supernova shock fronts in the X-ray energy band is demonstrated by the morphological and spectral correlation between X-ray and radio emission from the bright NE and SW rims of SN 1006[2].The brightest radio emission regions show almost featureless power law X-ray spectra when com-pared with SN 1006central region which is dominated by emission lines of highly ionized elements in a non-equilibrium ionization thermal plasma.The nonthermal X-ray component has been modeled as a synchrotron emission from electrons ac-FIGURE1.The thermal bremsstrahlung(kT=7.93keV;dashed line)+power-law(Γ=2.98; dashed-dotted line)+6K X-ray line model produces a goodfit(solid line)to the PCA&OSSE data(crosses)with aχ2/dof=1.077,dof=62.celerated to∼100TeV within shock fronts[3–5].In this model,the radio spectrum is produced by synchrotron radiation of electrons accelerated to∼GeV energies with the radio power-law index being less steep than the X-ray power-law index. Several similar evidences also have been demonstrated by ASCA measurement of RX J1713.7-3946[6]and IC443[7],and RXTE and OSSE measurements of Cas A [8–10].OSSE with a total accumulation time of15×105detector-seconds,detected a hard continuum between40-150keV from Cas A SNR at a4σconfidence with a flux of∼9×10−7γcm−2s−1keV−1at100keV[10].The detection is the hardest X-ray detection from a SNR without plerionic source.However,the shape of the continuum has not been strongly constrained.The continuum can either be a bremsstrahlung with kT≃35keV or a power law withΓ≃3.06.In this paper,we use the2-30keV RXTE/PCA TOO and the40-150keV CGRO/OSSE Cas A data to better determine the shape of Cas A hard X-ray continuum.RESULTSThe RXTE/PCA data used in this analysis is the TOO by RXTE on Aug.2, 1996with a total observing time of∼4000sec.Wefit the2-30keV PCA data simultaneously with the40-150keV OSSE data.The results offitting several models with one or two continuum plus about six emission lines from Si,S,Ar,Ca, and Fe are shown in Table1.The line widths arefixed to100eV and the hydrogen column density toward Cas A isfixed at1×1022H cm−2[11,12].Wefind that a single thermal bremsstrahlung model for the data can be ruled out.Nevertheless, a single power law model gives a mediocrefit.We alsofind the two models that bestfit the EXOSAT[12]and Tenma[11]data cannot give acceptablefits to the PCA and OSSE data.A two component model,either the bremsstrahlung+ bremsstrahlung or the bremsstrahlung+power law,each gives an equally good fit.In Figure1for the current interest in a nonthermal power law model,we show the result of the thermal bremsstrahlung+power-law modelfit to the data.The power law continuum is detected with a higher confidence level and the power-law index is more tightly constrained than using the OSSE data alone[10].The PCA and OSSE data is consistent only at a3.8%level with the X-ray bremsstrahlung from accelerated MeV electrons at shock fronts as suggested by Asvarov et al.[1] which would haveΓ=α+1.5=2.26whereαis the radio spectral index.FIGURE2.The synchrotron photon energy relation with the electron energy[2]for Cas A(solid line),IC443(dashed line),and SN1006(dashed-dotted line).The solid squares and the open squares mark the maximum electron energy constrained by the synchrotron energy loss(Eq.(1) of[4])for f*R J=1and f*R J=10,respectively.The solid triangles and the open triangles mark the maximum electron energy bounded by the age of the SNRs(Eq.(2)of[4])for f*R J=1and f*R J=10,respectively.This maximum energy is shown only for SN1006due to its low magnetic field.Synchrotron energy loss sets the maximum electron energy in Cas A and IC443.The shock speed is assumed to be5000km/s in each case.f is the ratio of the electron mean free path to the electron gyroradius.R J is the factor that contains the orientation of the shock relative to the magneticfield.The dotted lines shows some interesting synchrotron photon energies at1GHz, 10keV,and100keV.A summary of the detected nonthermal continuum from four SNRs is shown in Table2.Cas A is of interest because from the4SNRs with measured nonther-mal power-laws,it is the youngest,has the strongest magneticfield,its detected nonthermal energy is the highest,and it has the steepest X-ray and radio power-law indexes,of four SNRs with measured nonthermal power law.In Figure2,we show for Cas A,IC443,and SN1006how close their detected hard X-ray energies to the maximum synchrotron energies.The synchrotron energy is related to the maximum electron energy which is limited by the synchrotron energy loss and the SNR’s age.Cas A,as the brightest radio SNR source,has the most intense mag-neticfield and therefore it causes the large synchrotron energy loss which limits Cas A’s maximum electron energy.Figure2shows that the hard X-ray emission detected from Cas A by OSSE is near the cutoffsynchrotron energy or indirectly to the maximum electron energy.Further Cas A measurements by OSSE may detectparison of the measured nonthermal continuumSN10069713-10µG0.560.5-20 2.95RX J1713.7-3946≥1000??0.5-10 2.45IC4431000500µG<0.240.5-12 2.35Cas A3171-5mG0.7615-150 2.98the cutoffenergy and hence would provide the evidence that the nonthermal power law emission is the synchrotron radiation from accelerated electrons at the shock fronts near the maximum energy.Another evidence of the synchrotron radiation being the process for the nonthermal emission is the steepening of spectral index from radio to X-ray energy.It has been suggested that the turnover or break∼0.25 keV is observed in SN1006spectra[5].We expect the turnover in Cas A spectra is∼1-10keV due to Cas A’s strong magneticfield.However,in order to observe this turnover in Cas A spectra,an X-ray imaging detector is needed because Cas A’s thermal bremsstrahlung contributes substantially near this energy.REFERENCES1.Asvarov,A.I.,Guseinov,O.Kh.,Dogel,V.A.,Kasumov,F.K.,Soviet 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