核能专业英语试卷库

核能专业英语试题（A卷）
考试时间：90分钟
姓名：班级：学号：
The most elementary concept is that matter is composed of individual particles – atoms – that retain their identity as elements in ordinary physical and chemical interactions. Thus a collection of helium atoms that forms a gas has a total weight that is the sum of the weights of the individual atoms. Also, when two elements combine to form a compound, the total weight of the new substance is the sum of the origin elements.
1.公认的物质的概念是：物质是由单个粒子——原子组成，在普通的化学和物理反应
中原子保持了元素的特性。

因此，因此一团由氦原子组成的气体的重量就是其中每一个原子重量的总和。

同样，当两种元素结合成化合物时，新物质的总重量是原先的元素的质量之和。

Bohr assumed that the atom consists of a single electron moving at constant speed in a circular orbit about a nucleus --the proton--as sketched in Fig. X.X. Each particle has an electric charge of l.6×l0-l9 coulombs, but the proton has a mass that is 1836 times that of the electron.
2.波尔假设（氢）原子由一个单独的电子绕着一个核子——质子，以圆形轨道作恒定
速度的移动——见图X.X，每个粒子有l.6×l0-l9库伦的电量，质子的质量是电子质量的1836倍。

Most elements are composed of particles of different weight, called isotopes. The nucleus of ordinary hydrogen is the positively charged proton; the deuteron consists of a proton plus a neutron, a neutral particle of weight very close to that of the proton; the triton contains a proton plus two neutrons.
3.大多数元素是由重量不同的粒子构成，我们称之为“同位素”。

普通氢的原子核是一
个带正电的质子；氘核由一个质子加一个重量十分接近质子的中性粒子（中子）组成；氚核则是由一个质子加两个中子组成。

The number of disintegrations per second (dis/sec) of a radioisotope is called the activity, A. Since the decay constant λ is the chance of decay each second of one nucleus, for N nuclei the activity is the product A = λ N. The unit dis/sec is called the becquerel (Bq), honoring the scientist who discovered radioactivity. Another older and commonly used unit of activity is the curie (Ci) named after the French scientists Pierre and Marie Curie who studied radium. The curie is 3.7 ⨯1010 dis/sec.
4.放射性同位素每秒衰变的原子数称为活度（记作A）。

既然衰变常数λ是核子每秒
衰变的几率，N个核子的活度是乘积A=λN。

单位dis/sec称为“贝克勒尔”（Bq），用来纪念这位发现放射性活度的科学家。

另一个更早的曾被普遍使用的放射性活度的单位是“居里”（Ci），这是以研究镭的法国科学家皮埃尔和玛丽·居里的名字命
名的。

1居里等于3.7 ⨯1010贝克。

Nuclear reactions may take place spontaneously, as in radioactivity, or may be induced by bombardment with a particle or ray. Nuclear reactions are much more energetic than chemical reactions, but they obey the same physical laws---conservation of momentum, energy, number of particles, and charge.
5.核反应（有原子核参与）可能会自然发生，如放射性，或可能被粒子或射线轰击诱发。

核
反应比化学反应剧烈的多，但它们遵守同样的物理定律-----动量、能量、粒子数、电荷守恒。

Since the neutron is a neutral particle it does not experience electrostatic repulsion and can readily penetrate a target nucleus. Neutrons are thus especially useful as projectiles to induce reactions.
6.因为中子是中性的粒子，它不受静电排斥所以能够轻易穿透靶核。

中子作为入射粒子诱发
的反应时非常有用的。

We now turn to a group of three related processes involving gamma ray photons produced by nuclear reactions. These have energies as high as a few MeV. The interactions include simple scattering of the photon, ionization by it, and a special nuclear reaction known as pair production.
A.Photon-Electron Scattering
B.Photoelectric Effect
C.Electron-Positron Pair Production
7.现在我们转向于与核反应产生的γ射线光子有关的三个过程，这些光子的能量可达几兆电
子伏。

反应包括简单的光子散射、电离，以及众所周知的一个特殊核反应——电子对效应。

A.光电散射
B.光电效应
C.电子对产生效应
Out of many nuclear reactions known, that resulting in fission has at present the greatest practical significance. In this chapter we shall describe the mechanism of the process, identify the byproducts, introduce the concept of the chain reaction, and look at the energy yield from the consumption of nuclear fuels.
8.目前，在许多已知的核反应中，导致裂变的反应最有实用意义。

在这一章中我们将描述这
一过程的机制，认识其副产物，介绍链式反应的概念，搞清楚从核燃料的消耗中产出的能量。

In the “hydrogen bomb”, the high temperatures created by a fission reaction cause the fusion reaction
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to proceed in a rapid and uncontrolled manner. Between these extremes (极端的状况) is the possibility of achieving controlled fusion reaction that utilizes (利用) inexpensive and abundant fuels.
9. 在氢弹中，裂变反应产生的高温导致聚变以迅速和不可控的方式进行。

在这些极端
的状况之间的是利用廉价且丰富的燃料实现聚变反应的可能。

A major step toward higher particle energies resulted from the invention of the synchrotron. It consists of the periodic acceleration of the particles by radio-frequency electric fields, but with a time-varying magnetic field that keeps the charges on a circular path. Ions (that are out of step) are brought back into step, i.e., they are synchronized.
10. 向着更高粒子能迈进的主要一步应归功于同步加速器的发明。

同步加速器由使粒子
产生周期性加速的高频电场，以及为保持电荷作圆周运动而随时间变化的磁场组成。

同步加速器使步调不一致的离子被带回到同步。

Substances in the gaseous state (气态) are described approximately by the perfect gas law 理想气体规律(方程), relating pressure, volume, and absolute temperature (绝对温度), pV=nkT.
An increase in the temperature of the gas due to heating causes greater molecular motion, which results in an increase of particle bombardment (n 炮击；轰击) of a container wall and thus of pressure on the wall.
The particles of gas, each of mass m , have a variety of(多种的) speeds v in accord with 与……一致Maxwell’s gas theory (麦克斯韦气体理论) as shown in Fig. 2.1.
11. 气态的物质可以用与压力、体积和绝对温度有关的理想气体规律方程pV=nkT 来近
似地描述。

温度上升将引起分子运动的加剧——从而引起粒子对容器内壁的碰撞的增加而导致其压力的增大。

每种质量（m ）的气体粒子具有的不同速度与图2.1所示的麦克斯韦理论一致。

The most probable speed(最概然速率), at the peak of Maxwellian distribution (麦克斯韦分布) , is dependent on temperature according to the relation (关系式)…….
The kinetic theory of gas ( 气体动力学) provides a basis for calculating properties such as the specific heat (比热).
Using the fact from Chapter l that the average energy of gas molecules is proportional (成比例
的) to the temperature, , we can deduce (推想), that the specific heat of a gas consisting only of atoms is , where m is the mass of one atom.
从麦克斯韦分布图上可以看到，在其峰值处出现的气体粒子的最概然速率，按照这个关系式……，是与温度紧密相关的。

气体动力学为计算诸如比热之类的一些性质提供了基础。

用第一章中气体分子的平均能量正比于温度的事实， ，我们可以推断出单元子气体的
比热 ，在公式中m 是一个原子的质量。

Until the 20th century the internal structure of atoms was unknown, but it was believed that electric charge (电荷) and mass were uniform (统一的). Rutherfor performed (执行) some crucial (至关紧要的) experiments in which gold atoms were bombarded by charged particles. He deduced (推断)in 1911 that most of the mass and positive charge （正电荷） of an atom were concentrated (集中的) in a nucleus of radius only about l0-5 times that of the atom, and thus occupying a volume of about 10 - l5
times that of the atom. The new view of atoms paved the way for (为…铺平道路) Bohr to find an explanation for the production of light.
12. 直到20世纪，原子的内部结构仍然是未知的，但是人们确信核电荷数与原子质量是相同
的。

卢瑟福进行了一些重要的实验，包括用带电粒子轰击金原子。

他在1911年推断出：原子的质量和正电荷都集中在半径为l05分之一的原子大小的原子核，因此占原子体积为10l5分之一。

关于原子的新观点为波尔解释光的产生铺平了道路。

The electronic structure of the other elements is described by the shell model (壳模型), in which a limited number of electrons can occupy a given orbit or shell. The atomic number Z is unique (独特的) for each chemical element, and represents (描绘) both the number of positive charges on the central massive (结实的) nucleus of the atom and the number of electrons in orbits around the nucleus.
The chemical behavior of elements is determined by the number of electrons in the outermost (最外面的) or valence (原子价) shell.
13. 其它元素的电子模型是用壳模型来描述的，一定限制数量的电子能够占据一个给定的轨道
或壳层。

对每一个化学元素，原子序数Z 是唯一的，它代表了原子中央结实核子的正电荷数以及围绕核子的轨道的电子数。

最外层的电子数或化合价层，决定了元素的化学性质。

14. Ordinary light as in the visible range (可见区) is a mixture of many frequencies, directions, and
phases(状态). In contrast, light from a laser (“Light Amplification by Stimulated Emission of Radiation” ) consists of a direct beam of one color and with the waves in step (相干).
15. Lasers can be constructed from several materials. The original one (1960) was the crystalline
gem ruby (水晶红宝石). Others use gases such as a helium-neon(氦-氖) mixture, or liquids with dye in them, or semiconductors(半导体 ).
16. Lasers are widely used where an intense (强烈的) well-directed beam is required, as in metal
cutting and welding, eye surgery (眼部外科手术) and other medical applications, and accurate surveying and range finding(精确的测量和测距). Newer applications are noise-free phonographs (无噪声留声机, 电唱机), holograms (全息摄影) ( 3D images), and communication between airplane and submarine (潜水艇).
3
2E kT =32
c k m =3
2
c k m =3
2E kT =
17.普通光，例如可见光区，是由许多频率、方向和状态不同的光混合而成的。

相对的
是，激光是由同一方向的单一颜色的光束组成，而且是相干波。

激光的产生可以来源于多种材料。

最早的一种是1960年使用的水晶红宝石。

其它的还可以用气体（如氦-氖混合气体），或者染料液体，以及半导体来做激光发生器。

激光可以被广泛地应用于需要良好方向性光/热束的地方，例如金属的切割与焊接，眼部外科手术及它医疗应用还有精确的测量和测距上。

新出现的应用还包括无噪声留声机、全息摄影以及飞机和潜艇的通讯。

Most elements are composed of particles of different weight, called isotopes (同位素). For instance, hydrogen has three isotopes of weights in proportion l, 2, and 3 -ordinary hydrogen, heavy hydrogen (deuterium氘), and tritium(氚).
The nucleus of ordinary hydrogen is the positively charged proton(带正电的质子); the deuteron(氘核)consists of a proton plus a neutron, a neutral particle(中性粒子) of weight very close to that of the proton; the triton(氚核) contains a proton plus two neutrons.
18.大多数元素是由重量不同的粒子构成，我们称之为“同位素”。

例如：氢元素有三种
同位素，原子量比为1：2：3——普通氢（氕）、重氢（氘）以及超重氢(氚)。

普通氢的原子核是一个带正电的质子；氘核由一个质子加一个重量十分接近质子的中性粒子（中子）组成；氚核则是由一个质子加两个中子组成。

The force of electrostatic repulsion (静电排斥) between like charges (同种电荷), which varies inversely (相反地) as the square of their separation, would be expected to be so large nuclei could not be formed. The fact that they do exist is evidence (证明) there is an even larger force of attraction. The nuclear force (核力) is of very short range, as we can deduce from(从…推论出) the above rule of thumb. The nuclear force acts only when the nucleons are very close to each other, and binds them into a compact structure (紧凑结构). Associated with the net force is a potential energy of binding(结合势能).
19.同种电荷之间的静电斥力随着它们距离的平方成反比变化，可以想见其会大到核子
无法形成的地步。

我们可以凭经验推断出——核力的作用范围一定非常短的。

只有当核子之间靠得很近时，核力才起作用将它们紧密地结合在一起。

与这种合力相关的是结合势能。

20.The rate at which a radioactive substance disintegrates (and thus the rate of release of
particles) depends on the isotopic species(种类，核素), but there is a definite (一定的) “decay law” that governs(管理,支配) the process. In a given time period, say one second, each nucleus of a given isotopic species has the same chance of decay. If we were able to watch one nucleus, it might decay in the next instant (立即的), or a few days later, or even hundreds of years later.
3、放射性物质的衰变率（粒子释放率）决定于同位素的种类，但是也确定存在着“衰变规律”支配着这个过程。

在一个给定的时间段，譬如一秒，给定同位素的每个核子都具有相同的衰变几率。

如果我们能对某个核子进行观察的话，它可能在下一个瞬间发生衰
变，也有可能在几天甚至几百年以后才发生衰变。

21.Such statistical(统计学的) behavior is described by a constant property of the atom called
half-life (半衰期). This time interval(间隔), symbolized by t H is the time required for half of the
nuclei to decay, leaving half of them intact(完整无缺的). We should like to know how many
nuclei of a radioactive species remain at any time. If we start at time zero with N0 nuclei, after a
length of time t H there will be N0/2; by the time 2t H has elapsed (流逝), there will be N0/4; etc. A
graph of the number of nuclei as a function of time is shown in Fig. 3.l.
4、这种统计学上的表现可以用原子的一个恒定属性——半衰期来表示。

这个用t H 表示的时间
间隔指的是一半的核子发生衰变所需要的时间。

我们想知道在任意时间放射性核素的剩余量。

如果在一开始有N0 个核子，那么经过了t H的时间以后，核子还剩下N0/2 个；经过2t H 时，核
子还剩下N0/4个……核子数与时间的函数关系可以用图3.l来表示。

Finding the half-life of an isotope provides part of its identification (鉴定), needed for beneficial
use or for protection against radiation hazard. Let us look at a method for measuring the half-life
of a radioactive substance. As in Fig. 3.2, a detector 探测器(that counts the number of particles
striking it ) is placed near the source of radiation (放射源).
8、为了有益的应用或者是为防止辐射危害而需鉴定放射性核素，而找出它的半衰期，则可为
鉴定同位素提供线索。

让我们来看看一种检测放射性物质半衰期的方法。

如图3.2所示，一个
探测器（统计击打到它上的粒子数）放置在放射源的附近。

From the number of counts observed in a known short time interval, the counting rate (计数率)is
computed. It is proportional to the rates of emission of particles or rays from the sample and thus
to the activity A of the source. The process is repeated after an elapsed time for decay. The
resulting values of activity are plotted on semi-log graph paper (半对数坐标纸) as in Fig. 3.3,
and a straight line drawn through the observed points. From any pairs of points on the line λ and
t H = 0.693/λ can be calculated (see Exercise 3-8).
9、计数率可以通过一段时间间隔内的计数计算出来。

计数率与样本发射粒子或射线的速率成
正比，也就是说与活度A成正比。

在衰变发生的一段时间内重复这个过程：把活度的结果标记
在如图3.3那样的半对数坐标纸上，然后画一条直线穿过这些观察点。

从直线上任意两个点可
以计算出λ，这样，半衰期t H = 0.693/λ就求出来了。

The measurement of the activity of a radioactive substance is complicated by the presence (存在)
of background radiation (本底辐射), which is due to cosmic rays (宇宙射线) from outside the
earth or from the decay of minerals in materials of construction (建筑物) or in the earth. It is
always necessary to measure the background counts (本底计数) and subtract (减去) them from
those observed in the experiment.
10、放射性物质活度的测量因“本底辐射”的存在而变得复杂，这源于地球之外的宇宙射线或
来自建材抑或土壤中的矿石的衰变。

我们经常需要测量本底计数并把它们从实验观测计数中减
去。

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Nuclear reactions(核反应)---those in which atomic nuclei participate(参与) ---may take place spontaneously (自然地), as in radioactivity, or may be induced (感应, 诱发) by bombardment (轰击, 撞击) with a particle or ray. Nuclear reactions are much more energetic(精力充沛的, 高能的) than chemical reactions, but they obey the same physical laws---conservation (守恒) of momentum (动量), energy, number of particles, and charge.
1、核反应（有原子核参与）可能会自然发生，如放射性，或可能被粒子或射线轰击诱发。

核反应比化学反应剧烈的多，但它们遵守同样的物理定律-----动量、能量、粒子数、电荷守恒。

The number of possible nuclear reactions is extremely large because there are about 2000 known isotopes and many particles that can either be projectiles (发射体, 入射粒子) or products (产物)---photons, electrons, protons, neutrons, alpha particles, deuteron (氘核), and heavy charged particles(重带电粒子). In this chapter we emphasize (强调, 着重) induced reactions, especially those involving neutrons.
2、可能发生核反应的数量是非常大的，因为有大概2000种已知的同位素以及许多粒子，他们既可是发射体又可能是产物-------光子、电子、质子、中子，α粒子，氘核，重带电粒子。

在这一章中我们强调辐射引发的反应，尤其是包含中子的反应。

The calculations just completed tell us the total kinetic energy of the product particles but do not reveal (显示) how much each has, or what the speeds are. To find this information we must apply the principle of conservation of momentum (动量守恒法则). Recall that the linear momentum (线动量) p of a material particle of mass m and speed v is p= mv.
This relation is correct in both the classical (经典的) and relativistic (相对论的) senses.
The total momentum of the interacting particles before and after the collision is the same.
9、刚才的计算结果求出了产出粒子的总动量但并没有算出其中每一个粒子的动量，或是速度。

我们须用动量守恒法则来算出这些数据。

一个质量为m速度为v的物质粒子的线动量p=mv。

这个关系在经典力学的和相对论的领域都是适用的。

在碰撞前后，这些相互作用的粒子的总动量总是守恒的。

We can perform a set of imaginary experiments that will clarify (阐明) the idea of cross section (截面). Picture, as in Fig. 4.2(a) a tube of end area (截面积) 1 cm2 containing only one target particle. A single projectile is injected(注入) parallel to(平行于) the tube axis, but its exact location is not specified. It is clear that the chance of collision, labeled σ (sigma) and called the microscopic cross section (微观截面), is the ratio of the target area to the area of the tube, which is 1.
10、我们可以进行一套假想的实验来阐明截面的概念。

如图4.2（a）一个截面积为1 cm2的试管仅含有一个靶粒子。

从平行于试管的X轴注入一个入射粒子，但它的准确位置是不确定的。

很明显，一个入射粒子碰撞的几率，即微观截面（记为σ），等于靶面积与试管的截面积的比值。

The cross section for neutron absorption in materials depends greatly on the isotope bombarded and on the neutron energy. For consistent (一致的) comparison and use, the
cross section is often cited (引用) at 0.0253 eV, corresponding to neutron speed 2200m/sec.
The dependence of absorption cross section on energy is of two types, one called l/v, in which σa
varies inversely (相反地) with neutron speed, the other called resonance (共振), where there is a
very strong absorption at certain neutron energies.
16、中子在物质中的吸收截面极大依赖于被轰击的同位素和中子能量。

为了比较和使用上的一
致，通常引用0.0253eV 的截面，相对应的中子速度为2200m/sec。

吸收截面对于能量的依赖有两种类型，一个称1/v，σa与中子速度成反比，另一个叫共振，对一定能量的中子吸收非常强。

We can guess that the larger the neutron speed v and the larger the transport mean free path (平
均自由程)λt,the more neutron flow will take place. Theory and measurement show that if n
varies in the z-direction, the net flow of neutrons across a unit area each second, the net current
density, is
19、我们可以猜到中子的速度v越大平均自由程λt越远，而且将会产生更多的中子流。

理论和
测量显示：如果n在z轴方向发生改变，每秒穿过单位面积的净中子流（净流密度）是
Neutron absorption cross sections (吸收截面) vary (改变) greatly with target isotope and with
neutron energy, while scattering cross sections (散射截面) are relatively constant. Neutrons are
slowed readily by collisions with light nuclei and migrate (移动) from their point of origin. On
reaching thermal energy they continue to disperse (散开), with the net flow dependent on the
spatial variation of flux.
22、中子吸收截面因靶同位素和中子能量改变很大，然而散射截面相对来说是一定的。

中子通
过与轻原子核碰撞轻易减速并从它们的原先位置移开。

继续扩散达到热能，净流量依赖通量的
空间的分布变化。

The word “radiation” will be taken to embrace (包含) all particles, whether they are of material or electromagnetic origin. We include those produced by both atomic and nuclear processes and those
resulting from electrical acceleration, noting that there is no essential (本质的) difference between
X-rays from atomic collisions and gamma rays from nuclear decay; protons can come from a particle
accelerator, from cosmic rays (宇宙射线) , or from a nuclear reaction in a reactor (反应堆). The
word “materials” wil1 refer to (涉及) bulk (大多数) matter, whether of mineral or biological origin,
as well as to the particles of which the matter is composed, including molecules, atoms, electrons,
and nuclei.
1.“辐射”这个词涵盖了所有的粒子，不论他们来自某种物质还是电磁场。

我们如果将那些由
原子和核过程产生的以及那些来自电子加速的粒子加以比较的话，可以发现由原子碰撞产生的
X射线和核子衰变产生的γ射线并没有本质上的区别；质子可以由粒子加速产生，也可以来源
于宇宙射线或反应堆中的核反应。

“物质”这个词涉及大多数物体，无论是矿物质还是生物组
织，也包括组成物质的粒子：分子、原子、电子和核子。

Beta particles as electrons from nuclear reactions have energies in the range 0.0l-l MeV, and thus are capable of (能够) producing large amounts of ionization as they penetrate (穿透) a substance. As
a rough rule of thum
b (经验方法), about 32 eV of energy is required to produce one ion pair (离子
对). The beta particles lose energy with each event, and eventually are stopped. For electrons of l
3
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MeV energy, the range (射程), as the typical distance of penetration, is no more than a few millimeters (毫米) in liquids and solids or a few meters in air.
4.如同来自核反应中的电子，贝塔粒子的能量范围是0.0l-l MeV，并且当它们穿透物质时能够产生大量的电离作用。

粗略地估计，产生一个离子对大概需要32 eV的能量。

贝塔粒子在每次碰撞中都会损失能量，直到最终停下。

对l MeV能量的电子，其射程，即穿透距离，在液体和固体不超过几毫米，在气体中也不过几米远而已。

The probability of Compton scattering (康普顿散射) is expressed by a cross section (截面), which is smaller for larger gamma energies as shown in Fig. 5.4 for the element lead (铅plumbum), a common material for shielding against X-rays or gamma rays. We can deduce (推论) that the chance of collision increases with each successive (逐次的, 相继的) loss of energy by the photon, and eventually the photon disappears.
12.康普顿散射发生的概率可用截面表示，如图Fig. 5.4，对一种常用于防护X射线或γ射线的铅来说，伽马能量越大反应截面越小。

我们可以推断，碰撞几率随着光子能量的持续丧失而上升，最终光子消失。

We are now in a position to understand the connection between neutron reactions and atomic processes. When a high-speed neutron strikes the hydrogen atom in a water molecule, a proton is ejected (逐出), resulting in chemical dissociation (离解, 分裂) of the H2O. A similar effect takes place in molecules of cells in any biological tissue (生物组织). Now, the proton as a heavy charged particle passes through matter, slowing and creating ionization along its path. Thus two types of radiation damage (辐射危害) take place---primary and secondary (初级与次级).
20.我们现在能够理解中子反应和原子反应之间的联系。

当一个高速的中子撞击水分子中的氢原子，一个质子会被逐出，导致H2O的化学分解。

类似的过程发生在任何生物组织的细胞中。

质子作为重带电粒子穿过物质，在慢化过程中产生电离。

因而产生两种辐射危害——初级电离与次级电离。

The reverse process (逆过程) also takes place (Fig. 5.7). when an electron and a positron combine, they are annihilated ( 湮没) as material particles, and two gamma rays of energy totaling at least l.02 MeV are released. That there must be two photons is a consequence of the principle of momentum conservation.
17.当正负电子结合时，逆过程也会发生(如图5.7)，作为物质粒子它们发生湮没，同时发射出的两束总能量至少有l.02 MeV的伽马射线。

根据动量守恒定律的推断，必然有两个（方向相反、能量相等的）光子产生。

Figure 5.4 shows that the total gamma ray cross section curve (曲线) for lead (Pb), as the sum of the components for Compton effect, photoelectric effect, and pair production, exhibits a minimum around 3 MeV energy. This implies that gamma rays in this vicinity (附近) are more penetrating (有穿透力的) than those of higher or lower energy. In contrast with (与…对比) the case of beta particles and alpha particles, which have a definite range (确定的射程), a certain fraction of incident gamma rays can pass through any thickness of material.
18.如图5.4所示铅的伽马射线反应总截面曲线（总截面是康普顿效应，光电效应截面以
及电子对效应截面之和）显示最小截面出现在3 MeV能量处。

这就表明当伽马射线的能量在
3MeV左右时，其穿透力最强。

与有确定的射程的阿尔法粒子和贝塔粒子相比，某些伽马射线
的能够穿透任何厚度的物质。

In Stage A, the neutron approaches (接近) the U-235 nucleus. In Stage B, the U-236 nucleus has been formed, in an excited state (激发态). The excess (过度的, 额外的) energy in some cases may
be released as a gamma ray, but more frequently (常常, 频繁地), the energy causes distortions (变形)
of the nucleus into a dumbbell shape (哑铃形状), as in Stage C. The parts of the nucleus oscillate (振
荡) in a manner analogous to (类似于) the motion of a drop of liquid. Because of the dominance (优
势) of electrostatic repulsion over nuclear attraction, the two parts can separate, as in Stage D. They
are then called fission fragments (裂变碎片), bearing (具有)most of the energy released.
3. 在A阶段，中子接近U-235核。

在B阶段，U-236核形成并处于激发态。

C阶段：在一些
情况下过多的能量以伽马射线的形式释放出来，但更有可能的是，能量导致核子变形成哑铃
状。

，D阶段：核子的各部分的振荡在一定程度上类似于一滴液体的运动。

因为静电斥力大于
核引力，这两个部分可能分离。

它们被称作裂变碎片，具有大部分的释放能。

They fly apart at high speeds, carrying some 166MeV of kinetic energy out of the total of around 200MeV released in the whole process. As the fragments (碎片) separate, they lose atomic
electrons, and the resulting high-speed ions lose energy by interaction with the atoms and molecules
of the surrounding medium. The resultant thermal energy is recoverable (可重获的) if the fission
takes place (发生) in a nuclear reactor. Also shown in the diagram are the prompt (瞬发)gamma rays
and fast neutrons that are released at the time of splitting.
4. 它们带着166MeV的动能以高速飞离，而整个过程中释放的总能量大概是200MeV。

当碎片
分开，它们的原子失去电子，高速运动的离子与周围介质中的原子和分子反应损失能量。

如果
裂变发生在核反应堆中，发出的热能可持续获得。

图表中也显示了分裂时放出的伽马射线和快
中子。

The above calculation did not include any kinetic energy brought to the reaction by the neutron, on the grounds that (由于，因为) fission can be induced by absorption in U-235 of very slow
neutrons. Only one natural isotope (天然同位素), 235U, undergoes (经历) fission in this way, while
239Pu and 233U are the main artificial isotopes (人工同位素) that do so. Most other heavy isotopes
require significantly larger excitation energy to bring the compound nucleus (复合核) to the required
energy level for fission to occur, and the extra energy must be provided by the motion of the
incoming neutron.
6. 因为铀235吸收慢中子可以诱发裂变反应，以上的计算没有包括中子带到反应中的任何动
能。

只有一种天然同位素铀235以及人工同位素中的钚239和铀233U以这种方式发生裂变。

绝大多数其他重同位素需要极大的激发能来使复合核达到发生裂变所需的能量，额外的能量必
须由入射中子的运动提供。

The precise terminology (术语学) is as follows: fissile (裂变的) materials are those giving rise to fission with slow neutrons; many isotopes are fissionable (可裂变的), if enough energy is supplied.
It is advantageous to use fast neutrons--of the order of 1MeV energy--to cause fission. As will be
discussed in Chapter l3, the fast reactor (快堆) permits the “breeding ”(增殖) of nuclear fuel. In a
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