最新放射性核素的衰变规律

（核，放射性）衰变(decay, disintegration)
• 原子核自发放出α、β、γ等粒子的过程 • (of a substance etc.) undergo change by
radioactivity (Oxford) • any process in which a nucleus emits a
• α粒子的实质：高速运动的氦原子核
α衰变的方程
或：
A ZXA Z42Yα
A ZXA Z42Y42He
• 例：
2826 R 2 n2814 P8 oα
注：衰变过程满足质量数守恒、电荷守恒、 能量守恒以及动量守恒
α衰变的衰变能和衰变条件
• 衰变能： Q (m Z m Z 2 m )c2
• 衰变条件：
β- 衰变(negative beta decay)
• 放射性原子核自发放出β- 粒子，变为原子 序数加1而质量数相同的核素的过程
• β- 粒子的实质：高速运动的电子
β- 粒子能谱之谜
β- 粒子能谱之谜
• β- 粒子能谱是连续谱 • 泡利中微子假说 • 费米弱相互作用理论
β- 衰变的方程
A ZX ZA 1Yβν
• property exhibited by certain types of matter of emitting energy and subatomic particles spontaneously. It is, in essence, an attribute of individual atomic nuclei. (EB)
disintegration by which some unstable atomic nuclei spontaneously dissipate excess energy and undergo a change of one unit of positive charge without any change in mass number. • The three processes are electron emission, positron (positive electron) emission, and electron capture.
species of the same chemical element with different masses whose nuclei are unstable and dissipate excess energy by spontaneously emitting radiation in the form of alpha, beta, and gamma rays (EB)
放射线的分类及本质
放射性(radioactivity)
• 原子核自发放出α、β、γ等粒子的性质
• the spontaneous disintegration of atomic nuclei, with the emission of usu. penetrating radiation or particles (Oxford)
（1~3分钟）
α衰变的纲图(decay scheme)
一个问题
• 从Ra-226的衰变纲图看，只有α和γ粒子的 发射，为何在发自镭源的射线（图3-1）中 显示有β粒子的发射？
β衰变
beta decay
β衰变的定义
• β- 衰变、β+ 衰变和电子俘获(EC)的统称 • 同量异位跃迁(isobaric transition) • any of three processes of radioactive
particle or particles or divides into smaller nuclei (Oxford) • 原子核自发的结构或能量转变过程
α衰变
Alpha decay
α衰变的定义
• 放射性原子核自发放出α粒子而变为另一种 原子核的过程
• type of radioactive disintegration in which some unstable atomic nuclei dissipate excess energy by spontaneously ejecting an alpha particle
• Note: a major source of heat in the interior of both the Earth and the Moon is provided by radioactive decay. (EB)
放射性核素(radionuclide)
• 具有放射性的核素 • a radioactive nuclide (Oxford) • a radioactive nuclide (Merriam-Webster) • radioactive isotopBiblioteka Baidu (radioisotope): any of several
放射性核素的衰变规律
目的
• 熟悉各种衰变的特点 • 掌握衰变规律与活度计算 • 了解放射性平衡及放射系
Pierre Curie
• born May 15, 1859, Paris, France died April 19, 1906, Paris
• French physical chemist and cowinner of the Nobel Prize for Physics in 1903. He and his wife, Marie Curie, discovered radium and polonium in their investigation of radioactivity.
(M ZM Z 2M )c2
MZMZ2M
即：只有比较重(A>140)的原子核才可能发 生α衰变
α衰变的对象
• 丰质子的核素
α衰变的动能分配
• α粒子的动能远大于子核的反冲动能 或：衰变能绝大部分被α粒子带走
• 原子核的基态与激发态
• α粒子的能谱是分立的线状谱
• 短射程α粒子与长射程α粒子
讨论和提问