钍阴离子中低能$^{229m}$ Th异构体的内转换
Internal conversion of the low energy $^{229m}$Th isomer in the Thorium anion
摘要：
本文研究了钍负离子（Th $^-$）中低能级核异构体$^{229m}$ Th（$(3/2^+,8.28 \pm 0.17$ eV）的内转换衰变过程。结果表明，该核同分异构体在Th的$6d_{3/2}^37s_{1/2}^2$基态和$6d_{3/2}^2 7s_{1/2}^2 7p_{1/2}^1$激发态的半衰期分别是Th原子的$6d_{3/2}^2 7s_{1/2}^2$基态的$\approx1.5$和$\approx1.1$的1/2.尽管通过额外的$6d_{3/2}$或$7p_{1/2}$电子衰减，阴离子中的IC概率降低。这个违反直觉的结果是一个结果：a）由于在添加额外电子时它们的扩散性的增加，在核附近的$6d_{3/2}$和$7s_{1/2}$波函数的幅度减小，b）由于运动学因子，IC概率的相互补偿，其取决于连续谱中转换电子的能量，如$E_c^{-1/2}$，以及电子波函数振幅的$E_c^{1/4}$增长。
英文摘要：
A process of the decay of the anomalously low lying nuclear isomer $^{229m}$Th$(3/2^+,8.28 \pm 0.17$ eV) in the Thorium anion (Th$^-$) via the internal conversion (IC) channel is studied. We show that the half life of the nuclear isomer in the $6d_{3/2}^37s_{1/2}^2$ ground state and in the $6d_{3/2}^2 7s_{1/2}^2 7p_{1/2}^1$ excited state of Th$^-$ is $\approx1.5$ and $\approx1.1$ times bigger than in the $6d_{3/2}^2 7s_{1/2}^2$ ground state of the Th atom. The IC probabilities in the anion decreases despite the decay via the additional $6d_{3/2}$ or $7p_{1/2}$ electrons. This counterintuitive result is a consequence: a) of a decrease in the amplitudes of the $6d_{3/2}$ and $7s_{1/2}$ wave functions near the nucleus due to an increase in their diffuseness of upon the addition of extra electron, b) of mutual compensation in the IC probability due to a kinematic factor, which depends on the energy of the conversion electron in the continuum as $E_c^{-1/2}$, and the $E_c^{1/4}$ growth of the amplitudes of the electron wave functions.
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