Theoretical Investigation of Isotope Separation by Using Nuclear Excitation by Electron Transition

1. 轨道电子的激发能通常被发射的特征x射线或俄歇电子带走。然而，还有另一种通过激发核状态来释放能量的可能性。这是Morita很久以前在理论上指出的，并在^<189> o中进行了实验观察。这一过程被森田命名为电子跃迁核激发（简称NEET），原则上可以作为寻找极低的核激发态的方法，也可以作为不使用质量差的同位素分离方法，特别是在铀同位素等的情况下。我们研究了同位素表中可能产生NEET的原子核。通过假设原子核与电子之间的电磁相互作用为单光子交换相互作用，提出了一种新的NEET理论。在这个理论中，可以很容易地考虑到磁的多极跃迁。如果已知伽马衰变率的实验值，核矩阵元素的评估可以不使用特殊的核模型来完成。得到了磁偶极子和电四极子跃迁的NEET概率的显式公式。在^<189> o的情况下进行了数值分析。磁偶极子跃迁是NEET的主要组成部分。由于我们有一般公式，我们可以得到任何核素的NEET概率。

1. Excitation energy of the orbital electron is usually carried away by the emitted characteristic X-ray or the Auger electron. There is, however, another possibility of this energy release by exciting a nuclear state. This was pointed out by Morita theoretically long time ago, and experimentally observed in ^<189>Os. This process in named by Morita as the nuclear excitation by electron transition (in short, NEET), This can, in principle, be applied as a way of finding a very low-lying excited state of nucleus, as a method of isotope separation without using the mass difference, particularly in the case of uranium isotopes, etc.2. We have studied the atomic nuclei which are candidates to produce NEET, in isotope table.3. We have made a new theory for NEET, by assuming the one-photon exchange interaction for the electromagnetic interaction between the nucleus and electron. In this theory the magnetic multipole transitions can be taken into consideration very easily.4. Evaluation of the nuclear matrix elements can be done without using a special nuclear model, if the experimental values of the gamma-decay rates are known.5. Explicit formulas for NEET probability are obtained for the magnetic dipole and electric quadrupole transitions.6. Numerical analysis are made in the case of ^<189>Os. The magnetic dipole transition is the main component for NEET in this case.7. Since we have general formulas, we can obtain the NEET probability for any nuclides.