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

1.轨道电子的激发能量通常被发射的特征X射线或俄歇电子带走，然而，还有另一种可能性，即通过激发核态释放这种能量。这一点早在很久以前就被森田从理论上指出了，并在1980年被实验上观察到<189>。森田将这一过程命名为电子跃迁核激发（简称NEET）。原则上，这可以作为一种寻找原子核的低激发态的方法，作为一种不利用质量差的同位素分离方法，特别是在铀同位素的情况下，等等。我们在同位素表中研究了产生NEET的候选原子核.我们建立了一个新的NEET理论，把核与电子之间的电磁相互作用假定为单光子交换作用，在这个理论中，磁多极跃迁可以很容易地考虑进去.如果γ衰变率的实验值是已知的，那么核基质元素的评估可以在不使用特殊核模型的情况下进行。得到了磁偶极跃迁和电四极跃迁的NEET几率的显式表达式.对^Os的情况进行了数值分析<189>，磁偶极跃迁是NEET的主要成分.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.