Gadolinium Isotope Separation by Polarized Lasers

钆具有较高的中子吸收截面，是核电站中重要的可燃毒物。Gd有7个同位素组成。特别是^<157>Gd具有明显的大截面。浓缩^<157>Gd可以提高核燃料的燃烧速率。由于Gd的同位素位移非常小，所以很难用窄带激光激发一种同位素。而基于偏振选择规则的偏振激光分离方法则适用于该元件。在这种方法中，作为金属蒸发源的电子枪中含有的磁体产生的外磁场可能会降低同位素的选择性。在设计大型分离装置时，研究外磁场作用于激光-原子相互作用区域时原子的激发行为是非常重要的。本研究得到的结果总结如下：1。在小尺度实验中，利用三束线偏振激光器实现了奇同位素（^<155>Gd, ^<157>Gd）的高选择性电离。当外加磁场作用于激光-原子相互作用区时，观察到选择性损失。通过测量同位素选择性与磁场强度、激光极化与磁场夹角的关系，发现实验结果与我们编写的计算程序的结果吻合得很好。实验和数值分析表明，当激光脉冲宽度为5ns时，20mT的磁场完全降低了选择性。这表明，当50ns激光脉冲辐照时，在2mT的磁场下，完全不可能有选择性。

Gadolinium (Gd) is an important element as a burnable poison in nuclear power plant due to its high neutron absorption cross section. Gd has seven isotopic components. Especially, ^<157>Gd has a distinct large cross section. The burn rate of the nuclear fuel can be enhanced by enriched ^<157>Gd. It is difficult to excite one isotope using a narrow band laser because Gd has very small isotope shifts. Separation method, however, using polarized lasers based on polarization selection rules is suitable for this element. In this method the isotopic selectivity could possibly degraded by an external magnetic field generated by a magnet contained in the electron gun as a metal evaporation source. For designing a large-scale separation facility it is important to investigate the atomic excitation behavior when an external magnetic field is applied in the laser-atom interaction region.Obtained results in this study are summarized below.1. Highly selective ionization of odd isotopes (^<155>Gd, ^<157>Gd) was achieved in the small-scale experiment using three linearly polarized lasers.2. Selectivity loss was observed when an external magnetic field was applied in the laser-atom interaction region.3. From the measurement of isotope selectivity as a function of a magnetic field strength, the angle between the laser polarization and the magnetic field, it was found that the experimental results well agreed with the results of the calculation code we developed.4. Both the experiment and the numerical analysis showed that a magnetic field of 20mT could completely degrade the selectivity when the laser pulse widths were 5ns. This suggests that the selectivity could not be expected at all for a magnetic field of 2mT when the 50ns laser pulses are irradiated.