Measurement of Neutron Capture Cross Sections of Radio-active Fission Product Nuclides

为获得放射性废物核嬗变的基础数据，测量了裂变产物核素的中子俘获截面。由于放射性靶的处理困难，放射性核素的俘获截面数据较少，本文通过比较靶核素和中子俘获过程产生的核素的活度，得到了俘获截面数据。1991年，我们测量了^<137>Cs（n，γ）^<138>Cs反应截面。由于~（12）Cs和~（13）Cs活度的测量<137><138>是同时进行的，因此自动消除了电子系统的计数损失和化学净化过程的分离产率等各种误差源。测得反应截面为0.250 × 0.013 barn，比Stupegia报道的结果大2.3倍，1992年用同样的方法测量了^<90>Sr（n，γ）^<91>Sr反应截面。得到的截面值为15.3 * 1.3mb。还测量了使用μ <137>Cs（n，γ）μ <138>Cs的积分的共振值，并且获得的值为0.36 * 0.07 B。结果表明，共振积分的影响可以忽略不计，这一研究结果提供了新的、可靠的^ Cs和^Sr的中子俘获截面数据<137><90>，其结果将发表在《核科学与技术》上。

Neutron capture cross sections of fission product nuclides were measured to obtain basic data for nuclear transmutation of radio-active waste. There are few data of capture cross sctions of radio-active nuclides since the handling of the radio-active target is difficult.In this study, cross sections were obtained by comparing the activities of a target nuclide and a nuclide produced by the neutron capture process. Activities of both nuclides were measured simultaneously using a large Ge detector.In 1991, the cross section of ^<137>Cs(n,gamma)^<138>Cs reaction was measured. Since the measurement of activities of ^<137>Cs and ^<138>Cs were made simultaneously, various sources of errors such as the counting loss of electronic system and the separation yield of chemical purification process were automatically canceled. The value of cross section obtained was 0.250 * 0.013 barn, and this value is 2.3 times larger than the value reported by Stupegia.In 1992, measurement of the cross section of ^<90>Sr(n, gamma)^<91>Sr reaction was performed by using the same method. The value of cross section obtained was 15.3 * 1.3 mb. The value of resonance using the integral of the ^<137>Cs(n, gamma)^<138>Cs was also measured and the value obtained was 0.36 * 0.07 b. It was found that the effect of resonance integral was negligible.This study presents new and reliable data of neutron capture cross section of ^<137>Cs and ^<90>Sr. The results will be published in Nuclear Science and Technology.