Study on Measurements of Nuclear Data for Transmutation of Actinide Elements using Lead Slowing-down Spectrometer

在日本京都大学反应堆研究所（KURRI）的46 MeV电子直线加速器上安装了一个铅减速光谱仪。利用中子TOF法测定了京都大学铅慢化光谱仪（KULS）中子慢化时间t （mus）与能量E (keV) （Bi空穴E=190/t^2， Pb空穴E=156/t^2）、能量分辨率（Bi和Pb空穴E= -40%）和中子能谱的关系。MCNP程序计算结果与实验结果基本一致。利用背对背式双裂变室，KULS在-0.1 eV到-10 keV范围内对Am-241、Am-243和Am-242m相对于U-235的裂变截面进行了测量。对于Am-214， Dabbs和ENDF/B-VI数据与目前的测量结果吻合良好。JEND L-3.2数据在10到200 eV之间小了2倍。Am-243的ENDF/B-VI数据在15 ~ 60 eV之间较低，JENDL-3.2的ENDF/B-VI数据在100 eV以上总体较低。发现Am-242m （n, f）反应的初步结果与ENDF/B-VI和JENDL-3.2数据接近。在标准麦克斯韦分布谱场中测量了Am-241和Am-243的热中子截面。最后，针对MA核素捕获截面的测量，用KULS对n237样品（- 2mg）进行了实验研究。由于背景计数与前景计数相当，样品中的捕获事件几乎无法用Ar-gas比例计数器检测到。

A lead slowing-down spectrometer was installed coupled to the 46 MeV electron linac at Research Reactor Institute, Kyoto University (KURRI). Characteristics of the Kyoto University Lead Slowing-down Spectrometer (KULS) were measured for (1) the relation between neutron slowing-down time t (mus) and energy E (keV) (E=190/t^2 in Bi hole and E=156/t^2 in Pb hole), (2) the energy resolution (-40% in Bi and Pb holes), and (3) the neutron energy spectrum by the neutron TOF method. The results obtained by the MCNP code were in general agreement with these experimental ones.The KULS has been applied to the fission cross section measurements of Am-241, Am-243 and Am-242m relative to that of U-235 from -0.1 eV to -10 keV,making use of the back-to-back type double fission chambers. For Am-214, Dabbs and ENDF/B-VI data are in good agreement with the present measurement. The JEND L-3.2 data are smaller by a factor of 2 between 10 and 200 eV.The ENDF/B-VI data for Am-243 are lower between 15 and 60 eV,and the JENDL-3.2 are lower in general above 100 eV.It has been found that the preliminary result for the Am-242m (n, f) reaction is close to the ENDF/B-VI and the JENDL-3.2 data. Thermal neutron cross sections for Am-241 and Am-243 have also been measured in a standard Maxwellian distribution spectrum field.Finally, aiming at the measurement of capture cross section for MA nuclides, the experimental investigation for Np-237 sample (-2 mg) has been performed with the KULS.Due to the comparable background counts to the foreground ones, the capture events from the sample have scarecely been detected with an Ar-gas proportional counter.