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

在京都大学(Kurri)研究堆研究所的46 MeV电子直线加速器上安装了一个铅慢化谱仪。测量了京都大学铅慢速谱仪(KULS)的特性：(1)中子慢化时间t(Mus)与能量E(Kev)的关系(双空穴E=190/t^2，铅空穴E=156/t^2)；(2)能量分辨率(双空穴和铅空穴-40%)；(3)用中子飞行时间法测量中子能谱。用MCNP程序计算得到的结果与实验结果基本一致。利用背靠背双裂变室测量了Am-241、Am-243和Am-242M相对于U-235的裂变截面，范围从-0.1 eV到-10keV。对于AM-214，DABBS和ENDF/B-VI数据与目前的测量结果符合得很好。JEND L-3.2的数据在10-200 eV之间小2倍，Am-243的ENDF/B-VI数据在15-60 eV之间较低，JENDL-3.2的数据一般在100 eV以上。研究发现，Am-242m(n，f)反应的初步结果与ENDF/B-VI和JENDL-3.2数据接近。在标准的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核素俘获截面的测量，用KULS对Np-237样品(-2 mg)进行了实验研究。由于背景计数与前景计数相当，用Ar气体正比计数器很难探测到样品的俘获事件。

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.