高取向热解石墨单色中子束级次分析  

Analysis of Higher-order Neutrons Monochromated by Highly Oriented Pyrolytic Graphite

作　　者：王子军[1] 李天富[1] 余周香[1] 刘荣灯[1] 李玉庆[1] 贺林峰[1] 刘蕴韬[1] 孙凯[1] WANG Zijun;LI Tianfu;YU Zhouxiang;LIU Rongdeng;LI Yuqing;HE Linfeng;LIU Yuntao;SUN Kai(China Institute of Atomic Energy,Beijing 102413,China)

机构地区：[1]中国原子能科学研究院,北京102413

出　　处：《核科学与工程》2021年第5期885-890,共6页Nuclear Science and Engineering

基　　金：国家重点研发计划2017YFA0403701;国家自然科学基金12075320。

摘　　要：高取向热解石墨HOPG具有优异的中子反射性能,在中子散射技术中广泛用作中子单色器,而使用它获得单色中子时可能会伴随严重的次级污染。本文分别使用晶体衍射方法和飞行时间方法,分离出HOPG单色后的初级、次级和三级衍射束,并测量得到了各级次中子的相对强度。测量结果显示,在没有冷中子源时,中国先进研究堆反射谱仪样品位置中子束次级含量与初级相当,给单色束带来严重污染。室温下铍过滤器可以过滤掉所有次级中子,但初级中子强度也明显衰减。蒙特卡罗中子光路模拟和分析给出次级中子含量高是由于室温条件下导管出口中子能谱过硬,而在使用冷中子源后,次级中子含量可显著降低。Highly Oriented Pyrolytic graphite(HOPG)has become indispensable in neutron spectroscopy because of its high performance in terms of neutron reflectivity.But serious higher-orders contamination could accompany the monochromated neutron beam simultaneously.Both crystal diffraction and time of flight were exploited to separate the 2 nd and 3 rd orders from the 1 st order neutrons diffracted by a HOPG at the sample position of neutron reflectometer at China Advanced Research Reactor,obtaining their relative intensity.The measurements indicate that the 2 nd and 3 rd orders are comparable to the 1 st order,which demonstrates serious contamination to the monochromatic beam.A beryllium filter used at room temperature put into the neutron beam completely removed the higher-order components.Further analysis with MonteCalo simulation indicates that the main reason of nontrivial higher-order neutrons is due to thermal neutron spectrum at the guide out.Simulation results also demonstrated that higher-orders composition would be significantly decreased with the use of cold neutron source.

关 键 词：中国先进研究堆 高取向热解石墨 中子单色器 蒙特卡罗 

分 类 号：TL48[核科学技术—核技术及应用]