用直接中子法测量（n, 2n）反应截面的实验方法研究

Abstract

在中国原子能科学研究院HI-13 串列加速器上的非常规多探测器快中子飞行时间谱仪上，采用直接中子法测量了14.3 MeV 中子与169Tm作用的(n,2n) 反应截面。用蒙特卡罗方法模拟了次级中子的产生，以对实验数据进行中子注量率衰减、多次散射和有限几何修正，同时结合SUNF 方法得到的评价能谱，给出了(n,2n) 反应截面的实验测量结果。测量截面以中子弹性散射微分截面作为标准截面来归一，并用反冲质子望远镜测量n-p 反应的反冲质子，以监视中子注量率。用直接中子法测量得到的结果与评价数据进行了比较，讨论了采用这种方法测量(n,2n) 反应截面的可行性。 (n,2n) reaction cross section from 169Tm at 14.3 MeV was measured with the direct emittedneutron coincidence detecting method, using abnormal fast neutron TOF spectrometer on the HI-13 Tandem Accelerator at CIAE. Monte-Carlo method was used to simulate the generation of secondary neutron and correct the experimental data considering neutron flux attenuation, multiple scattering and finite geometry correction. Combining with evaluated spectra given by SUNF program, the experimental measurement results of the (n,2n) reaction cross sections were given. Cross sections of measurements were normalized by using neutron elastic scattering differential cross section as a standard section, and a recoil proton telescope was used to measure recoiling proton from the n-p reaction to monitor neutron flux rate. After comparing the experimental results with evaluated data, the feasibility of the direct emitted-neutron coincidence detecting method is discussed.