Measurement of Continuous Energy Neutron Incident Neutron Production Double Differential Cross Sections

在美国洛斯阿拉莫斯中子科学中心的WNR装置上，对能量高达400 MeV的Al、Fe、In和Pb样品进行了连续能中子-入射中子-产生双微分截面的测量。由于飞行时间法无法确定入射中子入射到样品的时间，因此难以获得发射中子能量。入射和发射的中子能量分别由飞行时间法和探测器中的沉积能量展开谱数据获得。反冲质子法用于100 MeV以上的高能发射中子探测。该探测器采用phoswich结构，通过脉冲形状鉴别将全部能量沉积事件与部分能量沉积事件分离。这种方法由于有效探测效率低，需要大量的射束时间。厚靶中子产额进行了测量，以确认反冲质子方法的有效性试验。利用液体有机探测器测量了100 MeV以下的低能发射中子，在WNR装置上用低强度连续能中子测量了探测器的响应函数，并与SCINFUL-QMD程序的结果进行了比较。将移动源模型的发射中子能谱作为期望中子能谱。由于探测系统无法从所有存储的事件数据中区分出弹性散射事件，因此在运动源模型中加入了弹性散射分量。发射中子能谱是通过对中子源的光输出数据展开得到的。结果发现，LA 150评估核数据库低估了几十MeV以上入射能量的后向实验数据。

Measurement of continuous-energy neutron-incident neutron-production double-differential cross sections were carried out for Al, Fe, In and Pb sample up to 400 MeV at the WNR facility of Los Alamos Neutron Science Center. It was difficult to adopt the time-of-flight method to obtain an emitted-neutron energy because it was unable to identify the time that an incident neutron was induced to a sample. The incident- and the emitted-neutron energy was obtained by the time-of-flight method and unfolding spectrum data of the deposited energy into a detector, respectively. The recoil proton method was adopted for higher-energy emitted-neutron detection above 100 MeV. The detector has phoswich configuration to separate full energy deposition events from partial energy deposition ones by pulse shape discrimination. This method needed much beam time because of low effective detection efficiency. Thick target neutron yields were measured to confirm availability of the recoil proton method on trial. Liquid organic scintillators were utilized for lower-energy emitted-neutron measurement below 100 MeV, Response functions of the detector were measured using low-intensity continuous-energy neutron at the WNR facility and compared with the results by the SCINFUL-QMD code. The emitted-neutron energy spectrum by the moving source model was assumed as desired neutron spectrum. Elastic scattering component was added to the moving source model because the detection system was unable to distinguish the elastic scattering events from all stored event data. The emitted-neutron spectra were obtained by unfolding the light output data from scintillators. It was found that the LA150 evaluated nuclear data library underestimated the backward experimental data for the incident energy above several tens MeV.