用于CSNS反角白光中子源的双屏栅电离室设计及性能研究

为测量中国散裂中子源（China Spallation Neutron Source, CSNS）反角白光中子源150 keV以下能区飞行时间法中子能谱，研制基于¹⁰B(n, α)⁷Li和⁶Li(n, t)α核反应的双屏栅电离室，采用薄窗和薄底衬的结构设计。通过Garfield++、SRIM和Simcenter Magnet Electric程序对屏栅电离室的工作气体、极间距和电场分布等工作参数进行模拟设计，并采用α源及CF₄、P10、90%Ar-10%CO₂三种气体对电离室进行性能参数测试。结果表明，选定电子漂移速度快、扩散系数小，以及阻止本领大的CF4作为CSNS/Back-n束上测试工作气体，阴极-栅极和栅极-阳极间距分别为20 mm和5 mm。屏栅电离室收集区74 mm范围内是电场均匀区，场强的相对偏差≤0.03%；性能测试结果表明，工作气体为CF₄时，电离室对²³⁹Pu/²⁴¹Am/²⁴⁴Cm混合α面源具有很好的能量分辨，最佳能量分辨率为2.4%@5.48 MeV。对比平板型电离室和硅微条探测器的测量结果，验证了本工作研制的屏栅型电离室的能量分辨优势。

Design and Preliminary Property Research of Double-Grid Ionization Chamber for CSNS Back-n White Neutron Source

A double-grid ionization chamber(GIC) based on the 10B(n,α)7Li and 6Li(n,α)T nuclear reaction has been developed for neutron energy spectrum measurement in the energy region below 150 keV of CSNS/Back-n by time of flight method. According to the strong adjoint gamma-flash features, the structure design of thin window and thin bottom lining is adopted. In view of the characteristics of strong gamma-flash neutron beam, the structure design of thin bottom lining is adopted. Garfield++, SRIM and Simcenter Magnet Electric simulation programs are used to simulate the working parameters such as working gas, electrode spacing and electric field distribution of the GIC. CF₄, which has fast electron drift speed and small diffusion coefficient and great organizing ability, is selected as the working gas for the CSNS/Back-n beam test with cathode-grid and grid-anode spacing of 20 mm and 5 mm, respectively. The collecting area within 74 mm can be considered as the uniform electric field area, and the relative deviation of the field strength is not more than 0.03%. The performance of the GIC was tested by α source. The GIC has good energy resolution for ²³⁹Pu/²⁴¹Am/²⁴⁴Cm mixed α surface source with CF4. And the best energy resolution is 2.4%@5.48 MeV. Compared with the measured results of the parallel-plate chamber and the silicon microstrip detector, the advantages of energy resolution of the GIC developed in this work are verified.