中子三轴谱仪部件模拟与优化计算

Simulation of triple-axis spectrometer and parameter optimization

根据三轴谱仪的安装位置及后续结构,利用蒙特卡罗方法模拟计算了中子三轴谱仪样品处的中子谱,获得了中子均匀性、注量率等参数。模拟结果表明:采用双聚焦单色器的中子注量率是采用平板单色器中子注量率的1.54倍,但中子分布均匀性变差,垂直发散度增大到约4°;聚焦单色器的聚焦长度对中子均匀性无影响,但聚焦长度越长其垂直发散度越小;入射单色中子波长λ<0.4nm时,用热解石墨做过滤器比较合适,而当λ≥0.4nm时,用铍做过滤器更合适一些。

According to layout of a triple-axis spectrometer （TAS）, neutron beam parameters at the sample position, such as the homogeneity, divergence and flux, were calculated by Monte-Carlo simulation. The results show that using a double-focusing monochromator, the beam flux is 1.54 times larger, but the neutron distribution is worse, than using a flat monochromator, while the vertical maximum divergence increases to 4°. Vertical divergence of the neutrons decreases with increasing focusing lengths, while the beam homogeneity does not change obviously. A pyrolytic graphite （PG） filter is suitable for neutrons in wavelengths of less than 0.4 nm, while a Be filter is better than PG filter for neutrons in wavelengths of longer than 0.4 nm.