中子反射谱仪前端导管优化

Optimization of pre-guide of neutron reflectometer

基于两种中子反射谱仪设计(A:前端为8.0 m垂直聚焦导管,入口200 mm,出口40 mm;B:前端为1.6+3.4 m水平偏转垂直聚焦导管,入口100 mm,出口50 mm),对其前端偏转/聚焦导管进行了中子束模拟,结果表明:1)在特征波长为0.4 nm的冷中子导管末端,没有必要再次偏转束流以减低本底;2)与建议方案相比,概念设计中的注量下降了52.8%,而水平方向发散度增大了24.1%,垂直方向发散度减小60.7%;3)聚焦导管长度应不低于6.0 m,导管聚焦超镜m值在2.0?2.5最佳,两侧超镜m值对束流几乎无影响,使用中子束高度应不低于150 mm可达到较好的注量率和发散度。

In this work, Monte Carlo simulations were done for optimization of pre-guide of neutron reflectometer （NR） in two proposals： A, pre-guide of 8.0 m in length, vertical focusing guide of 200-mm entrance and 40-mm exit height; B, pre-guide of （1.6 ＋ 3.4） m long, vertical focusing and horizontal deflecting guide of 100-mm entrance and 50-mm exit height. The following results were found： 1） it is not necessary to deflect neutron beam for NR at the exit of cold neutron guide, 2） compared proposal A with B, the flux at pre-guide exit decreases 52.8% and divergence increases 24.1% in horizontal direction and decreases 60.7% in vertical plane, and 3） a optimized pre-guide should not be shorter than 6.0 m, focusing super-mirror factor m in the range between 2.0 and 2.5, and its entrance height no less than 150 mm.