用于CSNS反角白光中子能谱及注量率测量的快裂变室

即将建成的中国散裂中子源(China Spallation Neutron Source,CSNS)反角白光中子束线可为核数据测量提供高注量率的脉冲白光中子束流,填补我国核数据测量用白光中子源的空白,提高我国核数据测量水平,满足核能、核技术及基础核物理研究对核数据的需求。该束线建成后,其中子能谱及注量率的精确测量将是开展其它物理实验的基础,快裂变电离室因其独特优点被选为中子能谱和注量率测量探测器。通过实验研究了快裂变电离室的粒子分辨性能、时间分辨性能;确定阴、阳极的合理间距为10 mm,据此测得电离室的时间分辨约15 ns;利用235U样品量计算的探测效率与利用伴随粒子法给出的探测效率在不确定度范围内符合,因此可以标定快裂变室的探测效率。通过这些工作,完成了满足反角白光中子束能谱及注量率测量需求的快裂变室的物理设计。

Physical design of fast fission chamber for neutron spectrum and flux measurement at the CSNS backstreaming white neutron source

Background:The backstreaming white neutron source (Back-n) of China spallation neutron source (CSNS) will provide pulsed white neutron beam with a high fluence rate for nuclear data measurement. The accurate measurement of the neutron spectrum and fluence rate after the Back-n's completion will be the basis of the following physical experiments.Purpose: This study aims to design a fast fission chamber for the CSNS Back-n flux measuring and monitoring system. Methods: The detector performance including time resolution, particle distinction and detection efficiency was studied by experiments. Based on the study, the parameters of the fission chamber were determined, and its detection efficiency calculated by the235U sample quantity was compared with that measured by concomitant particle method.Results: Considering the particle distinction, the distance between the anode and the target of the fission chamber was determined as 10 mm, the time resolution of the fission chamber was measured to be about 15 ns. The deviation of calculated detection efficiency from the measurement was in the range of 5%. Conclusion: According to the detection efficiency and the demand of the neutron flux monitoring, the quantity of the uranium for the fast fission chamber can be determined. With appropriate parameters, the fast fission chamber can be used in CSNS Back-n flux measuring and monitoring.