基于中子位置灵敏探测器对点源的三维定位方法研究

Three-dimensional point-source localization method based on position-sensitive neutron detectors

使用中子法对密封容器内的放射源进行定位具有重要的现实意义。本研究使用4根矩形分布的中子位置灵敏探测器对探测空间内AmLi源进行定位,首先使用蒙特卡罗方法设计了探测器的慢化屏蔽体;然后设计了延迟电路加到探测器的一端,根据探测器两端探测到中子信号的时间差来确定源y轴(探测器轴向)的位置坐标,并对每个探测器的轴向位置函数进行了刻度;利用探测器围绕密封容器搭建测量空间,使用相邻探测器探测到中子计数率的比值来确定x轴和z轴(另两个方向)的位置坐标并进行了函数刻度。测量时,首先选择计数率最大的探测器来确定源的轴向坐标,再根据与此探测器相邻两根探测器计数率的比值来确定源的另两个方向的坐标,实现了对源的定位。使用该方法测量了点源在探测器空间内的5个不同位置,每个坐标轴上的定位偏差均在1.5 cm之内,并对造成偏差的原因进行了分析。该方法验证了使用中子位置灵敏探测器对放射源进行定位的可行性,并为进一步测量核设施工艺设备内核材料的位置打下了良好的基础。

[Background]The use of neutron-based methods to locate radioactive sources within sealed containers holds great practical significance.[Purpose]This study aims to locate an AmLi source within the detection space of four position-sensitive neutron detectors.[Methods]First of all,the Monte Carlo method was applied to designing the moderating shield of the detector.Then,a delay circuit was added to one end of the detector hence the position coordinate of the source y-axis(detector axis)was determined according to the time difference between the two ends of the detector to detect the source neutron signal,and the axial position function of each detector was calibrated.Finally,the detector was used to build a measurement space around sealed container,and the position coordinates of the x-axis and z-axis(the other two directions)were determined by the ratio of the neutron count rate of the two adjacent detectors,so was the function calibration.During the measurement of neutron point-source 3D coordinates,the detector with the largest count rate was first selected to determine the axial coordinates of the source,and then the coordinates of the other two directions of the source were determined according to the ratio of the count rate of the two adjacent detectors to the detector,so as to realize the location of the source.[Results]Measurement results of five different positions of the point source in the detection space show that the positioning deviation on each coordinate axis is within 1.5 cm,and the relative standard deviation of neutrons measured in this detection space is within 1%.[Conclusions]This methodology effectively demonstrated the feasibility of employing neutron positionsensitive detectors to precisely locate radioactive sources,establishing a strong foundation for future endeavors aimed at accurately determining the positions of nuclear materials within processing equipment in nuclear facilities.