用于中国散裂中子源多功能反射谱仪的高气压多丝正比室探测器的研制

中国散裂中子源需要建设一台多功能反射谱仪中子探测器,满足在10年运行期间内,50%(@2A)以上的探测效率、好于2 mm的二维位置分辨、200 mm×200 mm的灵敏面积、3倍的n/γ分辨能力及良好的二维成像性能.基于此要求,探测器因此采用基于高气压~3He气体的多丝正比室,并以满足反射谱仪的探测效率、位置分辨、长期稳定工作和n/y分辨能力为目标进行探测器的设计.本文经过模拟和实验计算得出:以9 mm厚的铝合金入射窗、铝丝密封的高气压腔体和6 bar~3He+2.5 bar C_3H_8的工作气体的设计,可满足探测器对2 A中子10年运行期间内54%以上的探测效率要求;探测器对中子的位置分辨可达到1.4 mm左右;设计的气体净化系统,拥有2 L/min的气流速度可有效去除探测器内的负电性杂质气体,气体循环净化后可提高探测器约27%的气体增益,保证探测器长期稳定的运行;通过对~(252)Cf中子源的能谱测量和成像测量,得出探测器的n/γ分辨能力在5倍以上和均匀的成像结果.研制的探测器满足反射谱仪需求,并已在中国散裂中子源反射谱仪靶站就位联调.

Development of high-pressure multi-wire proportional chamber neutron detector for the China Spallation Neutron Source multipurpose reflectometer

As a multipurpose reflectometer device, the two-dimensional (2D) position resolution neutron detector with a 200 mm×200 mm effective area is developed for China Spallation Neutron Source (CSNS) in Dongguang, China. Due to the requirements for the specific parameters of the multipurpose reflectometer, it should be designed to have a more than 50% (@2 Å) detection efficiency, better than 2 mm position resolution and 3 times n/γ resolution ability during the whole operation period of 10 years. The high pressure multi-wire proportional chamber (MWPC) neutron detector filling ³He gas is used as a key detector. Some simulation results and the experimental results show that the optimized thickness of the neutron entrance window should be 9 mm with using the 7075 aluminum alloy, the high pressure chamber should be sealed by the aluminous ring and a gas mixture should be filled with 6 bar ³He+2.5 bar C₃H₈. The assembled detector can achieve a more than 54% (@2 Å) detection efficiency in the normal operation.
With the 100 μm wide collimator slit, the position resolution for X-rays is about 0.235 mm. Therefore, the position resolution for neutron is about 1.4 mm when 2.5 bar propane is used as the stopping gas for proton and triton. In the chamber, the water vapor, the oxygen and the organic impurity gases will reduce the gas gain, cause the detector electrodes to break down and the detector to speed up aging. To solve the outgassing effect of the detector components and keep the stable operation, the recycled device is designed to have the purification function for the working gases. It could purify the working gas at a flow rate of 2 L/min to remove the oxygen, the water vapor and the organic impurity gases. The detector gain increases about 27% with the purification function. Finally, the n/γ resolution and 2D imaging ability of the detector are tested with the ²⁵²Cf neutron source in Institute of High Energy Physics, Chinese Academy of Sciences, the peak ratio of neutron to gamma is obtained to be above 5 from the energy spectra and the detecor has good 2D imaging ability. The performance of the high-pressure MWPC neutron detector could meet the requirements for the multipurpose reflectometer, and the detector will be mounted in the CSNS in this year.