基于电荷差位置读出法的新型管形中子探测器研究

Neutron scattering techniques are playing an important role in the study of material structure and dynamic properties, which are widely used in various subjects. The neutron scattering spectrometers for China advanced research reactor (CARR), Chinese spallation neutron source (CSNS) and other large neutron science device require the neutron detector with high detection efficiency and high position sensitive. 3He neutron detector is an ideal one for many neutron spectrometers. However, due to the shortage of 3He gas and the rapidly increasing price, seeking new neutron detectors to replace 3He neutron detector are urgent. The advantages of scintillator detector, including high position resolution, low n/γ rejection ratio, real-time detecting and so on, make it widely used in many neutron instruments. The traditional scintillator neutron detector which uses flat structure has several disadvantages, such as low neutron detection efficiency, complex readout method of optic fiber signal, large electronic structure, et al.. The traditional scintillator neutron detector is difficult to completely replace the 3He-gas-based detector..A position-sensitive cylindrical scintillator-based neutron detector is proposed as an alternative to the 3He-gas-based detector. The detector has a neutron-detecting element constructed from rolled 6LiF/ZnS(Ag) scintillator screens that sandwich wavelength-shifting(WLS) fibre coils. These rolled elements are enclosed in an aluminium tube in a row to form an one-dimensional position-sensitive neutron detector. This scintillator/WLS fibre structure significantly decreases the required number of light-collection fibres and the read-out detector electronics compared to the one using an array of WLS fibres. Moreover, the two rolled scintillators ensure a high rate of neutron absorption. The scintillator screen in the detector element is essentially four fold thicker for incident neutrons relative to the one using a single scintillator screen. A novel optical signal readout method based on the charge difference is applied in this project. By comparing the difference of the photon number from each end of the fiber, the one-dimensional position of the incident neutron is calculated. .The compact construction of the detector will be designed to fulfill the high detect efficiency and high spatial resolution. Key technologies will be grasped through the R&D of this detector, which will be used in the volume production in future. The cylindrical shape of the new detector is similar to the usual 25-mm-diameter 3He tube, making this an alternative detector with the potential to be installed in the neutron scattering instruments.

中子是研究物质结构的理想探针。随着中国先进研究堆(CARR),中国散裂中子源(CSNS)等大型中子科学装置的建设, 大量中子散射谱仪要求具有高探测效率、高位置精度等的高性能中子探测器。受限于3He气体资源的日益匮乏，国际上寻找替代3He的新型中子探测器一直是研究热点。本项目提出一种基于电荷差位置读出方法的新型管形闪烁体中子探测器，其利用6LiF/ZnS(Ag)闪烁体和波移光纤的筒形夹心结构，实现高探测效率，高位置分辨率等性能。该结构下的探测器，通过对比缠绕式光纤两端传输的光信号差，计算出闪烁光被光纤吸收的位置，从而得到入射中子的位置信息。通过该探测器的研制，可以掌握闪烁屏和波移光纤的卷曲定位工艺，发展基于电荷差位置读出方法的电子学，为该探测器替代传统3He管中子探测器奠定基础。

随着中国先进研究堆(CARR)和中国散裂中子源(CSNS)等大型中子科学装置的建 成,大量中子散射谱仪要求其中子探测器系统能够实现大空间大立体角覆盖、高集成度、 高性能的实时快速探测。传统的3He型探测器由于价格高昂，研制新型大面积阵列型中子 探测器迫在眉睫。利用中子敏感闪烁材料和波移光纤结构的位敏型中子探测器是目前国际 上用于替代3He型中子探测器的研究热点。本项目研究的基于电荷差位置读出法的管形中子探测器，结构设计上利用卷曲后的6LiF/ZnS(Ag)闪烁体和波移光纤形成紧凑的筒形夹心结构，最终实现较高的热中子探测效率和好于4mm的位置精度。该种管形中子探测器在性能指标上，具有和传统3He管相比拟的优点：探测效率高，结构紧凑，可大面积拼接。同时还具有位置分辨高，造价低廉等优点，可以成为很好的3He替代型中子探测器。