基于外延碳化硅材料的裂变法强流中子探测技术研究

Semiconductor detector used in fission neutron detection in complex radiation environment needs high n/γ discrimination, high linear current, proper sensitivity, fast response time, and so on. Conventional silicon p-i-n diode detector cannot get high n/γ discrimination due to its thick sensitive volume, much larger than the depth of fission fragments, thus the development of neutron detection technology in intense pulsed fission was badly restricted. Homo-epitaxial growth technology, well developed in recent years, makes it possible to fabricate silicon carbide (SiC) detector with lightly doped material and with thickness in the range of to 10 microns to 100 microns. Interfering signal of gamma ray and scattered neutron could be significantly reduced with thin sensitive volume. The SiC detector, with good n/γ discrimination and excellent charge collection efficiency of nearly 100%, can enhance the response character of pulsed neutron detection system remarkably. However, sensitive area of SiC detector is not big enough; important basic problems in intense pulsed detection, not only linear current, but also n/γ discrimination, and such problems as ballistic deficit, have not been well studied. It is urgent to use homo-epitaxial silicon carbide material for intense pulsed fission neutron detection technology. In this project, large area silicon carbide detector is soon fabricated, key response characteristic is about to be studied, the pulsed neutron detection system based on silicon carbide detector will be established and calibrated, and its application in neutron detection is going to be explored. This study will help developing of semiconductor radiation detector and detection of intense pulsed neutrons.

强流脉冲中子伽马混合场的中子诊断，要求探测器具有高n/γ分辨能力、大线性电流、合适灵敏度和快时间响应等性能，而传统的大面积硅PIN探测器（灵敏区较厚）存在n/γ分辨不理想、抗辐照能力差、不适用于高温工作环境等问题，已不能满足中子探测的需求。新兴的碳化硅（SiC）同质外延技术解决了材料的低掺杂生长和厚度精细调控的难题，故可根据中子引发的二次粒子和裂变碎片的探测需求制作薄灵敏区（十几至几十微米）的SiC探测器，此类器件的抗干扰能力强、电荷收集效率高、耐辐射、耐高温，有望显著提升脉冲中子诊断系统性能；但是存在灵敏面积太小，关键性能指标（最大线性电流、n/γ分辨力、裂变碎片的能量亏损等）不清楚等问题。本项目拟攻克大面积SiC核探测器制作难题，发展新的强流脉冲中子探测系统和绝对刻度方法，开展关键性能和应用基础研究，探索在中子探测中的应用，对半导体探测器和强流脉冲中子探测技术的发展具有重要的意义。

脉冲混合辐射场中子参数的高精度诊断对研究核反应过程及机理非常重要，必须建立具有数十倍超高中子/散射中子和中子/伽马分辨能力、对源裂变中子能谱具有平坦能量响应、快时间响应的裂变中子探测技术。基于核裂变过程的裂变法是实现平坦能量响应的理想选择，但受制于传统硅探测器灵敏区过厚，裂变法的信噪比一直不理想。本课题首次成功探索研究了外延式薄型SiC探测器件作为裂变法中子探测器件的探测技术原理、方法和技术途径，研制成功灵敏区厚度约20~30m、电荷收集效率近100%、线性电流3A以上、灵敏区面积4cm2、耐辐照能力远超Si-PIN探测器的高性能SiC辐射探测器件，基此成功研制了新型脉冲裂变中子探测系统，实现了探测技术从第一代硅探测器到SiC宽禁带探测技术的跨越。.课题研究突破了大面积高性能SiC探测器关键制作技术，成功研制了裂变法探测系统所需的新型探测器，研究并获得了SiC探测器的辐射响应性能；发展了高信噪比的裂变中子探测技术；开展了SiC探测器的应用研究，研发了基于SiC结型探测器的中子束流实时监测系统，实现了CPNG-600kV高压倍加器中子产额的实时准确监测。.综上所述，本课题在脉冲中子探测技术需求的牵引下，结合新型探测器研制和辐射探测技术研究，通过半导体物理新发展与辐射探测技术的交叉结合，研制了高性能SiC探测器，发展了新的脉冲中子探测方法，研发了裂变法中子探测系统，实现脉冲中子探测从传统硅基器件向宽禁带半导体探测器的跨越。成功探索了SiC 核探测器在加速器束流监测中的应用，为相关国内辐射装置和中子探测提供了新的选择。