低强度脉冲辐射场的电流型计数测量方法研究

Pulsed radiation field measurement is an important subject in the studies of particle physics and nuclear physics. The traditional measurement methods in which the detectors are working in counting mode or current mode all have limitations in this kind of measurement. Current-Mode-Counting method, which employs the techniques as high speed ADC and digital signal processing, is a new method of radiation field measurement proposed by us. In this method, the current output of a radiation detector will be directly quantified and then processed with the techniques of digital signal processing, and the information of the radiation field can be acquired from the processing results. Since it has no stage of pulse shaping by analogue circuit compared to the traditional method, the information carried by the signal will be largely preserved. With the study of the international digital design techniques in radiation measurement as well as the techniques' development trend , we propose to develop a measurement system with Current-Mode-Counting method applied to low intensity pulsed radiation field measurement, while study the characteristics of the radiation detectors in the system and the techniques that will be employed in the study as follows: high speed analogue-to-digital conversion, high speed large data storage and data analysis of radiation field with DSP. The system is expected to measure the pulsed radiation field with the intensity between 1E6cps and 1E8cps which cannot be measured efficiently by traditional methods, and the particles' information of type, energy and time can be measured. The method also has the potential advantage as the reusability of the original data.

脉冲辐射场测量是粒子物理与核物理研究中的重要研究内容。传统的电流型测量和计数型测量应用在该领域时均有局限。本课题组提出的电流型计数测量方法是利用高速模拟数字转换和数字信号处理等技术建立的新的辐射场测量模式，其原理是将辐射探测器输出的电流信号直接量化并分析，从而实现对辐射场的诊断。相对于传统的计数型测量，该方法不对探测器输出的信号进行整形，因此有望保留该信号所包含的完整信息。通过研究国际辐射测量领域中数字设计技术及发展趋势，课题组针对脉冲辐射场测量设计电流型计数测试系统，分析探测器性能，研究高速模拟数字转换、高速大容量存储和基于DSP的辐射场测量数据分析等技术，期望实现对传统测量方式测量效果不理想的、事件率在1E6cps-1E8cps的脉冲式混合辐射场的粒子种类、能量和时间信息的综合测量。同时该方法还具有测量原始数据可重复利用的优点。

研究了电流型计数测量方法的原理，分析测量系统的构成并讨论了系统中探测器和电子学系统的性能特点与可采用的技术路径。讨论了数据采集系统的工作方式，并对工作方式与系统计数率的关系进行了理论分析。分析了电流型计数测量方法的统计性以及该方法在脉冲幅射场测量中的适用性。对测量系统组建中数据采集系统性能的估算方法进行了理论分析；讨论了能谱与时间谱的统计算法。.开展电流型前置放大和高速数据采集两项关键电子学技术研究。通过采用集成运算放大器和RF放大器，实现了三种结构的放大带电路，适用于上升时间为ns量级、幅度在亚mV量级的微弱快脉冲信号的线性放大。研制了适用于电流型计数测量的高速数据采集电路，达到1 GS/s采样率、12-bit垂直分辨率、250 MHz带宽。.组建了实验样机平台，利用无机闪烁体、液体闪烁体和Si-PIN等探测器，开展了γ射线、中子、α粒子和脉冲质子束测量实验，验证了测量原理。研究了数据处理方法，实现了利用数字信号处理的方法获取粒子测量信息。实验中实现了粒子能量和入射时刻的联合测量，验证了粒子种类信息获取功能，获得了2.2×106 s-1的计数率。采用Si-PIN半导体探测器时理论计数率达到107 s-1。.研究结果表明该方法可实现对传统测量方式测量效果不理想的、探测器输出事件率在106~108 s-1的脉冲辐射场的粒子种类、能量和时间信息的综合测量。