Zeng Guoqiang, Tan Chengjun, Li Qiang, Ge Liangquan, Liu Xiyao, Luo Qun
Chengdu University of Technology, Sichuan 610059, China.
Chengdu University of Technology, Sichuan 610059, China.
Appl Radiat Isot. 2015 Mar;97:63-69. doi: 10.1016/j.apradiso.2014.12.009. Epub 2014 Dec 18.
The time constant of the output signal of the front-end readout circuit of a traditional gamma-ray spectrometer with a NaI(Tl)+PMT structure is affected by temperature, measurement environment and the signal transmission cable, so it is difficult to get a good resolution spectrum, especially at higher counting rates. In this paper, a reset charge sensitive amplifier (RCSA) is designed for the gamma-ray spectrometer with a NaI(Tl)+PMT structure. The designed RCSA outputs a step signal, thus enabling the acquisition of double-exponential signals with a stable time constant by using the next stage of a CR differentiating circuit. The designed RCSA is mainly composed of a basic amplifying circuit, a reset circuit and a dark current compensation circuit. It provides the output step signal through the integration of the PMT output charge signal. When the amplitude of the step signal exceeds a preset voltage threshold, it triggers the reset circuit to generate a reset pulse (about 5µs pulse width) to reset the output signal. Experimental results demonstrated that the designed RCSA achieves a charge sensitivity of 4.26×10(10)V/C, with a zero capacitance noise of 51.09fC and a noise slope of 1.98fC/pF. Supported by the digital shaping algorithm of the digital multi-channel analyzer (DMCA), it can maintain good energy resolution with high counting rates up to 150kcps and with a temperature range from -19°C to 50°C.
具有NaI(Tl)+PMT结构的传统伽马射线光谱仪前端读出电路输出信号的时间常数受温度、测量环境和信号传输电缆的影响，因此难以获得良好的分辨率谱，尤其是在较高计数率下。本文针对具有NaI(Tl)+PMT结构的伽马射线光谱仪设计了一种复位电荷灵敏放大器（RCSA）。所设计的RCSA输出一个阶跃信号，从而能够通过使用下一级CR微分电路采集具有稳定时间常数的双指数信号。所设计的RCSA主要由一个基本放大电路、一个复位电路和一个暗电流补偿电路组成。它通过对PMT输出电荷信号进行积分来提供输出阶跃信号。当阶跃信号的幅度超过预设电压阈值时，它触发复位电路产生一个复位脉冲（脉宽约5µs）来复位输出信号。实验结果表明，所设计的RCSA实现了4.26×10(¹⁰)V/C的电荷灵敏度，零电容噪声为51.09fC，噪声斜率为1.98fC/pF。在数字多道分析器（DMCA）的数字成形算法支持下，它在高达150kcps的高计数率和-19°C至50°C的温度范围内能够保持良好的能量分辨率。
