Reset charge sensitive amplifier for NaI(Tl) gamma-ray spectrometer. (March 2015)

• Record Type: Journal Article
• Authors: Zeng, Guoqiang; Tan, Chengjun; Li, Qiang; Ge, Liangquan; Liu, Xiyao; Luo, Qun
• Is Part Of: Applied radiation and isotopes. Volume 97(2015:Mar.)
• Page Start: 63
• Page End: 69
• Publication Date: 2015-03
• Subjects: NaI(Tl) gamma-ray spectrometer -- Photomultiplier tube (PMT) -- Reset charge sensitive amplifier (RCSA) -- Equivalent noise charge (ENC); Radiology -- Periodicals; Radiation -- Industrial applications -- Periodicals; Nuclear chemistry -- Periodicals; Internet resource; Periodical; 660.298
• DOI: 10.1016/j.apradiso.2014.12.009
• Languages: English
• ISSNs: 0969-8043

Abstract

Abstract: 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 5 µs 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 51.09 fC and a noise slope of 1.98 fC/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 150 kcps and with a temperature range from −19 °C to 50 °C. Highlights: A new reset type charge sensitive amplifier for gamma-ray spectrometer based on a photomultiplier tube is proposed. Reset circuit formed by constant current source output a fixed width pulse to reset charge sensitive amplifier. Photomultiplier tube dark current compensation circuit could increase the pulse through rate by decreasing reset frequency. This amplifier outputs a step function signal that could match next stage circuit easily.