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| Development of Digital X-Ray Fluorescence Spectrometer With Low Accidental Coincidence Effect |
| WANG Zhong-tao, HE Li, HU Chuan-hao, BAI Bin, GU Min, ZENG Guo-qiang*, GE Liang-quan, YAN Lei, YANG Shou-nan |
| College of Nuclear Technology and Automation Engineering, Chengdu University of Technology, Chengdu 610059, China |
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Abstract In the measurement of the X-ray fluorescence spectrum, when the interval between the two cases is short, there is a rising or falling edge pulse pile-up. If the pulse resolution of the spectrometer is not enough, the accidental coincidence effect occurs when the event interval is less than the pulse resolution of the spectrometer. When the pulse pile-up occurs on the rising edge of the signal, the next stage electronics is hard to identify the pile-up pulses and regards them as a single pulse，leading to the coincidence peaks and incorrect spectrum measurement. When the pulse pile-up appears at the falling edge, and the pile-up pulse interval is shorter than the digital shaping time of the multichannel pulse amplitude analyzer, the pile-up pulse will be discarded and lead to the reduction of spectrum count and cause a low throughput rate，which has a negative effect on the precision of radioactivity measurement. In this paper, increasing the signal-to-noise ratio of the analog circuit, reducing the false trigger and shortening the forming time of the fast forming channel, so as to improve the pulse resolution ability of the spectrometer and reduce the coincidence effect, a digital spectrometer of the fast and slow dual forming channel with low accidental coincidence effect is developed. The energy spectrometer has designed a fast channel with high pulse resolution. Based on the symmetrical zero area trapezoid forming algorithm, it can effectively eliminate the shortcomings caused by the narrowing of fast channel time, combined with the judgment of the trapezoidal flat top, the low-frequency noise suppression and error reduction are realized trigger probability. At the same time, the analog circuit with high signal-to-noise ratio and low noise is designed to reduce the probability of false noise triggering and an accidental coincidence of fast channel. In this paper, firstly, the fast channel time enhancement ability is verified by simulation, and then Cu samples were excited through the X-ray tube created by Moxtek to obtain characteristic X-rays, and the signal is detected by the high-resolution SDD detector of KETEK. The tube current of the X-ray tube was adjusted to acquire X-ray fluorescence spectra with a count rate ranging from 13 to 103 kcps and determine the relationship between the probability of accidental coincidence and count rate. Then, the influence of the shaping time change of the fast channel on accidental coincidence was analyzed. Experiments showed that a short fast-channel shaping time resulted in high pulse pair resolution and low accidental coincidence effect. At a 103 kcps count rate, under the fast-channel shaping time of 150 ns, the accidental coincidence probabilities of the Kα, Kβ, and Kα+Kβ combination peaks of Cu were 1.568%, 0.265%, and 0.403%, respectively. Under the same fast-channel shaping time, the accidental coincidence probability of the proposed digitized digital spectrometer was 60% lower than that of the DP-5 digital spectrometer produced by Amptek.
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Received: 2019-12-31
Accepted: 2020-03-18
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Corresponding Authors:
ZENG Guo-qiang
E-mail: zgq@cdut.edu.cn
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