Simultaneous experimental evaluation of pulse shape and deadtime phenomenon of GM detector

Bader Almutairi,Syed Alam,Tayfun Akyurek,Cameron S Goodwin,Shoaib Usman

doi:10.1038/s41598-021-81571-3

Abstract

Analysis of several pulse shape properties generated by a Geiger Mueller (GM) detector and its dependence on applied voltage was performed. The two-source method was utilized to measure deadtime while simultaneously capturing pulse shape parameters on an oscilloscope. A wide range of operating voltages (600–1200 V) beyond the recommended operating voltage of 900 V was investigated using three radioactive sources (204Tl, 137Cs, 22Na). This study investigates the relationship between operating voltage, pulse shape properties, and deadtime of the detector. Based on the data, it is found that deadtime decreases with increasing voltage from 600 to 650 V. At these low voltages (600–650 V), the collection time was long, allowing sufficient time for some recombination to take place. Increasing the voltage in this range decreased the collection time, and hence deadtime decreased. It is also observed that rise and fall time were at their highest at these applied voltages. Increasing the voltage further would result in gas multiplication, where deadtime and pulse width are observed to be increasing. After reaching the maximum point of deadtime (~ 250 µs at ~ 700 V), deadtime started to exponentially decrease until a plateau was reached. In this region, it is observed that detector deadtime and operating voltage show a strong correlation with positive pulse width, rise and fall time, cycle mean, and area. Therefore, this study confirms a correlation between detector deadtime, operating voltage, and pulse shape properties. The results will validate our hypothesis that deadtime phenomena at different operating voltages are phenomenologically different.

Highlights

Researchers have been using Geiger Mueller (GM) counter for almost a century[1]
Two factors contribute toward the deadtime of a radiation detection system: (I) the inherent deadtime of the detector itself known as intrinsic deadtime, and (II) the collective deadtime that results from pulse processing instruments[8]
The general belief that for any GM counter pulse amplitude, pulse shape, and deadtime is constant for the entire operating voltage range is incorrect, as recently shown by Akyurek[7] and Almutairi[19]

Summary

Introduction

Researchers have been using Geiger Mueller (GM) counter for almost a century[1]. To detect and record two independent radiation events, there has to be a minimum time interval between two radiation events. Several deadtime models have been proposed for count rate corrections of the radiation detection system. For count rate correction consideration, there are two traditional deadtime models: (1) the paralyzing, and (2) non-paralyzing models These two idealized models are employed extensively in the industry and academia. The paralyzing model assumes that each radiation event taking place within the detector would extend the resolving time (deadtime). The non-paralyzing model (known as non-extending type) is based on the assumption that each radiation event taking place within the detector will be followed by deadtime. Unlike the paralyzing model’s assumption of continuous paralysis of the detector when a radiation event is detected, the non-paralyzing model assumes that the detector is dead only for a fixed time following the detection of a radiation event. The mathematical expression for the non-paralyzing model is given in Eq (2)

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Conclusion