GM counter deadtime dependence on applied voltage, operating temperature and fatigue

This paper utilized standard two-source method and the simple non-paralyzing model assumption to examine a GM counter's deadtime dependence on applied voltage, operating temperature, and fatigue. Both ⁶⁰Co and ¹³⁷Cs sources were used for deadtime measurements. The results gathered suggest the presence of three distinct regions of deadtime behavior. At low voltages, the deadtime decreases as the voltage increases (Region I) followed by a region of stable deadtime plateau (Region II) and finally a region of increasing deadtime with increasing voltage. Region II is the best region for operating with a minimum deadtime which is not sensitive to the applied voltage. Typical deadtime values for GM counters were between 100 and 300 μs; the deadtime values in Region II were within this range. The results examined in this study also indicate a strong temperature dependence of deadtime, with a correlation coefficient of 0.93. The GM counter deadtime for various fatigues (aging) were investigated for three fatigue levels with a correlation coefficient of 0.48. The experimental results confirm that deadtime increases as both temperature and fatigue increase. The fundamental nature of deadtime seems to be different for voltages lower than the stable deadtime plateau (Region II) and for voltages higher than the plateau.