A count correction method for multistage dead time in gamma-ray spectrometry

Abstract

Count loss at high count rates, caused by the minimum time required for pulse processing, is inevitable for spectroscopic systems. Thus count correction is needed to restore the distorted counting information. Such correction is based on the knowledge of the system behavior. In this study, the count loss mechanism of the gamma-ray spectrometer was modeled as a cascade of extending dead time (EDT) and pileup rejection (PUR). The cascade results in a reduce in the characteristic dead time, demonstrated by the simulation. For dead times in series, count correction is normally difficult in that Poisson properties are distorted after events passing through the first dead time. Therefore, we provided a new perspective to understand the time interval distribution of a dead time. Also, a new dead time model for PUR was developed for the purpose of count correction. Based on these, the cascade of EDT and PUR were factorized into three subsystems. The count correction factor for the multistage dead time is given by individually finding it for each subsystem. The correction method was tested in the simulation and implemented in our spectrometer. In the simulation, the proposed method was proved to be theoretically correct, without distinct deviation. When tested using a detector emulator, a maximum system error of 0.6% emerged. The error, though well acceptable under 95% pulse loss, may be attributed to that the first stage dead time cannot be ideally modeled as EDT.