High count-rate digital gamma-ray spectroscopy using a low-cost COTS digitizer system

Abstract

A combination of publicly-available digitizers (COTS) has been used in digital gamma-ray spectroscopy in recent years. In this work, a feasibility study was undertaken to use a personal computer (PC) sound card as a digitizer in digital gamma-ray spectroscopy with NaI(Tl) scintillation detector. To this end, the duration of the output pulses of the NaI detector was increased to 300 μs by the preamplifier. Also, the algorithms for correcting and rejecting pile-up events at a low sample rate (96 kHz) were investigated. A new method based on a high-pass filter was developed to detect the pulse start time. Moreover, a new fast-fitting method based on the Integrodifferential equation was introduced, which represented a good performance at a low sample rate. An approximate method of applying the MLE method of long waveforms was also implemented. Wong's method was analytically rewritten assuming that there were more neighbors and it was shown that this result was independent of the assumption of a different number of close neighbors. The performance of these three methods in correcting the energy spectrum of the Cs-137 source, which was disturbed due to the presence of pile-up events and achieving high energy resolution, was compared. Finally, a new method based on the full width at half maximum of preamplifier pulses was also introduced to reject pile-up events.