Random coincidence summing of gamma rays and dead time count loss corrections in HPGe-detector based gamma ray spectrometry

Abstract

Random coincidence summing of gamma rays and dead time count losses are a potential source of errors in gamma ray spectrometry. In this work, the magnitudes of count rate losses due to the random coincidence summing and dead time effect, alongwith corresponding corrections, have been studied. Experiments were performed in two independent gamma ray spectroscopic laboratories (referred as LAB-A & LAB-B), utilizing low activity reference nuclides 65 Zn and 60 Co. The low activity reference radionuclide 65 Zn was produced by using 10 MW nuclear reactor (PARR-1) at PINSTECH for use in one Lab. The gamma ray spectra were acquired using HPGe-detector based gamma ray spectrometers at fixed shaping times of the amplifier and positions of the reference nuclides. The MCA dead times of the spectrometers were varied to incur the count rate losses to the peaks of interest. Three procedures were adopted to determine the dead time and random summing correction factors. The corrections to count rate data measured at LAB-A, which represented a maximum of 46% losses, were obtained within standard deviation figures of 2.9%, 1.3% and 0.4% and in LAB-B case the losses of 41%, were corrected to within 1.8%, 1.1% and 0.6%, respectively with the described three procedures. The best-achieved precision (difference between the measured count rate with negligible dead time and the average of corrected count rates) in the case of LAB-A and LAB-B were within 1 x 10 ―3 and 2 x 10 ―2 %. The new procedure on the basis of fitting function is also evolved as a result of this study, which has produced the highly consistent results. The experimental data from the literature are also incorporated in this study for comparison purposes.