A model-independent method for mitigation of pileup artefacts in energy-resolved radiation counting

Abstract

This article presents a model-independent post-processing method to restore the counting and spectral information of pulse-height analyzers in the presence of pulse pileup at high counting rates. The method is based on the measurement of counts and of the integral durations of the detector signals over different thresholds, and on the comparison of the measurements from two sources with the same energy distribution and different counting rates $\rho$. The procedure does not require the modeling of the pulse shape, the knowledge of the dead-time $\tau$ or other parameters. The correction technique was validated with simulations and with spectra of high activity gamma sources collected with a high-purity germanium (HPGe) detector. For a simulated flat energy distribution and a ratio 2 between the two counting rates, the relative mean deviation between the corrected and input spectra is less than 1% and the relative standard deviation below 5% up to a normalized input rate $\rho \tau =1.0$. These results improve by increasing the difference between the input rates of the two sources. In the simulation of an X-ray spectrum at a normalized input rate $\rho \tau =0.5$, the ratio between the number of corrected and generated counts in each energy bin is below a few percent. The experimental validation was performed by acquiring two spectra of ${}^{241}$Am sources of different activities placed in a fixed position and of a high activity ${}^{137}$Cs source placed in two different position. In both cases, the correction method provides count rate distributions in close agreement with a reference spectrum from a lower activity source. The mitigation of artefacts in HPGe spectra overcomes the performance of a standard pileup rejection method.