Correction of pulse-height spectra for peak pileup effects using periodic and random pulse generators

Abstract

Peak pileup decrease the counting efficiency and distorts the recorded spectral shape in a pulse-height spectroscopy system. To correct for counting efficiency, it is common to estimate the photon detector input count rate by adding a pulse generator peak, wth known count rate, to a spectrum. A rigorous set of equations is developed to predict the number of piled up counts when either a periodic or a random pulser is used. Using these equations and an empirical treatment of ADC dead-time, expressions for the input count rate are derived for two cases: (1) “sparse” spectra dominated by one or a small number of photon peaks, and (2) “dense” spectra in which photon events occupy most of the spectral channels. Only the first has been treated previously. We provide formulae for the second case both for the situation where the pulser peak is superimposed on the photon region, and where it is separate from the photon region. The pileup equations are incorporated in an iterative routine which corrects for spectral distortion. The analysis has been applied to spectra of 99mTc and medical bremsstrahlung, measured with a high-purity germanium spectroscopy system.