PNNL

Abstract

Spectroscopic gamma-ray detectors are used for many research applications, as well as Homeland Security screening applications. Sodium iodide (NaI) scintillator crystals coupled with photomultiplier tubes (PMTs) provide medium-resolution spectral data about the surrounding environment. NaI based detectors, paired with spectral identification algorithms, are often effective in identifying sources of interest by isotope. However, intrinsic limitations exist for NaI systems because of gain shifts and spectral marring (e.g., loss of resolution and count-rate saturation) at high count rates. These effects are hardware dependent, and have strong effects on the radioisotopic identification capability of these systems. In this work, the effects of high count rate on the capability of isotope identification algorithms are explored. It is shown that a small gain shift of a few tens of keV is sufficient to disturb identification. The onset of this and other spectral effects are estimated for several systems., and a mechanism for mitigating these effects by estimating and correcting for them is implemented and evaluated.