Proton-Induced Activation of New Scintillator Materials: SrI, GAGG, CLLB, CLLBC, TLYC, CLYC-7

Abstract

In recent years, a number of new scintillator materials with improved energy resolution for gamma-ray detectors have become commercially available for use in terrestrial-based homeland security applications, and some are being incorporated into instrumentation for space. Unlike terrestrial applications, the harsh environment of space—in particular, energetic trapped particles, cosmic rays, and neutrons—often activates these materials, and any improvement in sensitivity as a result of improved energy resolution could be offset by the additional background due to activation. The purpose of this work was to measure potential backgrounds due to trapped and cosmic-ray proton-induced activation in the new materials: SrI₂:Eu (SrI), ⁷Li-enriched Cs₂LiYCl₆:Ce (CLYC-7), Cs₂LiLaBr₆:Ce (CLLB), Cs₂LiLa(Br,Cl)₆:Ce (CLLBC), Tl₂LiYCl₆:Ce (TLYC), and Gd₃(Al,Ga)₅O₁₂:Ce (GAGG). Using a large-diameter 64-MeV proton beam, detectors were irradiated with a total dose of 100 rad (Si), roughly equivalent to the annual dose in a typical low earth orbit. Measurements were made with a single 100% relative efficiency high-purity germanium (HPGe) (0.05–3 MeV) and the irradiated detector. Two multichannel analyzers (MCAs) operating in the event mode were used to collect the data. Time-tagged events were processed into various spectral integration times for analysis, and characteristic gamma-ray energies and decay times were used to identify activation products. Most of the identified activation products were the result of (p, xn) reactions, with a few exceptions. This work identifies the primary radioisotopes generated by energetic proton activation in six different scintillator materials.