Characterization of strontium iodide scintillators with silicon photomultipliers

Abstract

This work characterizes a commercially available europium-doped strontium iodide detector recently developed by Radiation Monitoring Devices (RMD). The detector has been chosen for a space-based mission scheduled to launch in early 2017. The primary goal of this work was to characterize the detector׳s response over the expected operational range of −10°C to 30°C as well as the expected operational voltage range of +26.5–+28.5V and identify background interferences that may develop due to neutron activation produced by cosmic-ray interactions. The 8mm×8mm×20mm detectors use KETEK silicon photomultipliers (SiPM), with an active area of 6mmx6mm (KETEK PM6660). Our results show substantial integral nonlinearity due to the SiPM ranging from 0% to 25% at room temperature over the energy range of 80–2614keV. The nonlinearity, a function of temperature and overvoltage, leads to an underestimate of the full width at half max (FWHM), which is 2.6% uncorrected at 662keV and 3.8% corrected at 662keV. The temperature dependence of the detector results in a noise threshold that increases substantially above 30°C due to the SiPM dark rate. In an effort to simulate the harsh environment of space, neutron activation of the detector was also explored. Gamma-ray lines at 127keV and 164keV were observed in the detector along with Kα x-rays associated with europium. Beta decay from europium- and iodine-activation products were also observed within the detector.