Year
2016
Abstract
Ambient temperature radiation detectors which exhibit high resolution and efficiency are vital for the verification and analysis of special nuclear material. BiI3, a layered compound with a band gap of 1.67 eV, features the attractive physical and electronic properties needed to serve in material monitoring and assay instrumentation. Recently, it was demonstrated that reduction in macroscopic defects, which arise as an artifact of crystal growth, can dramatically increase the ability of BiI3 to produce signal from gamma rays. Prior detector samples of BiI3 have been limited to sensing low energy (< 100 keV) gamma rays, likely due to defects quenching all signals except for those which interact in the volume close to the sensing electrode. Now, by modifying the crystal growth process, crystals with vastly improved electrical and spectral properties have been prepared and gamma ray detectors with larger active volumes are made possible from the improved crystal quality. In this presentation we report spectra can now be collected and analyzed from Bridgman-grown Sb:BiI3 sensors, which now show spectral response with gamma rays from sources such as 241Am, 57Co, 133Ba, 137Cs, 153Gd, and 60Co. These new high- quality crystals of BiI3 detectors exhibit good resolution (7.1% at 662 keV), and collection capability after samples have been biased in excess of 100 hours. This enhanced material is attractive for a variety of in-field safeguards applications such as holdup measurements. Included is a comparison of holdup scenario simulations, showcasing the attractiveness of this material in comparison to other room temperature spectrometers such as NaI(Tl) and CdZnTe. Additionally, a discussion of the ruggedness of this crystal, and how inert surface coatings may be utilized to enhance the lifetime of crystals is included.