SCoTSS modular survey spectrometer and compton imager

We present the development of a mobile survey spectrometer and fieldable Compton gamma-ray imager. The detector employs CsI(Tl) scintillator coupled to SensL silicon photomultipliers (SiPMs) and incorporates a unique modular design, where individual units can be employed separately in applications requiring a compact detector, e.g. military operations, or combined together for those requiring a more sensitive detector, e.g. aerial surveying. Each module is a fully functional imager, providing both mapping and imaging capabilities along with isotope detection and identification. We describe the design of an imager module, its custom electronics readout, its integration into the Radiation Solutions Inc (RSI) RadAssist software, and its performance in the lab and field. The energy reconstruction is shown to perform well across the full spectrum of interest up to 3 MeV, with resolutions and noise levels suitable for low-energy measurement in both the scatter and absorber parts of the detector. Successful truck-borne field tests of the imager demonstrate that it is capable of localizing a shielded 10 mCi Cs-137 source at distances up to 40 m to within a few degrees in tens of seconds.