A compact gamma-ray detector for SPECT systems applied to BNCT dose monitoring

We present a compact gamma-ray detector, combined with a dedicated collimator and an appropriate shielding case, as a single unit to be assembled for the realization of a SPECT apparatus dedicated to dose monitoring and verification during BNCT treatments. The detector, based on a LaBr 3 (Ce+Sr) scintillator crystal readout by Silicon Photomultipliers (SiPMs) and compact electronics, features excellent energy resolution (<3% at 662 keV) and good detection efficiency (60% at 478 keV) that allow to detect the 478 keV gamma rays emitted by boron neutron capture reactions for real-time dose monitoring purposes. FLUKA simulations have been used to analyze the background signal nearby the BNCT photopeak induced by the neutron activation of the detector itself, a key issue in this application. The predominant contribution is due to the PCBs of the electronics readout. A dedicated cadmium shielding has been designed in order to improve the detector's sensitivity and reliability, while maintaining compact size, lower than 15×15×12 cm 3 , in view of the final ring configuration where many modules are required. The effectiveness of the shielding material, together with the capability of the detector to identify and resolve the BNCT signal, have been confirmed with experimental measurements at the TRIGA MARK II reactor of Pavia University.