Detector design for high-resolution MeV photon imaging of cargo containers using spectralinformation

Monte Carlo simulations of a pixelated detector array of inorganic scintillators for high spatial resolution imaging of 1-9 MeV photons are presented. The results suggest that a detector array of 0.5 cm×0.5 cm×5 cm pixels of bismuth germanate may provide sufficient efficiency and spatial resolution to permit imaging of an object with uncertainties in dimension of several millimeters. The crosstalk between pixels is found to be in the range of a few percent when pixels are shielded by ∼1 mm of lead or tungsten. The contrast at the edge of an object is greatly improved by rejection of events depositing less than ∼1 MeV. Given the relatively short decay time of BGO, the simulations suggest that such a detector may prove adequate for the purpose of rapid scanning of highly shielded cargos for possible presence of high atomic number (including clandestine fissionable) materials when used with low current high duty factor X-ray sources.