Monte Carlo simulations for optimum design of composite detectors for high energy γ ray

The efficiencies of clover and cluster composite detectors using NaI and BGO crystals as the media for detection of high energy γ ray are systematically simulated with Monte Carlo method. It is shown that for the same geometry of detection media concerned the efficiency of the composite BGO detector is much higher than that of the composite NaI detector. Therefore NaI crystal is not a suitable medium of composite detectors for high energy γ ray duo to low efficiency. Doppler broadening and distortion to γ spectrum in comparison with BGO crystal. The composite BGO detectors have many advantages such as large photopeak efficiency, small Doppler effect and regular γ spectrum. As to the clover and cluster composite detectors consisting of the cylinders of BGO crystal with original size φ76 x 127, the intrinsic photopeak efficiencies are over 40% and the enhanced factor of absolute efficiencies is as high as 2.4 and 2.7, respectively, for 22 MeV γ ray