Abstract: By using Monte Carlo method,the authors simulated the scintillation of γ ray with different energy into the BGO crystal and the  position distribution of scintillation photons with different thickness and package.The results show that the model of point light source is suitable to the distribution of scintillation photons on production interface of the crystal.Furthermore,the position resolution of photons for rough interface between BGO and seal is much better than for polished interface.The nearer the distance of scintillation center from light-out plane is,the narrower spatial resolution of optical photon is.Finally,the author obtained the most number of output photons when the thickness of BGO is 4 mm.

Key words: Monte Carlo；photon production；scintillation；&gamma, imaging