Tomography gamma scanning(TGS) technology is an important method for accurate determination of transuranic nuclides in medium-and high-density heterogeneously distributed media

hence the importance of determining the detection efficiency of a TGS.This can be done by a sourceless calibration based on Monte Carlo method.In this paper

a simulation model is established with a 6×6×6 sample division and the GR3091 HPGE system

and the relationship of spatial symmetry is used to save computer hours.Comparisons between the calculation and the measurement results prove that the computer simulation is a good method.