counts are simulated by the Code of Geant4 and the variable separation method. When using different substrate materials，

the ratio between the backscattering peak and full-energy peak counts，as well as the simulated saturation

thicknesses of different materials are in agreement with the experimental results. The backscattering peak counts as

functions of the thickness of scintillator packaging material，as well as the length，the cross-sectional area and the

volume of scintillator are also simulated，and the method to suppress the backscattering peak background is found.