Abstract: Based on the integral expression of the efficiency of the high purity germanium detector, the full-energy peak linear attenuation coefficients are calculated theoretically. Combined with the different tracks of gamma photons in the detector, the Monte Carlo method is used instead of the numerical integration to obtain the expected value of the full-energy peak efficiency. Firstly, the full-energy peak efficiencies of N-type and P-type high purity germanium spectrometers at the axial position of 5 cm from the point source to the detector are simulated and verified. The deviations between the simulation results and the experimental results are within ± 5.24%, which prove the accuracy of the method for calculating the full-energy peak efficiency of point source. On the basis of the point source efficiency simulation, the full-energy peak efficiency of volume source is simulated by the efficiency transfer method. The method is verified by the standard sources of four different media, namely resin, silica, coffee ash and aerosol filter in the laboratory. Except for the relative large deviations at low energy regions of the P-type detector, the calculation deviations of the other energy detection efficiencies are less than ±6.67%. Compared with the whole-process Monte Carlo simulation method, this method does not require professional modeling programs and expensive commercial software, and can calculate the full-energy peak efficiencies of point sources and volume sources through simple programming, which has great practical significance for quantitative analysis of radioactivity under emergency conditions.

Key words: high-purity germanium detector, Monte Carlo, full-energy peak efficiency, γ spectrometer