A STUDY OF THE EFFICIENCY DISTRIBUTION OF THE LOW BACKGROUND GAMMA SPECTROMETER USING THE HPGe DETECTOR

Abstract

In the measurement of environmental samples with low radioactivity by the low background gamma spectrometer system using the high purity germanium (HPGe) detector, it is often interested to enhance the detector efficiency for minimizing the measurement time and thus improving the quality of gamma spectra. The source geometry shaped cylinder and Marinelli is widely used to satisfy the purposes as above but the scientific basis of choosing these types of source have been not set up generally. In this study, the MCNP5 code was used to simulate the gamma spectrum of the point source positioned a certain location in the sample measurement space of the gamma spectrometer and the detector efficiency was computed to determine the efficiency distribution. Additionally, this efficiency distribution was also investigated when to change the gamma energy and the matrix density. The results showed that there are two high efficiency regions on the top and around the lateral of the detector. This results agree with the viewpoint of selecting the right cylindrical and Marinelli geometries.