Abstract

In this paper the MCNP4C2 code was applied to investigate the effect of increase of the inactive germanium layer of the GC1518 HPGe detector at the Center for Nuclear Techniques Ho Chi Minh City. The calculation and experimental results showed that the inactive germanium layer of this detector was determined to be 1,16 ±0,07 mm at present compared to the initial value of 0.35 mm in 1996. The increase of inactive germanium layer can be considered as a main reason for decreasing detector efficiency of about 8% from October 1999 to November 2005. The calculation results of gamma spectra of 137Cs and 60Co sources based on MCNP4C2 code with the inactive germanium layer of 1.16 mm were in agreement with experimental spectra better than those performed inactive germanium layer of 0.35 mm, published in our previous work.