Investigating the Impact of Source Geometry and Distance on HPGe Detector Efficiency Using MCNPX Simulations

The most important characteristic of HPGe detector is its efficiency, which depends on the geometry of the source and the detector material. Normally, efficiency is function of the gamma energy and must be determined for each specific material that is subject of the measurements. This requires secondary standard for each material, and it is expensive and time-consuming process. Monte Carlo method can be helpful as an alternative computational method to calculate the efficiency of HPGe detector. This paper describes a procedure for constructing a Monte Carlo model of an HPGe detector used to measure activity. In this work, the HPGe detector was completely simulated by MCNPX computational code according to the laboratory conditions and geometry of the Marinelli source. Comparison has shown the average difference of about 10% between the experimental and the Monte Carlo simulation efficiency of the HPGe detector. The detector efficiency for the source in cylindrical geometry with various dimensions and different distances between the source and the detector was calculated and studied.