Prog Med Phys.  2022 Dec;33(4):129-135. 10.14316/pmp.2022.33.4.129.

Dead Layer Thickness and Geometry Optimization of HPGe Detector Based on Monte Carlo Simulation

• Yu S
• Kwon NH
• Jang YJ
• Lee B
• Yu J
• Kim DW
• Cho GS
• Kim KB
• Kim GB
• Baek CH
• Choi SH

• KMID: 2537881
• DOI: http://doi.org/10.14316/pmp.2022.33.4.129

Abstract

Purpose
A full-energy-peak (FEP) efficiency correction is required through a Monte Carlo simulation for accurate radioactivity measurement, considering the geometrical characteristics of the detector and the sample. However, a relative deviation (RD) occurs between the measurement and calculation efficiencies when modeling using the data provided by the manufacturers due to the randomly generated dead layer. This study aims to optimize the structure of the detector by determining the dead layer thickness based on Monte Carlo simulation.
Methods
The high-purity germanium (HPGe) detector used in this study was a coaxial p-type GC2518 model, and a certified reference material (CRM) was used to measure the FEP efficiency. Using the MC N-Particle Transport Code (MCNP) code, the FEP efficiency was calculated by increasing the thickness of the outer and inner dead layer in proportion to the thickness of the electrode.
Results
As the thickness of the outer and inner dead layer increased by 0.1 mm and 0.1 µm, the efficiency difference decreased by 2.43% on average up to 1.0 mm and 1.0 µm and increased by 1.86% thereafter. Therefore, the structure of the detector was optimized by determining 1.0 mm and 1.0 µm as thickness of the dead layer.
Conclusions
The effect of the dead layer on the FEP efficiency was evaluated, and an excellent agreement between the measured and calculated efficiencies was confirmed with RDs of less than 4%. It suggests that the optimized HPGe detector can be used to measure the accurate radioactivity using in dismantling and disposing medical linear accelerators.

Keyword

HPGe detector; Dead layer; Monte Carlo simulation; Full-energy-peak efficiency

Figure

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  Fig. 1 Internal structure (a) and section of the high-purity germanium (HPGe) detector in the MC N-Particle Transport (MCNP) code (b). CRM, certified reference material.

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  Fig. 2 Energy and full width half maximum (FWHM) obtained by gamma-ray spectroscopy.

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  Fig. 3 Relative difference between the measured and calculated values according to the dead layer thickness.

Reference

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