Study of the germanium dead layer influence on HP(Ge) detector efficiency by Monte Carlo simulation

Abstract

The dead layer thickness provided by the manufacturer increases with the aging of the HPGe detector; the increase of dead layer thickness leads to the decrease in the detector’s efficiency, not only due to gamma rays attenuation in the dead layer but also due to the reduction of the active volume of the detector. In this work, the dead layer influence on HPGe detector efficiency was studied by Monte Carlo simulation. The detector model was developed using Monte Carlo N Particle (MCNP5) code for adjustment of the dead layer thickness; the adjustment was performed according to a specific irradiation configuration by collimation approach using three reference point sources: 241Am (59.5 keV), 137Cs (661.6 keV) and 60Co (1173.2 keV; 1332.5 keV). The calculated efficiencies were compared to the measured intrinsic efficiency ones for these point sources; a good agreement between Monte Carlo and measurements results was found after the experimental validation. The results confirm the variation in the dead layer thickness according to aging of the detector; the average change of dead layer is in order of 1.30 ± 0.05 mm after 9 years.