Experimental HPGe coaxial detector response and efficiency compared to Monte Carlo simulations

Re-construction of a HPGe detector precise modeling for efficiency calibration

High purity germanium (HPGe) detector is a preferred choice for determining the activity of the radioactive samples for nuclear diagnostics of Inertial Confinement Fusion (ICF) experiments. Although the amounts of the radiochemical sample are limited, activity measurement at a close distance between the detector window and the radioactive source is a feasible method. Efficiency calibration of gamma rays at a close distance from the surface of a HPGe detector is crucial. Considering the problem of the coincidence at a close distance, the alternative way is to construct a precise model of the HPGe detector and then to calculate efficiency accurately at an arbitrary distance from the surface of the HPGe detector using Monte Carlo method. In this paper, internal geometry and structure except for dead layers of the HPGe detector is obtained by X-ray radiography and 3D reconstruction. The optimal dead layers of the germanium crystal are determined by tracing the minimal sum squared residual (SSR) of gamma-ray efficiencies between calculations and measurements for standard planar sources. Nonhomogeneous distribution of the dead layer is supposed according to the inner structure on the Ge crystal. The final results show that the corrected model improves the accuracy of the calculated efficiencies.

An automated programme for the optimisation of HPGe detector parameters using an evolutionary algorithm with GESPECOR

We describe the development of an automated, user-friendly programme which, making use of the GESPECOR gamma spectrometry software to conduct Monte Carlo simulations, yields an optimised model of a HPGe detector by applying suitable optimisation algorithms without requiring any further user intervention. The programme is capable of simultaneously employing multiple experimental FEP efficiency curves for the parameter optimisation process. Application of the optimisation process to a HPGe detector demonstrates that accurate, robust models can be achieved using this approach.

Validation of gamma scanning method for optimizing NaI(Tl) detector model in Monte Carlo simulation

The aim of this study is the validation of gamma scanning method for optimizing NaI(Tl) detector model in Monte Carlo simulation. The experimental procedure involved: scanning on front and lateral surfaces of the detector with collimated low-energy photon beam; calibrating the efficiency with energies between 31-1408 keV for point sources at distances of 0 cm and 30 cm from source to the detector. The Monte Carlo code used for the simulations was MCNP6. The diameter and the length of crystal were determined according to the measured results of gamma scanning with a collimated ²⁴¹Am radioactive source. The distance from window to crystal was estimated using transmission measurement recorded on a second detector. The density of reflector was adjusted to obtain the match between measured and simulated values of efficiency ratio of 81 and 31 keV from a ¹³³Ba radioactive source. The optimized model was applied in Monte Carlo simulations to determine the efficiency and energy spectrum response function of NaI(Tl) detector for point source measurements in two configurations. Good agreement was obtained between measured and simulated results.