Simulation of background reduction and Compton depression in low-background HPGe spectrometer at a surface laboratory

TL;DR

This paper uses GEANT4 simulations to optimize background reduction in a low-background HPGe spectrometer, demonstrating significant environmental gamma ray suppression and improved spectral ratios through shielding and anti-coincidence techniques.

Contribution

The study presents a detailed simulation-based optimization of detector shielding and anti-coincidence configurations for low-background HPGe spectrometers, incorporating detailed detector descriptions and experimental validation.

Findings

Optimal BGO crystal thickness is 5.5cm for best performance.

Anti-coincidence efficiency of 0.85 raises Peak-to-Compton ratio to 1000.

Environmental gamma rays are reduced to 0.0024 cps/100cm³ Ge with shielding.

Abstract

High-purity germanium detectors are well suited to analysis the radioactivity of samples. In order to reduce the environmental background, low-activity lead and oxygen free copper are installed outside of the probe to shield gammas, outmost is a plastic scintillator to veto the cosmic rays, and an anti-Compton detector can improve the Peak-to-Compton ratio. Using the GEANT4 tools and taking into account a detailed description of the detector, we optimize the sizes of the detectors to reach the design indexes. A group of experimental data from a HPGe spectrometer in using were used to compare with the simulation. As to new HPGe Detector simulation, considering the different thickness of BGO crystals and anti-coincidence efficiency, the simulation results show that the optimal thickness is 5.5cm, and the Peak-to-Compton ratio of 40K is raised to 1000 when the anti-coincidence efficiency is 0.85. As the background simulation, 15 cm oxygen-free copper plus 10 cm lead can reduce the environmental gamma rays to 0.0024 cps/100 cm3 Ge (50keV~2.8MeV), which is about 10-5 of environmental background.