Application of a high-precision distributed uranium source for determining the effective mass and volume of a HPGe detector

TL;DR

The paper demonstrates a high-precision, distributed $^{238}$U source approach to calibrate the effective mass and volume of a HPGe detector used in νGeN. By comparing homogeneous irradiation data with detailed Geant4 simulations, the authors verify that the detector's mass aligns with manufacturer specifications, obtaining an effective mass of $1.37 \pm 0.07$ kg against a nominal $1.42$ kg. The method highlights systematic sensitivities mainly to crystal positioning and internal geometry, while showing small contributions from source placement and dead-layer variations. This calibration technique supports precise neutrino interaction measurements and can extend to calibrations for enriched isotopes in future rare-decay experiments.

Abstract

A distributed uranium source with the accurately certified activity of 238U has been used to verify the effective mass of the HPGe detector intended for the νGeN neutrino experiment. The source, dissolved in nitric acid, provides homogeneous irradiation of the detector crystal allowing the study of its mass and volume. The experimental spectra obtained with the distributed source have been compared to the detailed Geant4 Monte Carlo simulations. The measured counting rates of several gamma-lines agree with the simulated efficiencies, confirming that the detector mass and volume coincide with the manufacturer specifications. The results demonstrate the applicability of such sources for mass calibration of HPGe detectors.

Figures (6)

• Figure 1: Simplified decay schemes of $^{238}$U and $^{235}$U NNDC.
• Figure 2: Visualization of uranium source placement on detector's endcap.
• Figure 3: Experimental spectra normalized to 24.4 h. Black: background measurements; blue: uranium source measurements; red: uranium after background subtraction.
• Figure 4: Comparison of experimental spectrum (black) and Geant4 simulations: $^{238}$U (blue), $^{235}$U (green), $^{238}$U+$^{235}$U (red).
• Figure 5: Fit of the peaks with function from arnquist2023energy.