A large HPGe detector for the non-destructive radioassay of an ultra-low-background counting facility

TL;DR

This paper describes a low-background HPGe detector setup and its application in non-destructive radioassay, achieving high accuracy in measuring trace U, Th, and K in PMTs for neutrino experiments.

Contribution

The paper introduces a large, low-background HPGe detector with detailed Monte Carlo modeling for precise radioassay of complex components.

Findings

Achieved ~10 ppb accuracy for U and Th measurements.

Achieved ~15 ppm accuracy for K measurements.

Successfully measured radioisotope contents in PMTs used in neutrino experiments.

Abstract

We present the use of a low background counting facility, equipped with a p-type 80% relative efficiency HPGe detector, protected by active and passive shielding, and large enough to count a 10" photo-multiplier tube (PMT). A GEANT4 Monte-Carlo of this detector was developed and tuned to 3% accuracy. We report the U, Th, and K contents in three different types of PMTs used in current neutrino experiments, with accuracies of $\sim 10$ ppb for U and Th and of $\sim 15$ ppm for K.