Aluminum as a source of background in low background experiments

TL;DR

This paper investigates how aluminum used in germanium detector surface metallization can contribute to background noise in low-background experiments, emphasizing the need for careful aluminum selection to minimize interference in neutrinoless double beta decay searches.

Contribution

It identifies specific radioactive isotopes in aluminum that affect background levels and suggests criteria for selecting aluminum to reduce background in high-sensitivity experiments.

Findings

Radioactive isotopes in aluminum can contribute to background noise.

Careful selection of aluminum can mitigate background contributions.

Background levels depend on the specific isotopic composition of aluminum.

Abstract

Neutrinoless double beta decay would be a key to understanding the nature of neutrino masses. The next generation of High Purity Germanium experiments will have to be operated with a background rate of better than 10^-5 counts/(kg y keV) in the region of interest around the Q value of the decay. Therefore, so far irrelevant sources of background have to be considered. The metalization of the surface of germanium detectors is in general done with aluminum. The background from the decays of 22Na, 26Al, 226Ra and 228Th introduced by this metalization is discussed. It is shown that only a special selection of aluminum can keep these background contributions acceptable.