Search for Rare Nuclear Decays with HPGe Detectors at the STELLA Facility of the LNGS

TL;DR

This paper reports on the search for rare nuclear decays using ultra low background gamma spectrometry at the STELLA facility, setting new limits and observing rare decay modes in various isotopes.

Contribution

It presents the first investigation of several isotopes for double beta decay and resonant processes, and reports the first observation of rare alpha decay of 190Pt.

Findings

Best half-life limits for double beta processes in 96Ru and 104Ru.

First-time investigation of multiple isotopes for double beta decay.

First observation of rare alpha decay of 190Pt.

Abstract

Results on the search for rare nuclear decays with the ultra low background facility STELLA at the LNGS using gamma ray spectrometry are presented. In particular, the best T1/2 limits were obtained for double beta processes in 96Ru and 104Ru. Several isotopes, which potentially decay through different double beta decay channels, including also possible resonant double electron captures, were investigated for the first time (156Dy, 158Dy, 184Os, 192Os, 190Pt, 198Pt). Search for resonant absorption of solar 7Li axions in a LiF crystal gave the best limit for the mass of 7Li axions (< 8.6 keV). Rare alpha decay of 190Pt to the first excited level of 186Os (Eexc = 137.2 keV) was observed for the first time.