Search for resonant neutrinoless double electron capture in Gd-152 and other rare decays in Gd isotopes

TL;DR

This study searches for rare decay processes in gadolinium isotopes, especially resonant neutrinoless double electron capture in Gd-152, setting new experimental limits and guiding future research in this area.

Contribution

First experimental limit established on resonant neutrinoless double electron capture in Gd-152, advancing the search for rare nuclear decay processes.

Findings

Half-life for Gd-152 neutrinoless double electron capture >4.2×10^{12} years

Set limits on other rare alpha and double beta decays in Gd isotopes

Demonstrated feasibility of ultra-low background detection in underground labs

Abstract

A search for rare decays of gadolinium isotopes was performed with an ultra-low background high-purity germanium detector at Gran Sasso Underground Laboratory (Italy). A 198 g Gd$_2$O$_3$ powder sample was measured for 63.8 d with a total Gd exposure of 12.6 kg$\times$d. $^{152}$Gd is the most promising isotope for resonant neutrinoless double electron capture which could significantly enhance the decay rate over other neutrinoless double beta decay processes. The half-life for this decay was constrained to $>4.2\times10^{12}$ yr (90\% credibility). This limit is still orders of magnitude away from theoretical predictions but it is the first established limit on the transition paving the way for future experiments. In addition, other rare alpha and double beta decay modes were investigated in $^{152}$Gd, $^{154}$Gd, and $^{160}$Gd with half-life limits in the range of $10^{17-20}$ yr.