Gadolinium is widely used in multiple low-background experiments, making its isotopes accessible for rare decay searches both in-situ and through radiopurity screening data. This study presents an improved search for rare alpha and double-beta decay modes in 152Gd, 154Gd, and 160Gd isotopes using ultra-low background HPGe detectors at the Boulby Underground Screening (BUGS) facility. A total exposure of 6.7 kg⋅yr of natural gadolinium was achieved using gadolinium sulfate octahydrate (Gd2(SO4)3⋅8H2O) samples, originally screened for radiopurity prior to their deployment in the Super-Kamiokande neutrino experiment. Due to the detection methodology, only decays into excited states accompanied by gamma-ray emission were accessible. A Bayesian analysis incorporating prior experimental results was employed, leading to new lower half-life limits in the range of 1019−1021 years - an improvement of approximately two orders of magnitude over previous constraints. No statistically significant decay signals were observed. These results demonstrate the effectiveness of repurposing large-scale radiopurity screening campaigns for fundamental physics research.
@article{arxiv.2503.01641,
title = {Improved sensitivity in the search for rare decays of Gd isotopes},
author = {B. Lehnert and S. S. Nagorny and M. Thiesse and F. Ferella and M. Laubenstein and E. Meehan and S. Nisi and P. R. Scovell},
journal= {arXiv preprint arXiv:2503.01641},
year = {2025}
}