Eur. Phys. J. C (2023) 83: 1114
https://doi.org/10.1140/epjc/s10052-023-12218-y

Regular Article - Experimental Physics

First search for resonant enhanced neutrinoless double electron capture in ${}^{152}$Gd and other rare decays in natural Gd isotopes

¹ INFN-Laboratori Nazionali del Gran Sasso, 67100, Assergi, (AQ), Italy
² Nuclear Science Division, Lawrence Berkeley National Laboratory, 94720, Berkeley, CA, USA
³ Department of Physics, Engineering Physics and Astronomy, Queen’s University, 64 Bader Lane, K7L 3N6, Kingston, ON, Canada
⁴ Arthur B. McDonald Canadian Astroparticle Physics Research Institute, 64 Bader Lane, K7L 3N6, Kingston, ON, Canada

^b bjoernlehnert@lbl.gov
^c sn65@queensu.ca

Received: 3 March 2023
Accepted: 6 November 2023
Published online: 8 December 2023

Abstract

A first 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 ${\text{Gd}}_2$${\text{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 enhanced neutrinoless double electron capture which could significantly increase the decay rate over other neutrinoless double beta decay processes. The half-life for this decay was constrained to $>4.2\times {10}^{12}$ year (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 ${10}^{17-20}$ year.