Search for rare alpha and double beta decays of Yb isotopes to excited levels of daughter nuclei

TL;DR

This study searched for rare alpha and double beta decays of ytterbium isotopes into excited nuclear states using a low-background germanium detector, setting new experimental limits on their half-lives.

Contribution

It provides the first experimental constraints on these decay modes and improves existing limits for certain double electron capture and double beta decay processes.

Findings

Half-life limits between 6×10^{14} and 2×10^{16} years for alpha decays.

Limits between 1×10^{14} and 8×10^{16} years for double electron capture and double beta decay.

First constraints on these decay modes for Yb isotopes.

Abstract

A search for alpha and double beta decays of ytterbium isotopes was performed with an ultra-low background high purity germanium detector at Gran Sasso Underground Laboratory (Italy). A 194.7 g Yb$_2$(C$_2$O$_4$)$_3$ powder sample was measured for 11.3~d with a total Yb exposure of 1.25 kg$\times$d. Half-life limits for $\alpha$-decay modes of $^{168}$Yb, $^{170}$Yb, $^{171}$Yb, $^{172}$Yb, $^{173}$Yb, $^{174}$Yb and $^{176}$Yb into the first excited states have been obtained between $6\times10^{14}$ yr and $2\times10^{16}$ yr. These are the first experimental constraints of these decay modes. Double electron capture of $^{168}$Yb and double beta decay of $^{176}$Yb into the first excited 2$^+$ and 0$^+$ states could be excluded with limits between $1\times10^{14}$ yr to $8\times10^{16}$ yr. This improves the experimental information on some of the decay modes compared to previous constraints.