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

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 $\hat{I}\pm$-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 $6\times 10^{14}$ yr and $2\times 10^{16}$ 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 $1\times 10^{14}$ yr to $8\times 10^{16}$ yr. This improves the experimental information on some of the decay modes compared to previous constraints.