First search for $2\epsilon$ and $\epsilon {\beta }^{+}$ decay of ${}^{162}$Er and new limit on $2{\beta }^{-}$ decay of ${}^{170}$Er to the first excited level of ${}^{170}$Yb

Abstract

The first search for double electron capture ($2\epsilon$) and electron capture with positron emission ($\epsilon {\beta }^{+}$) of ${}^{162}$Er to the ground state and to several excited levels of ${}^{162}$Dy was realized with 326 g of highly purified erbium oxide. The sample was measured over 1934 h by the ultra-low background HP Ge $\gamma$ spectrometer GeCris (465 cm${}^3$) at the Gran Sasso underground laboratory. No effect was observed, the half-life limits were estimated at the level of $\lim T_{1/2}\sim 10^{15}-10^{18}$ yr. A possible resonant $0\nu K{L}_1$ capture in ${}^{162}$Er to the $2^{+}$ 1782.7 keV excited state of ${}^{162}$Dy is restricted as $T_{1/2}\ge 5.0\times 10^{17}$ yr at 90% C.L. A new improved half-life limit $T_{1/2}\ge 4.1\times 10^{17}$ yr was set on the $2{\beta }^{-}$ decay of ${}^{170}$Er to the $2^{+}$ 84.3 keV first excited state of ${}^{170}$Yb.

23 pages, 6 figures and 4 tables