Search for triple and quadruple beta decay of ${}^{150}$Nd

Abstract

Triple beta decay of ${}^{150}$Nd to the ground and excited states of ${}^{150}$Eu and quadruple beta decay of ${}^{150}$Nd to the excited states of ${}^{150}$Gd have been studied using a 400 cm${}^3$ low-background HPGe detector and an external source consisting of 3046 g of natural Nd${}_2$O${}_3$ powder. A half-life limit for the quadruple beta decay to the 0${}_1^{+}$ state of ${}^{150}$Gd was found to be $T_{1/2}(0\hat{I}½+4\hat{I}½)>8.7\times 10^{20}$ yr (90\% C.L.). For other (0$\hat{I}½$+4$\hat{I}½$) transitions to the 2${}_1^{+}$, 3${}_1^{-}$, 4${}_1^{+}$, 2${}_2^{+}$ and 2${}_3^{+}$ excited states limits for the first time have been obtained at the level of $(6.1-9.5)\times 10^{20}$ yr (90\% C.L.). We report here also the results for the first search for triple beta decay to the ground and excited final states of ${}^{150}$Eu. We find no evidence of this decay and set lower limits on the half-life in the range $T_{1/2}(0\hat{I}½+3\hat{I}½)>(0.04-4.8)\times 10^{20}$ yr (90\% C.L.).

8 pages, 9 figures, 2 tables. arXiv admin note: text overlap with arXiv:0904.1924