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

## TL;DR

This study searched for rare triple and quadruple beta decays of $^{150}$Nd using a low-background detector, setting new lower limits on their half-lives and finding no evidence of these decays.

## Contribution

First experimental limits on quadruple and triple beta decay half-lives of $^{150}$Nd to various excited states were established.

## Key findings

- No evidence of triple or quadruple beta decay was observed.
- New lower half-life limits were set, reaching up to $8.7 imes 10^{20}$ years.
- Limits for the first time on certain excited state transitions were obtained.

## 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 $T_{1/2} (0\nu+4\nu) > 8.7\times10^{20}$ yr (90\% C.L.). For other (0$\nu$+4$\nu$) 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 $(6.1-9.5)\times10^{20}$ 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 $T_{1/2} (0\nu+3\nu) > (0.04-4.8)\times10^{20}$ yr (90\% C.L.).