Search for triple and quadruple $\beta$ decay of $^{150}$Nd
Résumé
Triple β decay of Nd150 to the ground and excited states of Eu150 and quadruple β decay of Nd150 to the excited states of Gd150 have been studied using a 400 cm3 low-background high-purity germanium detector and an external source consisting of 3046 g of natural Nd2O3 powder. A half-life limit for the quadruple β decay to the 01+ state of Gd150 was found to be T1/2(0ν+4ν)>8.7×1020 yr (90% C.L.). For other (0ν+4ν) transitions to the 21+, 31−, 41+, 22+, and 23+ excited states limits have been obtained for the first time at the level of (6.1–9.5)×1020 yr (90% C.L.). We report here also the results for the first search for triple β decay to the ground and excited final states of Eu150. We find no evidence of this decay and set lower limits on the half-life in the range T1/2(0ν+3ν)>(0.04−4.8)×1020 yr (90% C.L.).