Double beta decay of $^{150}$Nd to the first 0$^+$ excited level of $^{150}$Sm
Résumé
An experiment to measure the 2$\beta{^-}$ decay of $^{150}$Nd to excited levels of $^{150}$Sm using a highly purified 2.381 kg sample of Nd$_2$O$_3$ is in progress in the low-background set-up with 4 HPGe detectors (~225 cm$^3$ volume each). The detector is located deep underground (3600 m w.e.) at the STELLA facility of the Gran Sasso National Laboratory (LNGS) of the INFN (Italy). Two γ quanta with energies 334.0 keV and 406.5 keV emitted after deexcitation of the 0$_1 {^+}$ excited level of 1$^{50S}$m have been observed in the experimental data accumulated over 39898 h. The preliminary half-life value for 2$\beta{^-}$ decay of $^{150}$Nd to the first 0$^+$ excited level in $^{150}$Sm (after the exposure of 10.8 kg $\times$ yr) was estimated as $T_{1/2}=[9.7{{+2.9}\atop{-1.9}}(stat.) {\pm}1.5(syst.)]\times 10^{19}$ yr. The experiment is under data taking with the aim to improve the statistical uncertainties.