The ${}^{150}$Nd(${}^3$He,$t$) and ${}^{150}$Sm($t$,${}^3$He) reactions with applications to ${\hat{I}}^2{\hat{I}}^2$ decay of ${}^{150}$Nd

Abstract

The ${}^{150}$Nd(${}^3$He,$t$) reaction at 140 MeV/u and ${}^{150}$Sm($t$,${}^3$He) reaction at 115 MeV/u were measured, populating excited states in ${}^{150}$Pm. The transitions studied populate intermediate states of importance for the (neutrinoless) ${\hat{I}}^2{\hat{I}}^2$ decay of ${}^{150}$Nd to ${}^{150}$Sm. Monopole and dipole contributions to the measured excitation-energy spectra were extracted by using multipole decomposition analyses. The experimental results were compared with theoretical calculations obtained within the framework of Quasiparticle Random-Phase Approximation (QRPA), which is one of the main methods employed for estimating the half-life of the neutrinoless ${\hat{I}}^2{\hat{I}}^2$ decay ($0\hat{I}½{\hat{I}}^2{\hat{I}}^2$) of ${}^{150}$Nd. The present results thus provide useful information on the neutrino responses for evaluating the $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ and $2\hat{I}½{\hat{I}}^2{\hat{I}}^2$ matrix elements. The $2\hat{I}½{\hat{I}}^2{\hat{I}}^2$ matrix element calculated from the Gamow-Teller transitions through the lowest $1^{+}$ state in the intermediate nucleus is maximally about half of that deduced from the half-life measured in $2\hat{I}½{\hat{I}}^2{\hat{I}}^2$ direct counting experiments and at least several transitions through $1^{+}$ intermediate states in ${}^{150}$Pm are required to explain the $2\hat{I}½{\hat{I}}^2{\hat{I}}^2$ half-life. Because Gamow-Teller transitions in the ${}^{150}$Sm($t$,${}^3$He) experiment are strongly Pauli-blocked, the extraction of Gamow-Teller strengths was complicated by the excitation of the $2\hslash \ddot{I}‰$, $\hat{I}”L=0$, $\hat{I}”S=1$ isovector spin-flip giant monopole resonance (IVSGMR). However, the near absence of Gamow-Teller transition strength made it possible to cleanly identify this resonance, and the strength observed is consistent with the full exhaustion of the non-energy-weighted sum rule for the IVSGMR.

18 pages, 13 figures, 2 tables