Structure ofN=81nuclei: Levels ofNd141andCe139populated in beta decay

Abstract

The nuclear level structure of $^{141}\mathrm{Nd}$ and $^{139}\mathrm{Ce}$ has been investigated by studying the decay of 20.9-min $^{141}\mathrm{Pm}$ produced via the $^{141}\mathrm{Pr}(^{3}\mathrm{He},3n)$ reaction and the decay of 4.5-h $^{139}\mathrm{Pr}$ produced by the $^{140}\mathrm{Pr}(\ensuremath{\gamma},n)^{139}\mathrm{Pr}$ reaction. For the $^{141}\mathrm{Pm}$ decay, singles and anti-Compton $\ensuremath{\gamma}$-ray spectra and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence measurements were used to deduce a decay scheme that includes nine previously unreported levels in $^{141}\mathrm{Nd}$ and incorporates 67 of the 70 $\ensuremath{\gamma}$ rays attributed to the decay of $^{141}\mathrm{Pm}$. Singles and anti-Compton spectra were taken as a function of time in order to confirm assignment of the $^{139}\mathrm{Pr}$ $\ensuremath{\gamma}$ rays. The level structures of $^{141}\mathrm{Nd}$ and $^{139}\mathrm{Ce}$ are compared to recent measurements in other $N=81$ isotones. The results of this work are in good agreement with theoretical predictions based on the hole-vibrational coupling model for levels below 1.3 MeV. There exist more levels between 1.3 and 2.0 MeV than are predicted by this model, but these excess levels can be explained qualitatively within a weak coupling framework.RADIOACTIVITY $^{141}\mathrm{Pm}$ [from $^{141}\mathrm{Pr}(^{3}\mathrm{He},3n)$] and $^{139}\mathrm{Pr}$ [from $^{140}\mathrm{Pr}(\ensuremath{\gamma},n)$] measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coin; deduced $^{141}\mathrm{Nd}$ and $^{139}\mathrm{Ce}$ levels, $J$, $\ensuremath{\pi}$, and $log\mathrm{ft}$ values. Natural target, Ge(Li) detectors, anti-Compton spectrometer.