High-spin states inRn214,Ra216and a study of even-evenN=128systematics

Abstract

High-spin states in $^{214}\mathrm{Rn}$ and $^{216}\mathrm{Ra}$ have been studied by means of the reaction $^{208}\mathrm{Pb}(^{13}\mathrm{C}, \ensuremath{\alpha}3n\ensuremath{\gamma})^{214}\mathrm{Rn}$ and $^{208}\mathrm{Pb}(^{13}\mathrm{C}, 5n\ensuremath{\gamma})^{216}\mathrm{Ra}$ at beam energies in the range 75-95 MeV. In-beam spectroscopy techniques, including $\ensuremath{\gamma}$-decay excitation functions, $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\gamma}$ coincidences, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidences, $\ensuremath{\gamma}$-ray angular distributions, and pulsed-beam-$\ensuremath{\gamma}$ timing, were utilized to establish level energies, $\ensuremath{\gamma}$-ray multipolarities, ${J}^{\ensuremath{\pi}}$ assignments, and isomeric lifetimes. Excited states with spins up to $23\ensuremath{\hbar}$ in $^{214}\mathrm{Rn}$ and $\ensuremath{\sim}30\ensuremath{\hbar}$ in $^{216}\mathrm{Ra}$ were observed. Isomers were found in $^{214}\mathrm{Rn}$ at 1625 keV (${T}_{\frac{1}{2}}=9$ ns, ${J}^{\ensuremath{\pi}}={8}^{+}$), 1787 keV (22 ns, ${10}^{+}$), 3485 keV (95 ns, 16), 4509 keV (230 ns, 20), and 4738 keV (8 ns, 22), and in $^{216}\mathrm{Ra}$ at 1708 keV (8 ns, ${8}^{+}$) and 5868 keV (10 ns, \ensuremath{\sim}24). $B(\mathrm{EL})$ values were deduced and compared to previously known lead-region electric transition rates. Shell-model calculations were performed and used to make configurational assignments. The absence of major $\ensuremath{\alpha}$-decay branching in the isomers is explained and the systematic behavior of $N=128$ even-even nuclei is discussed.NUCLEAR STRUCTURE $^{208}\mathrm{Pb}(^{13}\mathrm{C}, \ensuremath{\alpha}3n\ensuremath{\gamma})^{214}\mathrm{Rn}$, $^{208}\mathrm{Pb}(^{13}\mathrm{C}, 5n\ensuremath{\gamma})^{216}\mathrm{Ra}$, ${E}_{\mathrm{lab}}=75\ensuremath{-}95$ MeV. Measured $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\gamma}$ coin, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}(t)$ coin, $I(\ensuremath{\theta})$, pulsed-beam-$\ensuremath{\gamma}$ timing. Deduced level schemes, ${J}^{\ensuremath{\pi}}$, ${T}_{\frac{1}{2}}$, $B(\mathrm{EL})$, multipolarities. Shell model calculations, Ge(Li) and Si detectors, enriched target.