Rotational Band Structure ofNa22. I. Electromagnetic Transitions for Levels ofEex<4.0MeV

Abstract

Electromagnetic transitions from levels of $^{22}\mathrm{Na}$ which belong to the rotational bands ${K}^{\ensuremath{\pi}}={3}^{+},{0}^{+}$ ($T=0$) and ${1}^{\ensuremath{-}}$ have been studied by the $^{19}\mathrm{F}(\ensuremath{\alpha},n\ensuremath{\gamma})^{22}\mathrm{Na}$ reaction. Lifetimes have been measured by the recoil distance method (RDM) and by the Doppler-shift attenuation method (DSAM). From a comparison of the results obtained by the two methods, the stopping powers for $^{22}\mathrm{Na}$ in the stopping materials used have been deduced. The adopted lifetimes $\ensuremath{\tau}$ (ps) for the levels studied [${E}_{\mathrm{ex}}$ (MeV), ${J}^{\ensuremath{\pi}}$] are the following: 14.7 \ifmmode\pm\else\textpm\fi{} 0.7 [0.891, ${J}^{\ensuremath{\pi}}={4}^{+}$], 4.8 \ifmmode\pm\else\textpm\fi{} 0.3 [1.528, ${J}^{\ensuremath{\pi}}={5}^{+}$], 0.077 \ifmmode\pm\else\textpm\fi{} 0.020 [3.708, (${J}^{\ensuremath{\pi}}={6}^{+}$)], 2.40 \ifmmode\pm\else\textpm\fi{} 0.35 [1.984, ${J}^{\ensuremath{\pi}}={3}^{+}$], 21.2 \ifmmode\pm\else\textpm\fi{} 1.0 [2.211, ${J}^{\ensuremath{\pi}}={1}^{\ensuremath{-}}$], 8.8 \ifmmode\pm\else\textpm\fi{} 0.9 [2.572, ${J}^{\ensuremath{\pi}}={2}^{\ensuremath{-}}$], and 0.64 \ifmmode\pm\else\textpm\fi{} 0.16 [3.521, ${J}^{\ensuremath{\pi}}={3}^{\ensuremath{-}}$]. New branches for the $\ensuremath{\gamma}$-ray decay of the 1.984- and 2.572-MeV levels have been observed. The negative parity of the levels at 2.572 and 3.521 MeV has been definitively established. The electro-magnetic properties, of some of these levels, have been compared with the isobaric spin selection rules for $N=Z$ nuclei, with the predictions of the unified model of Nilsson and with recent shell-model calculations.