Nuclear Structure ofNa22. V. Doppler-Shift Attenuation Measurements

The mean lifetimes of seven nuclear levels of ${\mathrm{Na}}^{22}$ have been measured by the Doppler-shift attenuation method. The ${\mathrm{F}}^{19}(\alpha ,n){\mathrm{Na}}^{22}$ reaction was used to populate the levels. $\gamma$ rays were observed at 0° to the $\alpha$ beam with a Ge(Li) detector. The results, when averaged with previous work, yield the following mean lives (in psec) for the indicated levels: 0.891 (12.25±1.75), 1.528 (3.5±0.6), 1.984 (1.74±0.34), 2.211 ($20_{-8\mathrm{}}^{}{}_{}{}^{+25\mathrm{}}$), 2.572 (5.7±0.9), 2.969 (0.060±0.013), and 3.059 (0.040±0.01), where the levels are designated by their excitation energies (in MeV). For the five lowest levels the lifetimes were obtained from an analysis of Doppler-shifted line shapes; the remaining two lifetimes were determined from conventional centroid-shift analysis. The latter method also gave a lifetime of 5.2±0.9 psec for the 1.346-MeV level of ${\mathrm{F}}^{19}$. Some information was obtained on the $\frac{M2\mathrm{}}{E1\mathrm{}}$ mixing ratios of the ground-state and first-excited-state transitions from the $J^{\pi }=2^{-} 2.572-$MeV level of ${\mathrm{Na}}^{22}$. Evidence for a $K=1\mathrm{}$ odd-parity rotational band in ${\mathrm{Na}}^{22}$ is discussed.