Properties of the 4.431-MeV Excited State ofNa23

Using the Doppler-broadened 4.43-MeV gamma line from the reaction ${\mathrm{N}}^{15}(p, \alpha ){\mathrm{C}}^{12*}$ as the exciting radiation, resonance fluorescence from the 4.431-MeV level in ${\mathrm{Na}}^{23}$ has been observed. The 4.431-MeV ground-state transition, accounting for (95±3)% of the de-excitations, exhibits an isotropic angular distribution. This fact and the absence of branching to the 0.44-MeV $\frac{5}{2}+$ level make ½ the most probable spin assignment. With this spin value, a self-absorption study leads to a partial width ${\Gamma }_0=(2.14\mathrm{}\pm 0.10)$eV for the ground-state transition. When this width is combined with the observed branching, a total width $\Gamma =(2.25\mathrm{}\pm 0.20)$eV is obtained for the 4.431-MeV level in ${\mathrm{Na}}^{23}$, which is found to populate also the 2.39 MeV excited state in (5±3)% of its decays. A comparison of scattering and self-absorption data for different values of the ratio of natural width to Doppler width confirms the spin assignment of ½ to the 4.431-MeV level, which might be the first member of the $K=\frac{1}{2}-$ band based on the Nilsson orbit 14. For a value $\eta =+4\mathrm{}$ of the deformation parameter, the $E1\mathrm{}$ transition probability calculated with Nilsson wave functions agrees with the experimental value.