Some Properties of the 2.98-MeV Level ofNa23

Abstract

Nuclear-resonance-fluorescence techniques have been used to measure the mean life of the 2.98-MeV level of ${\mathrm{Na}}^{23}$. The source of $\gamma$ rays was the decay of the 2.98-MeV level of ${\mathrm{Al}}^{27}$, as excited by inelastic scattering of 4.90-MeV protons. Using the branching ratio $\frac{{\Gamma }_0}{\Gamma }=0.56\mathrm{}\pm 0.06$, we find for the ground-state transition ${\Gamma }_0=\left(\frac{g_1}{g_2}\right)(77\mathrm{}\pm 12)\times {10}^{-3\mathrm{}}$ eV and for the total width $\Gamma =\left(\frac{g_1}{g_2}\right)(140\mathrm{}\pm 20)\times {10}^{-3\mathrm{}}$ eV, where $g_1$ and $g_2$ are the statistical weights for the ground and excited states. The mean life is then $\tau =\left(\frac{g_2}{g_1}\right)(4.7\mathrm{}\pm 0.8)\times {10}^{-15\mathrm{}}$ sec. We find the angular distribution for the resonance scattering to be $1+(0.87\pm 0.13)P_2\left(cos\theta \right)$. For the spin sequence $\frac{3}{2}-\frac{3}{2}-\frac{3}{2}$ this limits the $\frac{E2\mathrm{}}{M1\mathrm{}}$ amplitude ratio to $0.37<\mathrm{}\delta <1.43\mathrm{}$. For the sequence $\frac{3}{2}-\frac{5}{2}-\frac{3}{2}$, the limits are $-1.50<\delta <-1.14\mathrm{}$, $-0.47<\delta <-0.31\mathrm{}$, and $1.01<\mathrm{}\delta <1.82\mathrm{}$. This is not in agreement with other recent results on this level, and we have been unable to find a plausible explanation for the difference. Our smallest value of ${\delta }^2$ corresponds to a $B\left(E2\mathrm{}\right)\mathrm{}$ of approximately twice the single-particle value, $B{\mathrm{}\left(E2\mathrm{}\right)\mathrm{}}_{\mathrm{sp}}$.