Unnatural Parity States in ${\mathrm{O}}^{16}$. II

Measurements on both proton and gamma angular distributions and on proton-gamma angular correlations from the ${\mathrm{N}}^{14}({\mathrm{He}}^3, p\gamma \gamma )$ reaction suggest that for an incident energy of 2.1 Mev and target thicknesses corresponding to between 200 and 350 kev for these ${\mathrm{He}}^3$ ions, the excited states of ${\mathrm{O}}^{16}$ are formed with equally populated magnetic substates. A number of gamma-gamma angular correlations have been studied from this reaction; these support the hypothesis of equal substate populations for the 8.87-, 10.94-, and 11.06-Mev states. On this hypothesis, the quadruple angular correlations studied reduce to effective double gamma-gamma correlations which are amenable to much simpler analysis. Using this hypothesis, gamma-gamma angular correlation data have been used in conjunction with the data on the relative gamma-ray de-excitation probabilities of the excited states of ${\mathrm{O}}^{16}$ to fix the spins and parities of the levels at 8.87, 10.94, and 11.06 Mev as $2^{-}$, $0^{-}$, and $3^{+}$, respectively. In addition the multipole amplitude ratios have been obtained for a number of the transitions involved in the calculations; these are used to calculate $M1\mathrm{}$ inhibition factors expected for $\Delta T=0\mathrm{}$ transitions in self-conjugate nuclei and these in turn are compared with the theoretical estimates for this inhibition. Where intermediate-coupling shell model predictions are available for the multipole mixtures they are also compared with the experimental results; an anomalously low value of the depth of the central potential used in these calculations is required for agreement.