Unnatural Parity States inO16. I

Abstract

A detailed study of the de-excitation of gamma emitting states in ${\mathrm{O}}^{16}$ at 8.87, 10.94, and 11.06 Mev has been carried out using the ${\mathrm{N}}^{14}({\mathrm{He}}^3, p\gamma ){\mathrm{O}}^{16}$ reaction. Branching ratios and angular distribution measurements on both proton groups and gamma radiations strongly suggest assignments $2^{-}$, $0^{-}$, and $3^{+}$, respectively, although in the latter case the $2^{-}$ possibility is not excluded. The experimental results are compared with predictions of the alpha-particle and intermediate-coupling shell models. While considerable areas of agreement exist, serious discrepancies remain in both cases. The identification of the $0^{-}$, 10.94-Mev state precludes Dennison's preferred "identification (a)" in the alpha-particle model and fixes the exchange mixture in the shell model calculations; the ${\mathrm{O}}^{16}$ mixture closely resembles a Serber rather than the Rosenfeld mixture commonly in use in these shell model calculations. From the measured de-excitation branching ratio $\frac{{\Gamma }_{\alpha }}{{\Gamma }_{\gamma }}$ for the 10.94-Mev state and the systematics of gamma-radiation and alpha-particle transition widths, an upper limit of ∼2×${10}^{-9\mathrm{}}$ is obtained for the relative intensity of an opposite-parity component in the wave function of this state.