The population of the 6.05-MeV $0^{+}$ state in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ in the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ reaction was measured for $E_{\mathrm{lab}}\left({}_{}{}^{16}{}_{}{}^{}\mathrm{O}\right)=46\mathrm{}-56$ MeV by detecting the $0^{+}$ → g.s. pair transition. ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ recoil pair and $\gamma$ coincidence spectra were obtained at the $L=14\mathrm{}$ resonance at 46.3 MeV to obtain the relative population of the 6.13-MeV $3^{-}$and 6.05-MeV $0^{+}$ states. The total pair cross section reveals resonances at $E_{\mathrm{lab}}=48, 51.4, 52.9, \mathrm{and} 55.5$ MeV which are correlated with resonances seen in other channels. The ratio of resonant cross sections $\frac{\sigma \left(0^{+}\right)}{\sigma \left(3^{-}\right)}$ varies between 0.014 and 0.080. Reduced widths extracted for the $0^{+}$ excitation channel are of the same order as those of the $3^{-}$ and 6.92-MeV $2^{+}$ final state channels. This indicates that the weak $0^{+}$ cross section is caused by the energy-angular-momentum mismatch rather than by the structure of the resonance wavefunction.

NUCLEAR REACTIONS ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$($0^{+}$, 6.05 MeV)) ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, $E=46\mathrm{}-56$ MeV, detect $e^{+}-e^{-}$ pairs; measure $\sigma \mathrm{}\left(E\right)\mathrm{}$, deduce resonances, reduced widths.

• Received 22 December 1977

DOI:https://doi.org/10.1103/PhysRevC.17.2097