Experimental studies of the resonance atEc.m.=19.7MeV in theC12+O16system

Abstract

A resonance appearing in the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ system at a center-of-mass incident energy of 19.7 MeV has been studied experimentally. Excitation functions for the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ inelastic scattering and the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^{16}{}_{}{}^{}\mathrm{O}, \alpha ){}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}_{}^{*}{}_{}{}^{}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^{16}{}_{}{}^{}\mathrm{O}, p){}_{}{}^{27}{}_{}{}^{}\mathrm{Al}_{}^{*}{}_{}{}^{}$ reaction channels were measured. The width of the resonance was shown to be more than double the average level width in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ at excitation energies around 36.5 MeV where this resonance appears. The resonance is enhanced at large angles in the elastic and inelastic channels and it is found to be equally strong at ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}=3\mathrm{}° \mathrm{and} 177°$ for the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^{16}{}_{}{}^{}\mathrm{O}, p){}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ reaction. The yield of 6.13 MeV $\gamma$ radiation has been measured and is observed to resonate at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=19.7\mathrm{}$ MeV. High resolution measurements of the particle yield at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=19.7\mathrm{}$ MeV, ${\theta }_{\mathrm{lab}}=7.5\mathrm{}°$ for the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$)${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$* (6.05, 6.13 MeV) show that the $3^{-}$ (6.13 MeV) state is populated much more strongly than the $0^{+}$ (6.05 MeV) state. These results do not support the suggestion that the resonance has a ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$-$\alpha$-${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ molecular structure. Measurements of inelastic scattering at higher energies suggest the existence of additional correlated structures. A statistical analysis of the $\alpha$-particle yields indicates that both compound and direct mechanisms contribute to the reaction. A discussion of the properties of the resonance in terms of intermediate structure and the statistical theory of Moldauer is given.