An upper limit (three standard deviations) of 8×${10}^{-6\mathrm{}}$ has been determined for the branching ratio of gamma to particle decay of the ${14}^{+}$ resonance at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=25.2\mathrm{}$ MeV in the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ system. This limit is a factor of 2-3 lower than theoretically expected for an interpretation of the intermediate structure resonances as quasimolecular states in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$, making this hypothesis unlikely. The experimental limit is consistent with an interpretation of these structures as shape resonances in a direct reaction process.

NUCLEAR REACTIONS ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ elastic and inelastic scattering; measured ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$-${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ coincidences, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$-${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$-$\gamma$ triple coincidences; deduced upper limit on $\gamma$ decay of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ resonances.

• Received 26 June 1981

DOI:https://doi.org/10.1103/PhysRevC.25.1486