Preliminary results of an experiment to detect $\gamma$ transitions between the high energy particle unstable structures known in the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ system are reported. The specific process investigated is (${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$) 25.8 MeV (c.m.) → $\gamma$ + (${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$) 19.3 MeV (c.m.) → $\gamma$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ (g.s. or $2^{+}$). The initial energy is near the center of the gross structure thought to have $J^{\pi }={14}^{+}, \mathrm{and} 19.3$ MeV is the energy of the ${12}^{+}$ intermediate width resonance. An upper limit (one standard deviation) is found ${\left(\frac{{\Gamma }_{\gamma }}{\Gamma }\right)}_{25.8 \mathrm{Mev}}\lesssim \left(2\mathrm{} \mathrm{to} 8\right)\times {10}^{-6\mathrm{}}$ depending on the analysis procedure. This result shows there is no collective $\gamma$ decay between the intermediate width resonances at the energies studied here, and is comparable in size and consistent with resonance-fragmentation models but does not exclude nonresonant ones.

NUCLEAR REACTIONS Compared ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ → $\gamma$ + (${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$) and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$($2^{+}$) + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$($2^{+}$) $\sigma$'s; $E_{\mathrm{lab}}=25.8\mathrm{}$ MeV; deduced $\frac{{\Gamma }_{\gamma }}{\Gamma }$ upper limit.

• Received 15 July 1981

DOI:https://doi.org/10.1103/PhysRevC.24.2374