A kinematically complete study has been made of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}+{}_{}{}^{16}{}_{}{}^{}\mathrm{O}\to {}_{}{}^{12}{}_{}{}^{}\mathrm{C}+{}_{}{}^{12}{}_{}{}^{}\mathrm{C}+ \alpha$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}+{}_{}{}^{16}{}_{}{}^{}\mathrm{O}\to {}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}+ \alpha +\alpha$ reactions at $E_{{16}_{\mathrm{O}}}=58.3\mathrm{}$ MeV (lab). $\alpha$ particles were detected at a mean laboratory angle of 2°, while the remaining reaction products were observed in coincidence by two large-area position-sensitive detectors placed symmetrically about the beam axis and subtending angles in the range ${15}^{\circ }\le {\theta }_{\mathrm{lab}}\le {75}^{\circ }$. Particle identification was based on the reaction kinematics. Intense yields to the lowest four states of ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ were observed, with a significant fraction thereof proceeding through well defined intermediate states in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$. The predominant interaction in the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}+{}_{}{}^{12}{}_{}{}^{}\mathrm{C}+ \alpha$ final state appears to involve ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}+ \alpha$ corresponding to an excited state at ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ near 10 MeV excitation. No evidence was found for a ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$+${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ final state interaction, i.e., for quasimolecular states in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ in the region of excitation $21\le E^{*}\le 29$ MeV. The predictions of a Hauser-Feshbach statistical model agree rather well with the observed ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}+ \alpha +\alpha$ yields. A selected portion of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}+{}_{}{}^{12}{}_{}{}^{}\mathrm{C}+ \alpha$ yield, not necessarily proceeding through an excited state in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, is accounted for by a statistical model assuming formation and decay of compound states in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$.

[NUCLEAR REACTIONS ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^{16}{}_{}{}^{}\mathrm{O},{\alpha }_0{\alpha }_1){}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^{16}{}_{}{}^{}\mathrm{O},{\alpha }_0{}_{}{}^{12}{}_{}{}^{}\mathrm{C}_1^{}{}_{}{}^{}){}_{}{}^{12}{}_{}{}^{}\mathrm{C}_2^{}{}_{}{}^{}$, $E=58.3\mathrm{}$ MeV; measured $\sigma (E{\alpha }_{0,1}, E_{{20}_{\mathrm{Ne}}};{\theta }_{{\alpha }_1},{\theta }_{{20}_{\mathrm{Ne}}})$, $\sigma (E{\alpha }_0,E_{12{\mathrm{C}}_{1,2}};{\theta }_{12{\mathrm{C}}_{1,2}})$, $\theta {\alpha }_0=2^{\circ }$. Deduced intermediate $\alpha -{}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ interaction; Hauser-Feshbach analysis. Position-sensitive detectors.]

• Received 3 July 1973

DOI:https://doi.org/10.1103/PhysRevC.9.1474