The excitation function for the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${}_{}{}^3{}_{}{}^{}\mathrm{He}$, ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$) reaction has been measured up to incident energies of 31 MeV, and the ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ recoil properties determined in a series of catcher foil experiments at 30 MeV. Based on the different recoil properties of ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ formed by each of four different mechanisms, the contribution of each has been estimated. At 30 MeV the predominant mode of ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ formation is through sequential decay of the compound nucleus ${\left[{}_{}{}^{15}{}_{}{}^{}\mathrm{O}\right]}^{*}\to {\left[{}_{}{}^{11}{}_{}{}^{}\mathrm{C}\right]}^{*}+{\alpha }_1\to {}_{}{}^7{}_{}{}^{}\mathrm{Be}+{\alpha }_2+{\alpha }_1$ (≅39 mb). This is followed in importance by the direct $n$ pickup reaction to certain excited states in ${}_{}{}^{11}{}_{}{}^{}\mathrm{C}$ followed by $\alpha$-particle emission ${\left[{}_{}{}^{11}{}_{}{}^{}\mathrm{C}\right]}^{*}\to {}_{}{}^7{}_{}{}^{}\mathrm{Be}+\alpha$. The direct $\alpha$ particle pickup reaction and compound nucleus evaporation of ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$ have smaller cross sections (≅1 mb and ≫1 mb, respectively).

NUCLEAR REACTIONS ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(${}_{}{}^3{}_{}{}^{}\mathrm{He}$, ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$), $E\le 31$ MeV; measured $\sigma (E,\theta )$; deduced reaction mechanisms.

• Received 7 April 1975

DOI:https://doi.org/10.1103/PhysRevC.13.2116