Excitation functions and thick target recoil ranges for radioactive nuclei produced in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ bombardment of ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$ over a 5–50 MeV/nucleon energy range have been measured using the activation technique. At 81 and 118 MeV ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ energy, the angular distributions of the radioactive recoils were also measured. Using the in-beam gamma ray technique, production cross sections for many radioactive as well as stable residual nuclei were measured for the ${}_{}{}^4{}_{}{}^{}$He${+\mathrm{}}^{59}$Co system for a ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ energy range between 30 and 150 MeV. Close to 90% of the reaction cross section was observed over the entire energy range. From the experimental data, information about the energy and linear momentum deposition in the interaction of He projectiles with the Co target was gathered. Two distinct changes in the reaction mechanism are apparent at about 40 and 90 MeV bombarding energies, as manifested by observables related to the energy and momentum deposition. The change of the reaction mechanism at 40 MeV is related to the onset of preequilibrium α-particle and nucleon emission. The nature of the mechanism change which sets in at 90 MeV is less well understood.

• Received 25 November 1985

DOI:https://doi.org/10.1103/PhysRevC.34.60