Measurement of fusion cross sections for 14N + 14N and 12C + 16O at low energles

Abstract

Total fusion cross sections for 14N + 14N and 12C + 16O have been measured for bombarding energies extending from the Coulomb barrier down to E c.m. ≈ 4.6 MeV. Absolute cross sections were deduced from the yields of individual γ-ray transitions observed with a Ge(Li) detector and a statistical-model calculation of the decay modes of the compound nucleus. This technique was checked by a detailed comparison of the present results for 12C + 16O with the earlier results of Patterson et al. for charged particle decay, with the study of Spinka and Winkler of activation following neutron emission, and with the measurements of Čujec and Barnes on total γ-ray emission. The present method for determination of the total fusion cross section was found to compare very favourably with other methods. The gross energy dependence of the fusion cross section for 14N + 14N was observed to be similar to that of 12C + 16O. In contrast to 12C + 16O, however, the cross section does not exhibit any resonant-like structure. A simple barrier-penetration model employing the incoming-wave boundary condition is able to reproduce the observed fusion cross section for 14N + 14N. An analysis of the transfer reaction 14N( 14N, 13N) 15N at sub-barrier energies is also presented and a comparison is made between the direct and compound reactions.