Fusion cross section for 13C + 13C at low energies

Abstract

The energy dependence of the fusion cross section has been measured over the range E c.m. = 3.05–6.88 MeV by detecting the γ-rays from residual nuclei in a 4π geometry. Analyzing the 1.37 MeV photopeak, originating from 24 Mg 1.37 MeV → g.s. transition , the cross sections for 24Mg+2n channel were also deduced. The measured fusion cross sections have been compared with those for 12C + 12C and 12C + 13C systems and found to be significantly different. For 13C+ 13C the fusion cross sections agree with the standard optical-model prediction down to the lowest measured energies, while for 12C + 12C and 12C + 13C they are, at the lowest energies, too low. It is suggested that the unpaired valence nucleons facilitate fusion at energies well below the Coulomb barrier.