Nuclear size and boundary effects on the fusion barrier of oxygen with carbon

Abstract

Absolute yields, energy spectra, and angular distributions of heavy residual nuclei ranging from Ne to Si have been measured in the reactions ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, and ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$. For each system measurements have been performed at seven beam energies corresponding to the range 7 to 14 MeV c.m. The formation of the above products is shown to be consistent with a reaction which proceeds through the formation and decay of an excited and equilibrated composite system. Systematic differences between the absolute magnitudes of the fusion cross sections of the three reactions have been observed. It is shown that these differences are closely related to the expected differences in the nuclear size and surface diffuseness of the oxygen isotopes. Possible implications for astrophysical processes are briefly discussed.