Comparison of 6Li- and 7Li-induced fusion cross sections on 16O.

Abstract

The heavy residues emitted following the interaction of /sup 6/Li and /sup 16/O have been measured for /sup 6/Li bombarding energies from 12 to 35 MeV. The gross characteristics of the residue spectra are in qualitative agreement with a fusion-evaporation mechanism. Beginning at Coulomb barrier energies, it is found that the total fusion cross section diverges from the total reaction cross section obtained from optical model fits to /sup 6/Li+ /sup 16/O elastic scattering data. The importance of the process which limits the /sup 6/Li+ /sup 16/O fusion cross section is attested to by the fact that only 60% of the total reaction strength can be accounted for by fusion at our highest bombarding energies. A comparison of the total fusion cross sections as a function of center-of-mass energy for the /sup 6/Li+ /sup 16/O and /sup 7/Li+ /sup 16/O entrance channels reveals essentially identical total fusion cross section excitation functions. This result contrasts sharply with the results obtained in an earlier study of /sup 6,7/Li-induced reactions on /sup 12,13/C nuclei. In the earlier study, fusion cross sections which were projectile dependent and target independent were observed. Finally, the critical angular momenta have been extracted from the /sup 6/Li+ /supmore » 16/O total fusion cross sections. When compared with the critical angular momenta obtained from an earlier study of the /sup 10/B+ /sup 12/C entrance channel, a common limitation is found with increasing /sup 22/Na excitation energy. This result is in sharp contrast with the result of an earlier study of entrance channels which form the /sup 23/Na compound nucleus, a compound system only one neutron removed from /sup 22/Na.« less