Spin distributions in heavy ion fusion at and below the Coulomb barrier

The total cross section for compound nucleus formation at energies near the Coulomb barrier depends sensitively on the penetrability of the ion-ion potential. Many analyses of fusion data have relied on the parabolic approximation to account for the barrier penetration. There has been a great amount of interest recently in studying the details of fusion at and near the barrier. The penetrability of the barrier not only affects the energy dependence of the capture cross section, but the angular momentum dependence of the penetrability also determines the spin distribution brought into the compound nucleus during the capture. We have studied the energy dependence of the cross section and ..gamma.. multiplicity for the reactions ..cap alpha.., /sup 12/C, and /sup 16/O + /sup 154/Sm to determine the average properties of the spin distribution brought into the compound nucleus by fusion. Results are presented and discussed. (WHK)