Mechanism of the O16(Li7,)F19 reaction at 20 MeV

The O16(Li7)F19 reaction has been investigated at an incident energy of 20 MeV. Complete angular distributions were measured in the angular range lab=7.5°-157.5°using a multiangle spectrograph. Known (sd)3 states are populated about twice as strongly as the core-excited four-particle "one-hole (4p-1h) states. Angular distributions for members of the ground-state band show only a moderate forward-angle rise and those of the negative-parity band and other weak states are approximately symmetric around 90°. Results have been analyzed in terms of Hauser-Feshbach compound-nucleus calculations and finite-range distorted-wave Born approximation calculations in which the three transferred nucleons enter the sd and/or 1p shells. The contribution of the compound-nucleus cross section has been estimated. The data for the K=12 and K=12 bands in F19 could be well fitted by an incoherent sum of direct and compound reaction cross sections. Simple analysis of the integrated cross sections based on a (2J+1) rule is consistent with results of the Hauser-Feshbach calculations. Comparison between the present experimental results and previous triton cluster transfer reactions on O16 emphasizes the enhanced compound/direct ratio for the 4p-1h and other weak states in the present data.