Possible evidence for exchange effects in theO16(Li6,α)F18reaction atELi6 =34MeV

Abstract

Fifty-four-point angular distributions in the angular range 2.5/sup 0/ to 170/sup 0/ have been measured for the /sup 16/O(/sup 6/Li, ..cap alpha..)/sup 18/F reaction to the 1/sup +/ (0.0 MeV), 3/sup +/ (0.937 MeV), and 0/sup -/ + 5/sup +/ (1.1 MeV) states in /sup 18/F at a bombarding energy of 34 MeV. In addition, forward angle data have been measured for the 2/sup -/ (2.101 MeV), 1/sup +/ (3.725 MeV), 3/sup -/ (3.791 MeV), and 2/sup +/ (3.836 MeV) states. The angular distributions for all of the above states are forward peaked and have little structure at back angles. The general structure of the first 60/sup 0/ of the angular distributions can be reproduced by zero-range two-particle transfer distorted-wave Born-approximation calculations; however, the calculations are generally 3/sup 0/ and as much as 10degree out of phase with the data past the first maximum. A zero-range distorted-wave Born-approximation normalization factor of 100 is obtained assuming the 5/sup +/ state to be a pure (d/sub 5;2/)/sup 2/ configuration. Finite-range distorted-wave Born-approximation calculations which include the 2S and 1D components of /sup 6/Li do not improve the fits to the data and are similar to zero-range calculations at forward angles. The 1Dmore » component was shown to have little effect on the calculated angular distributions. The absolute magnitudes of the cross sections are predicted to within a factor of 2 when the /sup 18/F shell model wave functions of Kuo and Brown are used in the finite-range distorted-wave Born-approximation calculations. Two-particle and cluster form factors used in the finite-range calculations gave equivalent fits to the data. The magnitude of the cross section at angles greater than 90/sup 0/ and the phase of the forward angle data could not be reproduced by any of the calculations. The failure of the distorted-wave Born-approximation calculations at back angles suggests that a more complete description of the reaction mechanism which includes the exchange of an ..cap alpha.. particle in /sup 16/O with the /sup 6/Li projectile is necessary. (AIP)« less