High resolution study of isovector negative parity states in the O16(He3,t)F16 reaction at 140 MeV/nucleon

The isovector transitions from the ground state (g.s.) of O16 to the negative parity states in F16, i.e., the Jπ=0- g.s., the 0.193 MeV, 1- state, the 0.424 MeV, 2- state, the 0.721 MeV, 3- state, and the 4- "stretched" state at 6.372 MeV, were studied by using a high resolution O16(He3,t)F16 reaction at 140 MeV/nucleon. With the help of high energy resolution, these states were, for the first time, clearly resolved in a charge exchange reaction at an intermediate energy, which favorably excites spin-flip states. Angular distributions of the reaction cross sections were measured in the laboratory frame from 0° to 14°. Parameters of phenomenological effective interactions were derived so as to reproduce these angular distributions in distorted wave Born approximation (DWBA) calculations. The angular distribution of the 0- state could be reproduced well at θc.m.<10°. The empirical values, however, are larger by a factor of 2-2.5 in the larger angle region, where the contribution of the so-called "condensed pion field" is expected. The high resolution also enabled the decay widths of these states to be measured.