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

The isovectortransitions from the ground state (g.s.) of 16 O to the negative parity states in 16 F, i.e., the J π = Ο - 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 16 O( 3 He,t) 16 F 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-flipstates. 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 θ c.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.