Excitation of isovector states by the ( 7Li, 7Be) reaction on 12C and 13C

Abstract

Isovector states in 12B and 13B are studied by using the ( 7Li, 7Be) reaction at a projectile energy of 21 MeV/nucleon. Angular distributions are measured at forward scattering angles of θ L ⩽ 10° and compared with one-step distorted-wave Born approximation (DWBA) calculations. The form factors are microscopically evaluated with effective nucleon-nucleon interactions and realistic transition densities. The DWBA calculations reproduce the observed cross sections with normalization factors near to unity. This suggests that the ( 7Li, 7Be) reaction at 21 MeV/nucleon proceeds mainly through the one-step direct reaction process. The excitation of the giant dipole resonance is confirmed at E x = 7.6 MeV in 12 B and at E x = 9.5 MeV in 13B, from which the isovector collective potential strength is obtained to be V 1 ∼ 50 MeV. The isovector octupole strength is observed in three states in 12B, but it is not distinctly observed in 13B.