Resolved dipole strength below the El giant resonance in Ba-138 - art. no.051307

The electromagnetic dipole response of Ba-138 was measured up to 6.7 MeV ex citation energy in a photon scattering experiment. Two Euroball Cluster det ectors were used to detect the scattered photons under 94 and 132 degrees. The Cluster at 94 degrees served as a Compton polarimeter. The total observ ed dipole cross section is in good agreement with previous tagged photon da ta, but in the present experiment the transition strength and the electric character of most of the transitions has been determined on a state-by-stat e basis. The data show a concentration of E1 strength around 6 MeV. For one of the strongest excitations M1 character is suggested. The results of mod el calculations using the quasiparticle phonon model (QPM) agree with the o bserved electric dipole strength distribution. [S0556-2813(99)51311-3].