Microscopic study of Gamow-Teller and spin-dipole states in 208Bi

Gamow-Teller (GT) and spin-dipole (SD) states in 208Bi are studied by using self-consistent Hartree-Fock + Tamm-Dancoff approximation taking into account the coupling to the continuum. Most of SD strength is found at the excitation energy Ex≈ 25MeV with a very broad width, which agrees with recent experimental observations. It is shown that Landau damping effect is responsible for the large width of SD peak, while the escape width is found to be at most 1MeV. We study also electric dipole (E1) transitions between GT and SD states in 208Bi. Main E1 transitions for 0- and 1- states are found near excitation energy expected from Brink's hypothesis in which SD states are considered as E1 resonances built on the GT state. Calculated E1 transition strengths between GT and SD states are compared with the analytic sum rules within one-particle one-hole (1p-1h) configuration space and within both 1p-1h and 2p-2h model space.