The Coupling of the Spin-Dipole Mode with the Dipole Oscillations

The coupling of the spin-flip dipole mode with the dipole oscillation is studied through the analysis of photoabsorption cross sections in light nuclei and also El radiative widths from isobaric analog states in heavy ones. It is shown that this coupling is reasonably under stood by the central force and the tensor force, where the latter works additively to the former. The role of the two-body spin-orbit force has only a minor role for this coupling, for the main coupling .terms of this force vanish so long as the shell model wave functions are assumed. The anomalously large El radiative width of the isobaric analog state in Bi209, which is deduced from the Bi209 (e,e'p)Pb20B reaction at Tohoku University, cannot be ex plained from our studies. However, our .results are consistent with the value obtained from the Pb208(p, ro)Bi209 reaction at the State University of New York at Stony Brook.