ORBITAL AND SPIN M1 EXCITATIONS IN ACTINIDE NUCLEI

The large variety of experimental information on M1 excitations in Th- 232 and U-236, U-238, obtained from (gamma, gamma'), (e,e') and (p,p') experiments, is described in QRPA with a deformed Woods-Saxon potenti al and separable residual interactions. The most accurate experimental data on the low-energy orbital excitations, including their (e,e') fo rm factors, are well reproduced. The influence of different parametriz ations of the spin-orbit and spin-spin forces on the spin M1 strength distribution is studied and the two maxima of this strength are interp reted as isoscalar and isovector ones. The role of the spin-independen t residual interaction for the promotion or suppression of the scissor s mode is discussed. It is found that the scissors mode fragments main ly (70%) over the low-lying orbital 1+ states and most of the stronges t experimentally observed M1 excitations can be interpreted as perform ing a weakly collective scissors motion.