Scissors Mode in Gd Nuclei

Spectra of gamma rays following neutron capture at isolated resonances of 6 stable Gd isotopes were measured with highly segmented BaF2 detector DANCE at the Los Alamos LANSCE spallation neutron source. The main emphasis was put on studying the gamma-cascade decay of neutron resonances to get unique information on photon strength. An analysis of the accumulated gamma-ray spectra within the extreme statistical model leads to an inescapable conclusion that scissors mode resonances are built not only on the groundstate, but also on excited levels in all product nuclei studied. The results on summed B(M1)up arrow strength and energy of the scissors mode are compared with systematics of scissors mode parameters for the ground-state transitions deduced from nuclear resonance fluorescence measurements. A specific feature of our experiments is the investigation of scissors mode of odd nuclei, for which the nuclear resonance fluorescence provides only limited information.