Scissors Mode in Gd Nuclei

¹ Charles University in Prague, CZ-180 00 Prague 8, Czech Republic
² North Carolina State University, Raleigh, NC 27695 and Triangle Universities Nuclear Laboratory, Durham, NC 27708
³ Lawrence Livermore National Laboratory, Livermore, CA 94551
⁴ Los Alamos National Laboratory, Los Alamos, New Mexico 87545

^a e-mail: kroll@ipnp.troja.mff.cuni.cz

Abstract

Spectra of γ 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 γ-cascade decay of neutron resonances to get unique information on photon strength. An analysis of the accumulated γ-ray spectra within the extreme statistical model leads to an inescapable conclusion that scissors mode resonances are built not only on the ground-state, but also on excited levels in all product nuclei studied. The results on summed B(M1)↑ 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.