Photon strength functions in Gd isotopes studied from radiative capture of resonance neutrons

¹ Charles University in Prague, CZ-180 00 Prague 8, Czech Republic
² North Carolina State University, Raleigh, North Carolina 27695, USA and Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA
³ MonAme Scientific Research Center, P.O.Box 24-603, Ulaanbaatar, Mongolia
⁴ Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, New Mexico 87545, USA
⁵ Lawrence Livermore National Laboratory, Livermore, California 94551, USA

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

Published online: 1 April 2014

Abstract

The experimental spectra of γ rays following radiative neutron capture on isolated resonances of stable ^{152,154–158}Gd targets were measured by the DANCE calorimeter installed at the Los Alamos Neutron Scattering Center in New Mexico, USA. These spectra were analyzed within the extreme statistical model to get new information on the photon strength functions. Special emphasis was put on study of the scissors vibrational mode present in these isotopes. Our data show that the scissors-mode resonances are built not only on the ground states but also on the excited levels of all studied Gd isotopes. The scissors mode strength observed in ^157,159Gd products is significantly higher than in neighboring even-even nuclei ^156,158Gd. Such a difference indicates the existence of an odd-even effect in the scissors mode strength. Moreover, there exists no universal parameter-free model of the electric dipole photon strength function describing the experimental data in all of the Gd isotopes studied. The results for the scissors mode are compared with the (γ, γ′) data for the ground-state transitions and with the results from ³He-induced reactions.