LEVEL STRUCTURE OF OS-191 - COEXISTING OBLATE AND PROLATE CONFIGURATIONS

An extensive level scheme for the transitional nucleus Os-191 has been constructed on the basis of (n, gamma), n, e-) and (d, t) reaction data. gamma-rays following thermal capture and average resonance capture (ARC) were detected with pair spectrometers. Secondary gamma-ray spectra were obtained with the GAMS bent crystal spectrometers. The high precision of the resultant energies was the critical factor in developing a level scheme on the basis of Ritz combinations. gamma-gamma coincidences were obtained from both primary and secondary transitions. Conversion electrons, detected with the BILL spectrometer, gave multipolarity information. The (d, t) reaction measured with a Q3D magnetic spectrometer gave additional information on the hole states in Os-191. A discussion of the resulting level scheme briefly reviews the fragmentation of negative-parity strength but focuses mostly on a rare example of an anti-aligned decoupled set of coexisting positive-parity states. For these, triaxial particle-plus-rotor calculations are carried out. Reasonable agreement is obtained and the calculations also explain the unusually strong population in (n, gamma) of this set of mostly medium spin states.