Complex alignment mechanism and lifetimes of high spin states in ¹⁷²Os and ¹⁷³Os

Abstract

High spin states in 172Os and 173Os have been investigated by γ - γ coincidence studies. States were populated by the 144Nd(32S, 4n/3n) reactions using 162-MeV 32S ions from the HHIRF tandem accelerator at ORNL. For the spectroscopy study, measurements were made with the Oak Ridge Compton Suppression Spectrometer System incorporated into the Spin Spectrometer. The yrast band in 172Os was observed up through the 30+ state and four new side bands were deduced. A band identified as belonging to the previously unknown 173Os was also observed. Results were interpreted using average nuclear field calculations which incorporated the deformed Woods-Saxon potential with its "universal" parameterization, a cranking approximation and the Hartree-Fock-Bogolyubov method. A semiquantitative agreement with experiment to explain e.g. the low-frequency anomaly seen in 172Os was obtained. Lifetimes of high spin states in 172Os were measured by the recoil distance technique. The γ - γ coincidences at 20 different target-stopper distances were recorded between six germanium detectors at 90° to the beam direction and a Compton-suppressed Ge detector at 0° to record the shifted and unshifted γ-ray peaks. Coincidences allowed the use of versatile gating procedures in the analysis. The extracted lifetimes and quadrupole moments were found to support the conclusions based on the spectroscopical and theoretical studies.