Nuclear rotation at the fission limit in
Résumé
A ground-state rotational band in the fissile nucleus was observed for the first time. Levels up to spin and excitation energy of 1.56 MeV were observed. The nuclei were produced using the fusion-evaporation reaction. It is the weakest reaction channel ever studied using in-beam -ray spectroscopic methods. The reaction products were separated from the beam in the Argonne gas-filled analyzer (AGFA). The nuclei were implanted into a double-sided Si strip detector at the AGFA focal plane and tagged with subsequent ground-state spontaneous fission decays using temporal and spatial correlations. Prompt rays in coincidence with the recoils were detected in the Gammasphere array of Ge detectors. In order to identify the ground-state rotational band in , a method for identifying rotational bands in low statistics -ray spectra was developed. The deduced kinematic moment of inertia is smaller compared to neighboring even-even nuclei. This is most likely associated with a slightly lower quadrupole deformation and stronger pairing correlations in . The behavior of the moment of inertia as a function of rotational frequency is similar to that of the lighter isotones and .