Orateur
Description
Nuclear shapes determine the landscape of super-heavy nuclei. If it were not for shell corrections, heavy nuclei with Z$\gtrsim$104 would fission instantaneously. Deformation increases the shell corrections and enhances the stability of heavy nuclei. The evolution of deformation along the fission path determines the height of the fission barrier and its width, thereby influencing fission lifetimes. As a result, a peninsula of deformed nuclei extends from the heaviest spherical doubly magic nucleus $^{208}$Pb, towards the elusive island of super-heavy nuclei. The exact location of this island and magic numbers associated with it remain a matter of intense debate.
Trans-fermium nuclei near the Z=100, N=152 deformed shells are prolate deformed but higher order shapes play an important role for their structure. The hexacontetrapole deformation, $\beta_6$, is believed to be responsible for opening the N=152 energy gap. Studies of trans-fermium nuclei provide a stringent test of nuclear models which are used to describe the heaviest known nuclei. During the talk, recent decay spectroscopy and in-beam $\gamma$-ray spectroscopy experiments in this region using Argonne Gas-Filled Analyzer in stand-alone mode or coupled to Gammasphere will be reviewed. Among others, the observation of the ground-state rotational band in the most fissile nucleus known, $^{250}$No, the study of fast isomers in neutron-deficient Lr isotopes and the search for the rapidly fissioning nucleus, $^{252}$Rf, will be presented. These results will be compared with predictions of existing nuclear models and their impact on the shape evolution in trans-fermium nuclei will be discussed.
This material is based upon work supported by the U.S Department of Energy, Office of Science, Office of Nuclear Physics, under contract number DE-AC02-06CH11357. This research used resources of ANL's ATLAS facility, which is a DOE Office of Science User Facility.
