The question of the maximum number of nucleons that can reside in a nucleus has driven a major effort in both the production and study of nuclei at the limits of mass and in their theoretical description. Contemporary models disagree on the location of the long-predicted island of stability for spherical superheavy nuclei, which remains beyond current experimental reach. Transfermium nuclei close to the Z=100, N=152 deformed shell gaps are, however, accessible experimentally, and information on their structure can provide stringent tests for existing models. In particular, the location of high-K isomers can be used to deduce single-particle energies. Two-quasiparticle (2qp) K isomers have been observed in several even-even N=150 isotones, from 244Pu to 252No. I will focus on the striking case of the very fissile nucleus 254Rf - the heaviest known N=150 isotone, in which a 2qp and 4qp isomer have been recently observed using the Argonne Fragment Mass Analyzer and the Berkeley Gas-filled Separator. Surprisingly, the decay of the 2qp isomer is four orders of magnitude faster than found for analogous isomers in lighter N=150 isotones, indicating a rapid change in nuclear structure. Also unexpectedly, no evidence was found for a fission branch from either isomer. The resulting unprecendented fission hindrance, relative to the ground-state fission, opens up the tantalizing possibility that K isomers in superheavy nuclei could live longer than their ground states.
Argonne Physics Division Seminar Schedule