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The domain of nuclei situated far from the line of b stability has always been an arena of numerous experimental pursuits and a testing ground for new theoretical models. With radioactive beams on the horizon, the physics of nuclei with an excess of neutrons or protons has become one of the focal points of nuclear physics. These nuclei define the very limits of nuclear existence and will be susceptible to phenomena associated with low binding energy, such as halos, skins, or mixing between bound and continuum states. The proton separation energy decreases with decreasing neutron number. Proton-rich nuclei, which have a negative proton separation energy and are, thus, situated beyond the proton drip-line, can spontaneously emit protons. The proton decay rate is governed by the energy and orbital angular momentum of the emitted proton. It also depends on the wave function of the proton-decaying state, which is determined by the shape of the nuclear potential and by residual interactions between valence nucleons. Most of the known proton emitters have decay rates consistent with the assumption of a spherical potential. The recent experimental

The entry distribution in angular momentum and excitation energy for the formation of {sup 254}No has been measured after the {sup 208}Pb( {sup 48}Ca, 2 n) reaction at 215 and 219 MeV. This nucleus is populated up to spin 22({Dirac_h}/2{pi}) and excitation energy (greater-or-similar sign)6 MeV above the yrast line, with the half-maximum points of the energy distributions at {approx}5 MeV for spins between 12({Dirac_h}/2{pi}) and 22({Dirac_h}/2{pi}) . This suggests that the fission barrier is (greater-or-similar sign)5 MeV and that the shell-correction energy persists to high spin. (c) 2000 The American Physical Society.

The ground-state band of the Z=102 isotope {sup 254}No has been identified up to spin 14, indicating that the nucleus is deformed. The deduced quadrupole deformation, {beta}=0.27 , is in agreement with theoretical predictions. These observations confirm that the shell-correction energy responsible for the stability of transfermium nuclei is partly derived from deformation. The survival of {sup 254}No up to spin 14 means that its fission barrier persists at least up to that spin. {copyright} {ital 1999} {ital The American Physical Society }