No abstract

Rotational bands feeding the ground state and the isomeric state in the proton emitter 141 Ho were observed using the recoil-decay tagging method. This constitutes direct evidence that 141 Ho is deformed. A quadrupole deformation of b 2 0.25͑4͒ was deduced for the ground state from the extracted dynamic moment of inertia. Based on observed band crossings and signature splittings the 7͞2 2 ͓523͔ and 1͞2 1 ͓411͔ configurations were proposed for the ground state and the isomeric state, respectively. Comparison with particle-rotor calculations for b 2 0.25 indicates, however, that 141 Ho may have significant hexadecapole deformation and could be triaxial in the 7͞2 2 ͓523͔ ground state.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 as

The ground state rotational bands of the N = Z nuclei (72)Kr, (76)Sr, and (80)Zr have been extended into the angular momentum region where rotation alignment of particles is normally expected. By measuring the moments of inertia of these bands we have observed a consistent increase in the rotational frequency required to start pair breaking, when compared to neighboring nuclei. (72)Kr shows the most marked effect. It has been widely suggested that these "delayed alignments" arise from np-pairing correlations. However, alignment frequencies are very sensitive to shape degrees of freedom and normal pairing, so the new experimental observations are still open to interpretation.

The entry distribution in angular momentum and excitation energy for the formation of 254No has been measured after the 208Pb(48Ca,2n) reaction at 215 and 219 MeV. This nucleus is populated up to spin 22Planck's over 2pi and excitation energy greater, similar6 MeV above the yrast line, with the half-maximum points of the energy distributions at approximately 5 MeV for spins between 12Planck's over 2pi and 22Planck's over 2pi. This suggests that the fission barrier is greater, similar5 MeV and that the shell-correction energy persists to high spin.