Search

The population of metastable states produced in relativistic-energy fragmentation of a U-238 beam has been measured. For states with angular momentum greater than or similar to 20h, a much higher population than expected has been observed. By introducing a collective component to the generation of angular momentum the experimental data can be understood. This is the first time that a collective degree of freedom has be shown to play a major role in such high-energy collisions. (c) 2005 Elsevier B.V. All rights reserved.

The 3/2- isomer in 185Pb and states above it have been populated in the α-decay of 189Po. The observed α-decay strengths to and the electromagnetic decay properties of the excited states in 185Pb have been combined with Potential Energy Surface and Particle-Plus-Rotor calculations to propose configuration assignments. It is suggested that the α-decaying isomer of 189Po is of prolate origin and that the prolate configuration becomes very low in energy in 185Pb.

Detailed fine-structure $\alpha$ -decay studies of 188,190Bi were performed using the complete-fusion reactions of 50,52Cr ions with a 142Nd target at the velocity filter SHIP. The evaporation residues were separated in-flight and subsequently identified on the basis of recoil- $\alpha$ , recoil- $\alpha$ - $\gamma$ /X-ray and excitation function measurements. Improved data on the $\alpha$ -decay of 188,190Bi were obtained and a number of new low-lying excited states in the daughters 184,186Tl were observed. An intruder, presumably 10- state was identified in 184Tl, extending the systematics of such states in the odd-odd Tl nuclei beyond the neutron mid-shell at N = 104. Some technical aspects of experiment at recoil separators are also discussed.

The population of metastable states produced in relativistic‐energy fragmentation of a 238U beam has been measured. For states with high angular momentum, I=17ℏ and I=21.5ℏ, a higher population than expected has been observed, with the discrepancy increasing with angular momentum. By considering two sources for the angular momentum, related to single‐particle and collective motions, a much improved description of the experimental results can be obtained. In addition, new results on the structure of 208Fr, 211Ra and 216Ac are reported.

A systematic study of the population probabilities of nanosecond and microsecond isomers produced following the projectile fragmentation of U-238 at 750 MeV/nucleon has been undertaken at the SIS/FRS facility at GSI. Approximately 15 isomeric states in neutron-deficient nuclei around A similar to 190 were identified and the corresponding. isomeric ratios determined. The results are compared with a model based on the statistical abrasion-ablation description of relativistic fragmentation and simple assumptions concerning gamma cascades in the final nucleus (sharp cutoff). This model represents an upper limit for the population of isomeric states in relativistic projectile fragmentation. When the decay properties of the states above the isomer are taken into account, as opposed to the sharp cutoff approximation, a good agreement between the experimental and calculated angular momentum population is obtained.

High spin states in the $^{177}\mathrm{Hg}$ nucleus were populated by the $^{144}\mathrm{Sm}(^{36}\mathrm{Ar},3\mathrm{n})^{177}\mathrm{Hg}$ reaction at a beam energy of $178\phantom{\rule{0.3em}{0ex}}\text{MeV}$. The emitted prompt $\ensuremath{\gamma}$ rays were detected with the Jurosphere $\ensuremath{\gamma}$-ray spectrometer, while the recoiling nuclei were identified using an active stopper at the focal plane of the gas-filled separator RITU. A quasi-rotational band that decays to an isomeric state with a half-life ${t}_{1∕2}=1.50\ifmmode\pm\else\textpm\fi{}0.15\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{s}$ and its subsequent $\ensuremath{\gamma}$ decay to the ground state of $^{177}\mathrm{Hg}$ have been observed for the first time. Based on the observed decays from this isomeric state, we suggest that the spin of the ground state of $^{177}\mathrm{Hg}$ is ${J}^{\ensuremath{\pi}}=7∕{2}^{\ensuremath{-}}$. In addition, a sequence of transitions that bypass this isomeric state has also been observed. Evidence for shape coexistence is presented. The properties of the observed states are discussed in terms of the systematics of the mercury nuclei in this transitional region.