J.F. Smith

Single particle excitations and properties of multiple band terminations near spin 50ħ in 158Er

The competition between collective rotation and single-particle behaviour at high spin in 158Er has been investigated with the Eurogam spectrometer. Band terminating states have been observed in three structures at Iπ = 46+, 48− and 49− and specific single-particle configurations are assigned by comparison with cranked Nilsson-Strutinsky calculations. These special states are found to be related by very simple single particle excitations. These data indicate that an oblate mean field (ϵ ∼ −0.14) is established for a nuclear core plus 12 aligned valence nucleons which is stable against single-particle rearrangements. In the (π, α) = (+, 0) states the collective and weakly collective terminating structures are observed to coexist between 30+ and 46+.

Multi-nucleon transfer reactions as a tool for spectroscopy of heavy nuclei

Multi-nucleon transfer reactions have been shown to be an important tool for high-spin spectroscopic studies of Rn, Ra and Th nuclei with N 134. These nuclei have been populated using the heavy-ion collisions of 56 Fe+ 232 Th, 86 Kr+ 232 Th and 136 Xe+ 232 Th at beam energies 15-20% above the Coulomb barrier. Excited states with spins as high as 28 have been observed using the latter reaction. Yield distributions of binary-reaction products stopped in thick targets have been derived from the analysis of - and - - coincidence events. These yields indicate that there is significant fission of the target-like reaction products. Intensities deduced for products resulting from neutron transfer or proton transfer appear to be Q -value dependent, while processes involving transfers of several protons and neutrons are governed by mass and charge equilibration.

HIGH-SPIN ISOMERS IN NEUTRON-RICH NUCLEI STUDIED WITH THE TARDIS-ARRAY AT IGISOL

Abstract A 12 Compton-suppressed detector array TARDIS has been placed around the collection spot of the IGISOL separator, with the aim of studying decays of high-spin isomers in neutron-rich isotopes produced by fission. An experiment on 97 Y shows that the detection limit is improved by more than one order of magnitude with respect to previous measurements at research reactors with conventional detector setups.

Band termination spectroscopy in 157Er

The level scheme of 157Er has been extended from a spin region where the nucleus behaves as a prolate rotor to a region where the spin is produced by the alignment of all or most of the available valence nucleons along the symmetry axis of a weakly deformed oblate shape. The level scheme was established at high spin using up to four-fold gamma -ray coincidences detected in the Eurogam spectrometer following the reaction 114Cd(48Ca,5n)157Er at a bombarding energy of 210 MeV. Particularly favoured states have been established at IK=69/2+, 81/2+, 71/2+, 77/2-, 87-/2 and 89-/2. Specific single-particle configurations are assigned to these special states by comparison with cranked Nilsson-Strutinsky calculations. These states are related to structures observed in the neighbouring nuclei 158Er and 157Ho. These data provide the spectrum of single-particle states for the lowest lying valence orbitals above the 146Gd closed core.