W. F. Piel

Very-high-spin and core-coupled states in 213Rn. a test of the applicability of the deformed independent particle model

Excited states in 212,213Rn were populated in the bombardment of 204Hg by 14C ions of energies 80-94 MeV. The depopulation of the excited states was studied using in-beam spectroscopic methods including γ-ray excitation, γ-ray angular distribution, γ-γ-t coincidence, pulsed-beam-γ timing and conversion electron measurements. Spins up to Jπ = 30 and a tentative J = (73/2) were observed, respectively. In 212Rn the previous level scheme was confirmed, with the addition of five new transitions of which one feeds the 30+ state. In 213Rn the previously reported level scheme was mainly confirmed and it was extended to (71/2) or (73/2), which is the highest spin observed to-date in a lead-region nucleus. Several transition rates B(λ) were deduced from isomeric half-lives or branching ratios in both isotopes. Deformed Independent Particle Model (DIPM) calculations were performed to assign configurations, which in 213Rn usually consist of the odd neutrons vg9/2 and vj15/2 coupled to the four-proton states in 212Rn. The highest levels include neutron core-excitations, since the maximum valence-nucleon angular momentum in 213Rn is 55/2. The very topmost levels even need 2- particle-two-hole excitations. Shape changes in these two Rn isotopes are discussed, as are the transition rates.

High-Spin Properties of Doubly-Odd Nuclei of Mass ≈130

Light rare-earth nuclei of mass A ≈ 130 are predicted to possess relatively flat potential-energy surfaces with respect to γ, the asymmetry parameter in the polar representation of rotating quadrupole shapes. Because of this γ softness, valence nucleons in high-j orbitals can greatly modify the nuclear shape. Whereas protons from the bottom of the h 11/2 subshell maintain the nuclear core near the collective prolate shape, γ = 0°, valence neutrons from the top of the h 11/2 subshell drive the nuclear core towards the collective oblate shape, γ = 60°. Such competition between the shape-driving forces of the valence nucleons makes the study of doubly-odd nuclei most interesting. Triaxial yrast bands built on the πh 11/2 ⊗ vh 11/2 configuration have systematically been observed in isotopes ranging from Cs to Eu (55 ≤ Z ≤ 63). The characteristic features of these bands will be discussed and their properties compared to theoretical expectations.