The region surrounding the Z = 82 major-shell closure has exhibited the strongest known manifestation of shape coexistence, to date. Due to this, the nuclides that inhabit this region have been subject to extensive decay- and laser-spectroscopy studies. In this work, the results from two investigations performed at the CERN, ISOLDE facility will be presented: the first, an α-decay study of two states in 178 Au, and the second, an in-source laser-spectroscopy experiment performed on a long chain of At isotopes.
Two states, a low-spin ground state, and a high-spin isomer, were directly identified in 178 Au (Z = 79, N = 99) for the first time. Due to the highly selective resonant laser-ionisation method, it was possible to produce isomerically pure beams of the ground and isomeric states. These beams were then ustilised in order to perform dedicated α-decay studies upon the two states. Successful measurements were made for the half-lives, branching ratios, and decay patterns of 178g,mAu.
The first ever laser-spectroscopy measurements were performed on a long chain of At isotopes, using the in-source resonant ionisation technique. The isotope shifts and hyperfine structures of long-lived states in 195−211,217−219At were measured. From these, values for the corresponding changes in mean-squared charge radius, and magnetic dipole moments were extracted. The charge-radii of the neutron-deficient At isotopes display a strong onset of deformation, as the neutron number approaches the N = 104 midshell. The observed onset is more pronounced than the one seen in the Po isotopes, which is noted to be exceptionally strong. Based on the extracted charge-radii and magnetic moments, cases for shape coexistence were identified in 195,197,199At. In the case of the neutron-rich At isotopes, an inversion of the normal odd-even-staggering has given evidence for the presence of octupole collectivity.
