New μs isomers in the neutron-rich 210 Hg nucleus

Abstract

Neutron-rich nuclei in the lead region, beyond N = 126, have been studied at the FRS-RISING setup at GSI, exploiting the fragmentation of a primary uranium beam. Two isomeric states have been identified in 210 Hg: the 8 + isomer expected from the seniority scheme in the νg 9/2 shell and a second one at low spin and low excitation energy. The decay strength of the 8 + isomer confirms the need of effective three-body forces in the case of neutron-rich lead isotopes. The other unexpected low-lying isomer has been tentatively assigned as a 3 − state, although this is in contrast with theoretical expectations. Keywords:Atomic nuclei are complex many-body systems with many degrees of freedom; nevertheless their spectral properties often show very regular features due to the symmetries of the nuclear hamiltonian. A remarkable example of this is offered by the occurrence of the seniority excitation scheme in spherical, semi-magic nuclei [1]. A deviation from this regular behaviour suggests a change in the underlying nuclear structure,

Review of metastable states in heavy nuclei

“…[123,124]) have catalogued expected deformation changes across the region. The theoretical results of Wheldon et al [125] predict a prolate but very soft potential minimum for the ground state in 190 Os (see figure 11) with a transition that develops through 192 Os and 194 Os, in which dual mimima are seen, connected through a valley in the γ direction, progressing on to a well-defined oblate minimum in the neutron-rich isotope 196 Os. Potential energy surfaces for even-even osmium isotopes, 190−196 Os, illustrating the transition between prolate and oblate shapes, from Ref.…”

β-decay studies of neutron-rich Tl, Pb, and Bi isotopes

“…This wealthy dataset has already provided some important results, such as the identification of seniority isomers along the neutron-rich Pb chain [26], the measurement of β half-lives in neutron-rich Tl and Bi isotopes [8], and the observation of new μs isomers in the neutron-rich 210 Hg nucleus [27].…”

New spectroscopic information on Tl211,213 : A changing structure beyond the N=126 shell closure

“…Preliminary studies have concerned mainly mercury isotopes, with spectroscopic studies on 208 Hg and 210 Hg conducted by means of isomer decay. While in the N = 128 208 Hg isotope a seniorityscheme-like structure is observed [1], similarly to lead isotopes [2], in 210 Hg the spectrum exhibits some differences [3]. Besides the expected I π = 8 + seniority isomer, another low-lying isomeric state appears.…”