Studies of excited states in the odd-odd nucleus 178Au

Atomic nuclei close to the Z = 82 shell closure are well known for exhibiting shape coexistence with one of the earliest examples of this being the neutron-deficient gold (Z = 79) nuclei close to the neutron mid shell gap at N=104. Subsequently, such isotopes have been examined with both laser-spectroscopy and decay studies. The present investigation was motivated by the recent experiments at ISOLDE CERN to study the chain of gold isotopes 176−181 Au. In the odd-odd nucleus, 178 Au (N=99), two α-decaying states were identified, a low spin (I π = 2+ , 3− ) ground state 178 Aug , and a high-spin (I π = 7+ , 8− ) isomer. Laser-spectroscopy measurements have shown both isomers to be deformed with the high-spin state having slightly larger deformation. In this thesis, excited states of 178 Au (Z=79, N=99) have been established for the first time by means of in-beam γ-ray spectroscopy. The previously established sub-microsecond isomers with half-lives of 294-ns and 373-ns were confirmed and their decay schemes to the α-decaying states of 178 Au were established with new multipolarity assignments. The existence of sub-microsecond isomers of 178 Au allowed for isomer decay tagging to be utilised to identify excited states. A total of 3 rotational bands were established. Configuration assignments of these bands has been made on the basis of comparison with similar bands in neighbouring odd-odd Ir isotopes, with the πi13/2 ⊗ νi11/2 and πh11/2 ⊗ ν f7/2 bands observed in 178 Au. The establishment of rotational bands is discussed and may also constrain the the spin-parity of both previously established α-decaying states 178 Aug,m .