In-Beam spectroscopy of extremely neutron deficient nuclei [sup 110]Xe [sup 163]Ta [sup 169]Ir and [sup 172]Hg

Abstract

This thesis describes new results obtained from experimental studies of the extremely neutron-deficient isotopes 110Xe, 163Ta, 169Ir, and 172Hg, close to the proton drip-line. The experiments used state-of-the-art equipment for nuclear spectroscopy where a large highresolution Germanium-detector array was coupled to a high-transmission recoil separator. The highly selective recoil-decay tagging technique was applied in order to identify and study the most weakly populated reaction channels. The work is based on four experiments performed at the Accelerator Laboratory of the University of Jyväskylä, Finland. The experimental techniques used and the experimental set-ups are described. Comparison between experimental results and theoretical predictions are made. The thesis also briefly summarises the theoretical models employed to interpret the experimental data. The results for 110Xe indicate an emergence of enhanced collectivity near the N=Z line in the region of the nuclear chart above 100Sn. These findings are interpreted as a possible effect of increased neutron-proton isoscalar pair correlations, a residual interaction effect not accounted for in present-day nuclear models. The findings for 163Ta reveal three strongly coupled band structures built on different quasiparticle configurations. The low-lying yrast band exhibits strong signature splitting indicative of a significant triaxial shape asymmetry. An intriguing possibility exits for enhanced octupole correlation in 163Ta, where the odd-proton is proposed to couple to an octupole-vibrational phonon. However, further investigations are needed to elucidate this scenario. Also for 169Ir do the properties of the yrast structure point to a rotational-like behaviour of a moderately deformed nucleus exhibiting a triaxial shape. For neither 163Ta or 169Ir do the experimental results fully agree with theoretical predictions for the shape evolution of the neutron-deficient tantalum and iridium isotopes, approaching the proton drip-line. The nearly constant level spacing in 172Hg between the lowest excited 2+, 4+ and 6+ states suggests a transition to a near-spherical harmonic collective vibrational structure as compared with heavier even-even Hg isotopes around the neutron midshell and above. The experimental data have been compared with total Routhian surface calculations and quasiparticle random phase approximation calculations.