In-Beam Spectroscopy of Extremely Neutron Deficient Nuclei 110Xe, 163Ta, 169Ir and 172Hg

University dissertation from Stockholm : KTH

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 high resolution Germanium-detector array was coupled to a high-transmission recoil separator.The highly selective recoil-decay tagging technique was applied in order to identify andstudy the most weakly populated reaction channels. The work is based on four experimentsperformed at the Accelerator Laboratory of the University of Jyväskylä, Finland. The experimental techniques used and the experimental set-ups are described. Comparisonbetween experimental results and theoretical predictions are made. The thesis also brieflysummarises the theoretical models employed to interpret the experimental data.The results for 110Xe indicate an emergence of enhanced collectivity near the N=Z linein 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 differentquasiparticle configurations. The low-lying yrast band exhibits strong signature splittingindicative of a significant triaxial shape asymmetry. An intriguing possibility exits forenhanced octupole correlation in 163Ta, where the odd-proton is proposed to couple to anoctupole-vibrational phonon. However, further investigations are needed to elucidate thisscenario.Also for 169Ir do the properties of the yrast structure point to a rotational-like behaviourof a moderately deformed nucleus exhibiting a triaxial shape. For neither 163Taor 169Ir do the experimental results fully agree with theoretical predictions for the shapeevolution of the neutron-deficient tantalum and iridium isotopes, approaching the protondrip-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 structureas 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.