γ-spectroscopic determination of mean lifetimes and magnetic moments of excited nuclear states

Abstract

The mean lifetime of an excited nuclear state is an important observable directly related to the transition probability. Information on the mean lifetimes of nuclear excited states can give insight into the evolution of the nuclear shape as a function of nucleon number. For this work, mean lifetimes of the rare-earth isotopes 174,176,178,180Hf and 152Gd have been measured. The mean lifetimes have been determined with the fast-timing technique, already introduced in the 1950s, but applicable to a wider range of excited nuclear states, due to rapid progress in the development of new scintillation detectors in the last two decades. Both experiments have been performed at the FN Tandem accelerator of the IFIN-HH with the ROSPHERE detector array. A possible new signature for the known quantum phase transition at N=90 has been established with the results from the 152Gd experiment and the correlation to other observables, such as the E0 transition strength, has been investigated. The evolution of collectivity and the rotational structure of the hafnium isotopes have been investigated and a maximum of the collectivity at N=100 has been identified. In total 13 mean lifetimes have been determined for the 174,176,178,180Hf isotopes. The nuclear magnetic dipole moment is an important indicator of the composition of the proton neutron wave function, and therefore the single particle properties of the nuclear state. The second part of this thesis presents the results from a g-factor measurement of the 2+1 state of 18O with the recently developed ECR-TDRIV technique. The method is in particular foreseen for the application to radioactive ion beams, but has to be tested with stable beams. The analysis procedure of the 18O experiment is outlined and the results for the g factor are compared to previous measurements and shell model calculations.