Triaxiality in neutron-rich Ruthenium isotopes, New lifetimes measured in Ru-109,110,111

Abstract

This thesis explores the asymmetrical deformation of Ruthenium isotopes, aiming to provide reliable experimental data useful for testing theoretical nuclear structure models. We have obtained reduced transition probabilities B(E2) for a number of transitions in Ru-109,110,111. A fit of the generalised triaxial rotor model indicates Ru-110 is well deformed, with a slightly oblate triaxial shape. The results are compared to various global nuclear structure models. First approximation reveals no evidence of shape changes between Ru-109 and Ru-111, more accurate results will be achieved through triaxial particle rotor calculations. The dataset at the heart of the analysis, obtained with AGATA and VAMOS++ at GANIL in 2017, features much higher statistics for a much larger number of nuclei than have previously been available. This has allowed us to get reliable lifetime measurements for the neutron odd Ru-109,111, and for both the ground- state band and one phonon γ-band in Ru-110. Additionally, it is expected to significantly reduce systematic errors when comparing results from different nuclei. We have developed and applied a new method for extracting lifetimes from the decay curves obtained in recoil distance Doppler shift measurements. By imposing constraints of physicality, it is expected to produce more reliable results than previous methods. A code for simultaneously fitting multiple gamma-spectra with shared parameters has also been developed.