RIBF ULIC and CNS Symposium on Frontier of Gamma-ray Spectroscopy (Gamma11)

Search for Jacobi shape transition in hot rotating 88Mo nuclei through Giant Dipole Resonance decay

1 Jul 2011, 11:00

20m

RIBF conference room

Exotic deformation / new collective motion at low and high spin

Speaker

Mr Michal Ciemala (Institute of Nuclear Physics PAN, Poland)

Description

The study of the properties of the giant dipole resonance (GDR) at high temperature and angular momentum is one of the central topics in nuclear structure as it provides insight into the behavior of nuclei under extreme conditions. The wealth of experimental data on this subject covers in most cases an interval of temperatures up to 2.5 MeV and is mainly based on the study of the GDR gamma-decay from fusion-evaporation reactions. These data have been shown to provide evidence of relevant physical effects such as damping and shapes, the latter in the liquid drop regime. Of special interest are shape changes induced by temperature and angular momentum, particularly the predicted Jacobi shape transition, seen up to mass 50 and to be confirmed by exclusive experimental data also in heavier nuclei. This phenomenon is predicted as an abrupt change from an oblate to a more elongated triaxial shape occurring at the so called critical value of spin above which the nucleus undergoes scission. An experiment focussing on the 88Mo nucleus was performed in LNL Legnaro using 48Ti beam at 300, 450 and 600 MeV on 40Ca target and producing by fusion evaporation compound nuclei at temperatures of 3, 3.8 and 4.5 MeV. High-energy gamma-rays were measured in coincidence with residues and alpha particles and the data were analysed with the statistical model (CASCADE). The data have allowed to extract the spin and temperature evolution of the GDR width in 88Mo up to at high temperature values, region where information are scarce. A change of the GDR width with angular momentum and temperature was found and this reflects the role played by quantal and thermal fluctuations in the damping of the giant vibrations. In addition, preliminary results deduced from the fit of the measured GDR line-shapes seem to suggest existence of Jacobi shape transition in 88Mo. Future possibilities of similar studies in more exotic nuclei will be discussed in the context of soon available radioactive beam facilities, as e.g. SPIRAL2. Especially the role of a novel detector PARIS in such investigation will be shown.