Orateur
Description
Among challenging problems in physics is the understanding of emergent collective excitation modes in interacting quantum many-body systems in terms of the microscopic degrees of freedom. The study of evolution of properties of the nucleus, as function of excitation energy, angular momentum and isospin open avenues to search for simple patterns to identify and better understand hidden aspects of the nucleus.
Among various phenomenon, nuclei can also vibrate in surprisingly ordered ways. Vibrations that have played a central role in revealing nature’s fundamental laws, can be explored starting from things as simple as a pendulum to more complex gravitational waves. In nuclei phonons represent quantized collective excitations. Multiphoton states occur when two or more phonon are excited. The study of multi-phonon excitations opens a window into the collective dynamics of many-body systems, whether they be atoms in a solid or nucleons in a nucleus. The investigations and the evolution of the structure moving away from stability and the study of difficult to study odd-odd nucleus, where orderly collective motion is usually hidden by chaotic individual particle behaviour, could help to better understand the driving force of valence neutrons and protons and the dynamical behaviour of surface vibrations. The Nb isotopic chain is an ideal laboratory for these investigations.
The structural evolution of the neutron-rich Nb isotopes were probed as a function of spin and isospin using prompt and delayed discrete gamma-rays from isotopically identified nuclei. The neutron-rich Nb isotopes studied here were produced as fission fragments in reactions with a 238U beam at 6.2 MeV/u on a 9Be target at GANIL. The spectrometer (VAMOS++) coupled to a γ-ray tracking array AGATA along with the EXOGAM array, were used to identify the excited states of the fission fragments. These measurements were combined with independently obtained high-fold γ-ray coincidence measurements employing a 252Cf source at Gammasphere array (when at LBL, USA). These powerful complementary techniques allowed the characterization of the Nb isotopic chain till the very neutron-rich nucleus, 109Nb.
In this talk, after a brief introduction we will present results of these measurements, including calculations, to probe the evolution of structure of these isotopes very far from the valley of stability and demonstrate the first evidence illustrating the robustness of 2-phonon vibrational excitations in the presence of both an odd valence proton and neutron as well as the possibility of coexisting shapes beyond the N=60 transitional region.