Seminarium Fizyki Jądra Atomowego

Nuclear isomers play a key role in understanding nuclear structure physics. Of special interest are shape isomers: they may arise when the nuclear potential energy surface (PES) in the deformation space has minima associated with different shapes and when these minima are separated by a high barrier.So far, shape isomers, discovered in the 60’s, were known to occur only in the heavy actinide nuclei, although, since the 80’s, mean-field models predicted their existence also in lighter systems, pointing to 66Ni and 68Ni as the lightest candidates. Recently, also fully microscopic, state-of-the-art shell-model calculations, based on Monte Carlo computational schemes and the use of very powerful supercomputing systems, predicted shape coexistence in the neutron-rich Ni isotopes and indicated 66Ni as the best case for the existence of shape isomerism. By using high resolution gamma-ray spectroscopy and a very selective nuclear reaction mechanism, we located a shape-isomerlike structure in 66Ni [1]. Our finding shows that shape isomerism is possible not only in very heavy nuclei - it remarkably appears also in significantly lighter systems, as correctly predicted by theory, what should help to solve the puzzle on the microscopic origin of nuclear deformation.
[1] S. Leoni, B. Fornal, N. Marginean, M. Sferrazza, Y. Tsunoda et al., Phys. Rev. Lett. 118, 62502 (2017).