β-Decay properties in the vicinity of 78Ni and their implications on nuclear shell structure far off the b-stability line

by Dr Zhengyu Xu (RNC / U. Hong Kong)

Friday 30 May 2014, 13:30 → 15:00 Asia/Tokyo

RIBF Hall

The neutron-rich nuclide 7828Ni50 is of remarkable interest because of its unverified doubly magic character. The concept of nuclear magicity has been proposed since the discovery of particularly stable nuclei with specific numbers, so-called magic number, of proton and neutron, such as 2, 8, 20, 28, 50, 82, and 126. These numbers were recognized as a consequence of nuclear shell structure and interpreted by a strong spin-orbit interaction coupled with a mean field potential in the nuclei along the -stability line. Recent experimental studies, however, revealed a drastic change in the shell structure far off the  stability driven by the unique nucleon-nucleon interactions under unbalanced neutron-to-proton ratio. For instance, classical magic numbers in 12Be (N = 8), 32Mg (N = 20), and 42Si (N = 28) were found to disappear whereas new magic numbers emerged in 24O (N = 16) and 54Ca (N = 34). To address the shell evolution around 78Ni, an experiment based on decay spectroscopy was performed at the RIBF facility as part of an EURICA campaign at the end of 2012. Half-lives of 38 neutron-rich nuclei were measured including 12 new half-lives for the nuclei 73,74Fe, 76,77Co, 79,80Ni, 81,82Cu, 84Zn, 87Ga, and 87,88Ge. New -delayed neutron-emission probabilities (Pn) were also measured for the nuclei 78Ni, and 80,81Cu. Based on the new experimental results, shell evolution and magicities of Z = 28 and N = 50 were investigated in the vicinity of 78Ni.