题目：Shell evolution from stable to neutron-rich nuclei: Structure of 30Ne (N=20) and 52Ar (N=34)
报告人：刘红娜 （CEA-Saclay IRFU / Department of Nuclear Physics ）
Shell evolution from stable to neutron-rich nuclei: Structure of 30Ne (N=20) and 52Ar (N=34) Exploring the shell evolution from stable to neutron-rich nuclei lies at the heart of nuclear structure study. In the conventional image, nuclei with magic number (2, 8, 20, 28, 50…) of protons and/or neutrons have closed shell structure and are spherical, while an increasing deformation develops towards the midshell region. Such transitions result from the competition between the shell gap and quadrupole correlations. Scientific progress in the past decades shows that shell gaps indeed can change with the number of nucleons. Quadrupole correlations can win even in a “magic” nucleus, leading to a deformed ground state. A prominent example is the existence of “islands of inversion”, regions of neutron-rich nuclei with conventional magic numbers of neutrons but deformed ground states. On the other hand, new magic numbers were found to develop in nuclei far from stability line, leading to new shell closures. For example, possible new N=32 and N=34 subshell closures were predicted for neutron-rich nuclei around A~50 region. In this talk, I will present the first detailed study of intruder configurations in the ground state of 30Ne via the one-neutron knockout reaction and the first in-beam gamma spectroscopy of 52Ar from the oneproton quasi-free knockout reaction. Both experiments were performed at RIBF at RIKEN using the BigRIPS spectrometer and the DALI2 gamma detector array. The results were discussed in light of shell model and ab-initio calculations and provide direct experimental evidence for the quenching of the N=20 shell gap and the emergence of the new N=34 subshell closure. These new experimental information provides a stringent test for the theory and sheds new light to understand the driving mechanism of shell evolution.