Shell Migration at N = 32, 34 around Ca Region

Abstract

The neutron numbers N = 32 and 34 are new magic numbers suggested in neutron-rich $pf$-shell nuclei. In this article, we discuss the experimental observables and state-of-the-art theoretical calculations that characterize and explain the shell evolution leading to new magic numbers. Particular focus shall be afforded to the experimental progress of the shell migration study at and beyond N = 32, 34 in Ar, K, Ca, and Sc isotopes at the RIBF using direct reactions with liquid hydrogen targets over the past ten years. The results prove the double magicity of \ts{52,54}Ca, and support the persistence of the N = 34 subshell closure below Z = 20 with a sharp weakening beyond Z = 20. Future measurements of intruder bands of N = 32, 34 nuclei and shell evolution towards N = 40 are discussed within the context of an upgraded RIBF facility and the development of novel detection systems.