Isomeric states in neutron-rich nuclei near N=40

A First Glimpse at the Shell Structure beyond $^{54}$Ca: Spectroscopy of $^{55}$K, $^{55}$Ca, and $^{57}$Ca

“…The two-neutron separation energies extracted from the measured masses [11,12] support the picture of large energy gaps between the neutron 1p 3/2 , 1p 1/2 , and 0f 5/2 orbitals. Recently, the analysis of one-neutron knockout reactions populating states in 53 Ca further supported the magicity of 54 Ca [13]. In particular, the shell model picture describing the ground state of 54 Ca with fully occupied neutron 1p 1/2 and 1p 3/2 orbitals and an empty 0f 5/2 orbital was corroborated by these findings.…”

“…In contrast to 55 Ca, the excited state observed in 57 Ca is populated in the proton removal reaction from its isotone 58 Sc. The latter nucleus has been discussed as a member of the island of inversion centered around 64 Cr and shell model calculations with the LNPS effective interaction [17] show that the wave functions of low-lying states contain significant contributions from particle-hole configurations [53]. The quasi-free (p, 2p) reaction on such a system is likely to leave the neutron configuration untouched and, therefore, will populate states with neutron particlehole excitations.…”

“…Since the ground state spin and parity of 58 Sc are not known and this nucleus furthermore has at least one longlived isomeric state [53], meaningful spectroscopic factors cannot be extracted from the experimental cross section. The LSSM and VS-IMSRG calculations are able to predict spectroscopic factors.…”