Spectroscopy of excited neutron configurations of Ca 54

This is the authors' abstract. We don't add key points for this paper.

Despite its nucleon numbers not coinciding with the traditional nuclear magic numbers, the structure of Ca 54 shows signatures of a doubly closed shell nucleus. This article details the structures of neutron-excited states up to beyond the two-neutron emission threshold populated by the Ca 55 ( p , p n ) reaction at ∼ 200 MeV/nucleon. Level energies and population cross sections were determined through γ -ray spectroscopy and invariant-mass spectroscopy of Ca 54 . Large-scale shell model calculations with protons and neutrons allowed to occupy the s d − p f − s d g orbitals were performed to predict energy levels and spectroscopic factors. Distorted wave impulse approximation calculations provided single-particle knockout cross sections and momentum distributions of the reaction products. The theoretical calculations reproduce the data well. Both theory and experiment are suggestive of a well-preserved shell structure at high excitation energy. Also, inelastic scattering of Ca 54 , carried out within the same experiment, validates previously proposed level schemes.