The one-neutron knockout from ${}^{52}\mathrm{Ca}$ in inverse kinematics onto a proton target was performed at $\sim 230\mathrm{MeV}$/nucleon combined with prompt $\gamma$ spectroscopy. Exclusive quasifree scattering cross sections to bound states in ${}^{51}\mathrm{Ca}$ and the momentum distributions corresponding to the removal of $1f_{7/2}$ and $2p_{3/2}$ neutrons were measured. The cross sections, interpreted within the distorted-wave impulse approximation reaction framework, are consistent with a shell closure at the neutron number $N=32$, found as strong as at $N=28$ and $N=34$ in Ca isotopes from the same observables. The analysis of the momentum distributions leads to a difference of the root-mean-square radii of the neutron $1f_{7/2}$ and $2p_{3/2}$ orbitals of 0.61(23) fm, in agreement with the modified-shell-model prediction of 0.7 fm suggesting that the large root-mean-square radius of the $2p_{3/2}$ orbital in neutron-rich Ca isotopes is responsible for the unexpected linear increase of the charge radius with the neutron number.

• Received 9 August 2022
• Revised 24 October 2022
• Accepted 23 November 2022

DOI:https://doi.org/10.1103/PhysRevLett.129.262501

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Published by the American Physical Society