DREB Conference 2024

Neutron-rich calcium isotopes show interesting features exhibiting non-canonical neutron shell closures at N=32 and N=34, while their charge radii [1] show a sharp increase after N=28 which is not reproduced by microscopic theories. Matter radii [2] from interaction cross-section measurements indicate that the increase in size of neutron-rich calcium isotopes is mainly due to neutrons and that a core swelling mechanism is at play [3].
Recently, the proton-induced neutron knockout reaction on ${}^{52}$Ca proved to be able to quantify the size of the p${}_{3/2}$ and f${}_{7/2}$ neutron single-particle orbital using the analysis of the momentum distributions [4]. The result revealed a large p${}_{3/2}$ neutron orbital, 0.61 fm larger compared to the f${}_{7/2}$ neutron single-particle orbital, which may explain [5] the large charge radius values obtained for the neutron-rich calcium isotopes [1].
This analysis was extended to ${}^{53}$Ca and ${}^{54}$Ca for the neutron orbitals, giving consistent results with the first findings, as well as for ${}^{52}$Ca, ${}^{54}$Ca, and ${}^{55}$Sc for the proton single-particle orbitals. The latest results will be shown in this presentation.
The nucleon knockout direct reaction proves to be a valuable tool, sensitive to the size of the single-particle orbitals - a quantity that has not been deeply explored so far for exotic beams.

References:
[1] R. F. Garcia Ruiz et al., Nature Physics 12, 594–598 (2016).
[2] M. Tanaka et al., Phys. Rev. Lett. 124, 102501 (2020).
[3] W. Horiuchi and T. Inakura Phys. Rev. C 101, 061301(R) (2020).
[4] M. Enciu et al., Phys. Rev. Lett. 129, 262501 (2022).
[5] J. Bonnard, S. M. Lenzi, and A. P. Zuker, Phys. Rev. Lett. 116, 212501 (2016).