Speaker
Description
In nuclei far from stability, close to the neutron dripline, shell evolution is known to give rise to intricate nuclear structure, new magic numbers and halo nuclei. The formation of a new sub-shell closure at N = 32 in the neutron-rich pf-shell nuclei was reported based on a series of observations relying on E(2+) systematics, transition probability and mass measurements. Charge radii measurements show a linear increase after N = 28 in the Calcium-chain region [1,2], which were interpreted to challenge the magic character of N = 32. Recent theoretical calculations [3] suggest that halo-like p$_{3/2}$ and p$_{1/2}$ neutron orbitals, with the size $\sim$0.7fm larger than f$_{7/2}$ in this neutron-rich region, could explain the observed behavior in the charge radii measurements.
I will present in this talk one neutron-knockout reaction measurements performed on $^{52}$Ca in inverse kinematics at $\sim$260 MeV/u beam energy on a 151-mm-long liquid hydrogen target at the RIBF facility. A systematic comparison of neutron-removal cross-sections from orbitals below and above shell closure, between $^{52}$Ca and the well-established doubly-magic Ca-isotopes, $^{48}$Ca and $^{54}$Ca, corroborate the magicity of N = 32. In addition, the extracted rms of the p$_{3/2}$ and f$_{7/2}$ single-particle orbitals from the measured momentum distributions in $^{52}$Ca(p,pn) reaction is in line with the theoretical calculations and supports the halo nature of the p$_{3/2}$ neutron orbital.
To summarize, our results provide direct evidence for the N = 32 subshell closure and are in agreement with a 'huge' p$_{3/2}$ neutron orbital and the increased charge radius of $^{52}$Ca.
[1] Koszorús, Á., Yang, X.F., Jiang, W.G. et al. Charge radii of exotic potassium isotopes challenge nuclear theory and the magic character of N=32. Nat. Phys. 17, 439–443 (2021)
[2] Garcia Ruiz, R., Bissell, M., Blaum, K. et al. Unexpectedly large charge radii of neutron-rich calcium isotopes. Nature Phys 12, 594–598 (2016)
[3] J. Bonnard, S.M. Lenzi, and A.P. Zuker. Neutron Skins and Halo Orbits in the sd and pf Shells. Phys. Rev. Lett. 116, 212501 (2016)
| Topic | Experiment |
|---|
