Neutron skin and signature of the N = 14 shell gap found from measured proton radii of 17−22N

Measurement of proton-distribution radii of neutron-rich nitrogen isotopes

“…For stable isotopes (e.g. 10 B, 12−14 C, 14 N), the obtained proton-distribution radii are in good agreement with the electron-scattering data [7,9,10]. The extracted point-proton-distribution radii (R p ) from σ CC are shown in Fig.…”

“…of 22 N is different from that of the 21 N core which leads to the c.m. motion and hence it smears the core density, resulting in a larger core size [7]. Similar phenomenon has been observed in the two neutron halo 11 Li [12] and 6 He [13] isotopes.…”

“…1, the relativistic mean field (RMF) predictions [11] are shown which are consistent with the experimental data. Ab initio, in-medium similarity re-normalization group, calculations with a stateof-the-art chiral nucleon-nucleon and three-nucleon interaction reproduce well the data towards the neutron dripline isotopes rather than the whole isotopic trend of the radii [7].…”

“…The matter-distribution radii can be obtained from the measured interaction cross sections [14] using the finiterange Glauber model framework. Together with the information on the matter-distribution and proton-distribution radii, thick neutron skins for 19−21 N, have been found, while for 22 N a neutron halo-like structure develops [7].…”

“…For nitrogen isotopes, the proton-neutron tensor interaction is attractive for p(1p 1/2 )-n(1d 5/2 ) orbitals, thereby reducing the gap between proton 1p 1/2 and 1p 3/2 orbitals when more neutrons are added to the 1d 5/2 orbital, resulting in a small point proton radius in 21 N. This attractive interaction also lowers the neutron 1d 5/2 orbital leading to the N = 14 shell gap [7] in neutron-rich nitrogen isotopes.…”