Structure ofN22and theN=14subshell

Abstract

One-neutron knockout data for 18−22 N are analyzed in the eikonal approximation of the Glauber model. The role of the s-d shell and the crossing of the N = 14 neutron subshell are discussed. Of particular interest is the nucleus 22 N, where the knockout data provide a sensitive experimental test for a possible halo structure of its ground state. The observation of a narrow momentum distribution of the 21 N fragments, together with an essential 1s 1/2 contribution needed to describe the observed longitudinal-momentum distribution, allow the firm conclusion that the ground state of 22 N is a well-developed nuclear halo. The results also show that the N = 14 subshell in 22 N is somewhat reduced as compared to that of 23 O.

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

“…Considering an admixture of the 1d 5/2 neutron orbital with the 21 N core in the 3/2 − , 1.16 MeV excited state the data are consistent with a valence neutron probability of 50% -100% in the 2s 1/2 orbital. This agrees within the upper end of the uncertainty band with the momentum distribution measurement [4]. Therefore the evolution of R ex p sheds new light on the halo-like structure in 22 N. The R ex p of 15,18−22 N are consistent with the relativistic mean field (RMF) predictions of Ref.…”

“…The proton radii decrease from 17 N to 21 N with this hint of a minimum reflecting a shell gap at N = 14 in the nitrogen isotopes. The proton radius increases beyond this for 22 N. In a 21 N (core) + n model of 22 N, this shows an enlargement of the core 21 N. The evolution of matter and proton radii reveal thick neutron skins in 18−22 N. One neutron removal reactions show a reduction in the width of the longitudinal momentum distribution (P || ) between 21 N (∆P || =160±32 MeV/c) and 22 N (∆P || = 77±32 MeV/c) that indicates a change of dominating neutron orbitals from l = 2 to l = 0 [4]. The P || for 18,19 N are explained by ∼ 69% probability of the neutron in the l = 2 orbital with the core nucleus in excited states.…”

“…Studies of excited states and momentum distributions have discussed a shell gap at N = 14 between the 1d 5/2 and 2s 1/2 orbitals in oxygen isotopes. However, its reduction for the nitrogen isotopes is signalled and its disappearance due to a level inversion is predicted in the carbon isotopes [4][5][6][7][8][9][10][11][12].…”

Investigation ofN23in a three-body model

“…and their important role in the big bang nucleosysnthesis [11]. For the nitrogen isotopes, many studies have focused on neutronrich isotopes with mass number ranging from A = 17 to A = 22 [12][13][14][15][16][17]. However, 23 N has rarely been investigated since its first production in 1998 [18,19].…”

Ab Initio No Core Shell Model Study of Neutron Rich Nitrogen Isotopes

“…The structure of neutron rich nuclei 19−22 N has been studied by in-beam γ-ray spectroscopy and spectra and other properties are compared with shell model calculations using WBT and WBTM interactions, where N = 14 closed sub shell is discussed [9]. The 22 N has halo structure in its ground state [10,11]. Recently, the point proton radii of neutron rich 17−22 N isotopes have been measured from charge changing cross section in Ref.…”