Abstract
The evolution of the traditional nuclear magic numbers away from the valley of stability is an active field of research. Experimental efforts focus on providing key spectroscopic information that will shed light into the structure of exotic nuclei and understanding the driving mechanism behind the shell evolution. In this work, we investigate the Z=6 spin-orbit shell gap towards the neutron dripline. To do so, we employed NA(p,2p)CA−1 quasi-free scattering reactions to measure the proton component of the 21+ state of 16,18,20C. The experimental findings support the notion of a moderate reduction of the proton 1p1/2−1p3/2 spin-orbit splitting, at variance to recent claims for a prevalent Z=6 magic number towards the neutron dripline.
Highlights
The emergence of nuclear magic numbers within a shell-model description of atomic nuclei has been the paradigm of our understanding of nuclear structure
Residual interaction, the magic numbers that emerge near the stability line are not necessarily the same for exotic nuclei, which have large neutron-proton asymmetry, see e.g. Ref. [4] and references therein
Following on from Refs. [5,7,8], we report in this Letter the results of an experiment designed to study the proton component of the 2+1 state in 16,18,20C using Quasi-Free Scattering (QFS) (p,2p) reactions on 17,19,21N
Summary
In our earlier work [5] we have attributed the observed increase in the B(E2; 2+1 → 0+1 ) values from 16C to 20C, as a manifestation of increased in-shell proton excitations (p11/2 p−3/12), due to a weakening of the 1p1/2 − 1p3/2 spin-orbit splitting at Z = 6 towards the dripline. It is worth pointing out a similar effect has been discussed in Ref.
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