Abstract
Background
The recent discovery and spectroscopic measurements of 27O and 28O suggests the disappearance of the N = 20 shell structure in these neutron-rich oxygen isotopes.
Purpose
We measured one- and two-proton removal cross sections from 27F and 29Ne, respectively, extracting spectroscopic factors and comparing them to shell model overlap functions coupled with eikonal reaction model calculations.
Method
The invariant mass technique was used to reconstruct the two-body (24O + n) and three-body (24O + 2n) decay energies from knockout reactions of 27F (106.2 MeV/u) and 29Ne (112.8 MeV/u) beams impinging on a 9Be target.
Results
The one-proton removal from 27F strongly populated the ground state of 26O and the extracted cross section of 3.4+0.3−1.5 mb agrees with eikonal model calculations that are normalized by the shell model spectroscopic factors and account for the systematic reduction factor observed for single nucleon removal reactions within the models used. For the two-proton removal reaction from 29 Ne an upper limit of 0.08 mb was extracted for populating states in 27O decaying though the ground state of 26O.
Conclusions
The measured upper limit for the population of the ground state of 26O in the two-proton removal reaction from 29Ne indicates a significant difference in the underlying nuclear structure of 27F and 29Ne.