, 48:191
Date: 20 Dec 2012

One-neutron knockout from 51–55 Sc

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Results are presented from a one-neutron knockout experiment at relativistic energies of \( \approx 420 A\) MeV on 51-55Sc using the GSI Fragment Separator as a two-stage magnetic spectrometer and the MINIBALL array for gamma-ray detection. Inclusive longitudinal momentum distributions and cross-sections were measured enabling the determination of the contributions corresponding to knockout from the \( \nu p_{1/2}\) , \( \nu p_{3/2}\) , (L = 1 and \( \nu f_{7/2}\) , \( \nu f_{5/2}\) (L = 3 neutron orbitals. The observed L = 1 and L = 3 contributions are compared with theoretical cross-sections using eikonal knockout theory and spectroscopic factors from shell model calculations using the GXPF1A interaction. The measured inclusive knockout cross-sections generally follow the trends expected theoretically and given by the spectroscopic strength predicted from the shell model calculations. However, the deduced L = 1 cross-sections are generally 30-40% higher while the L = 3 contributions are about a factor of two smaller than predicted. This points to a promotion of neutrons from the \( \nu f_{7/2}\) to the \( \nu p_{3/2}\) orbital indicating a weakening of the N = 28 shell gap in these nuclei. While this is not predicted for the phenomenological GXPF1A interaction such a weakening is predicted by recent calculations using realistic low-momentum interactions \( V_{low k}\) obtained by evolving a chiral N3LO nucleon-nucleon potential.

Communicated by J. Äystö