Eur. Phys. J. A (2012) 48: 191
https://doi.org/10.1140/epja/i2012-12191-5

Regular Article - Experimental Physics

One-neutron knockout from ^51–55 Sc

¹ Physik Department E12, Technische Universität München, 85748, Garching, Germany
² TRIUMF, 4004 Wesbrook Mall, V6T 2A3, Vancouver, Canada
³ Department of Physics & Astronomy, University of British Columbia, V6T 1Z1, Vancouver, Canada
⁴ Institut für Kernphysik, Technische Universität Darmstadt, 64289, Darmstadt, Germany
⁵ Departamento de Física de Partículas, Universidade de Santiago de Compostela, 15782, Santiago de Compostela, Spain
⁶ GSI Helmholtzzentrum für Schwerionenforschung, 64291, Darmstadt, Germany
⁷ Instituto de Estructura de la Materia, CSIC, 28006, Madrid, Spain
⁸ SAFE/OCL, University of Oslo, N-0316, Oslo, Norway
⁹ CEA, DSM/IRFU/SPhN, F-91191, Gif-sur-Yvette, France
¹⁰ University of Vigo, Vigo, E-36310, Spain
¹¹ NSCL, Michigan State University, 48824, East Lansing, Michigan, USA
¹² Experimentell Fysik, Chalmers Tekniska Högskola och Göteborgs Universitet, 412 96, Göteborg, Sweden
¹³ Saint Mary’s University, 923 Robie St., B3H 3C3, Halifax, Canada
¹⁴ Johannes Gutenberg Universität, 55099, Mainz, Germany
¹⁵ Paul Scherrer Institut, 5232, Villigen, Switzerland
¹⁶ Institut Pluridisciplinaire Hubert Curien, IN2P3-CNRS/Université Louis Pasteur, F-67037, Strasbourg Cedex 2, France
¹⁷ Nuclear Physics Division, Bhabha Atomic Research Centre, 400 085, Mumbai, India
¹⁸ Faculty of Mathematics and Physics, Comenius University, 84215, Bratislava, Slovakia
¹⁹ Department of Physics, University of Tokyo, Hongo, Bunkyo-ku, 113-0033, Tokyo, Japan
²⁰ Department of Physics, Faculty of Engineering and Physical Sciences, University of Surrey, Surrey GU2 7XH, Guildford, UK
²¹ Garsington, OX44, Oxfordshire, UK

Received: 9 October 2012
Revised: 5 November 2012
Accepted: 1 December 2012
Published online: 20 December 2012

Abstract

Results are presented from a one-neutron knockout experiment at relativistic energies of 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 , , (L = 1 and , (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 to the 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 obtained by evolving a chiral N3LO nucleon-nucleon potential.