One-neutron knockout from 51-55Sc

The European Physical Journal A

48
191
(2012)
S. Schwertel, P. Maierbeck, R. Krücken, R. Gernhäuser, T. Kröll, H. Alvarez-Pol, F. Aksouh, T. Aumann, K. Behr, E.A. Benjamim, J. Benlliure, V. Bildstein, M. Böhmer, K. Boretzky, M.J.G. Borge, A. Brünle, A. Bürger, M. Caamaño, E. Casarejos, A. Chatillon, L.V. Chulkov, D. Cortina-Gil, J. Enders, K. Eppinger, T. Faestermann, J. Friese, L. Fabbietti, M. Gascón, H. Geissel, J. Gerl, M. Gorska, P.G. Hansen, B. Jonson, R. Kanungo, O. Kiselev, I. Kojouharov, A. Klimkiewicz, T. Kurtukian, N. Kurz, K. Larsson, T. Le Bleis, K. Mahata, L. Maier, T. Nilsson, C. Nociforo, G. Nyman, C. Pascual-Izarra, A. Perea, D. Perez, A. Prochazka, C. Rodriguez-Tajes, D. Rossi, H. Schaffner, G. Schrieder, H. Simon, B. Sitar, M. Stanoiu, K. Sümmerer, O. Tengblad, H. Weick, S. Winkler, B. A. Brown, T. Otsuka, J. A. Tostevin, W.D.M. Rae

Results are presented from a one-neutron knockout experiment at relativistic energies of 
≈
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 
𝜈
𝑝
1
/
2
 , 
𝜈
𝑝
3
/
2
 , (L = 1 and 
𝜈
𝑓
7
/
2
 , 
𝜈
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 
𝜈
𝑓
7
/
2
 to the 
𝜈
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
𝑙
𝑜
𝑤
𝑘
 obtained by evolving a chiral N3LO nucleon-nucleon potential.

DOI
10.1140/epja/i2012-12191-5
Published on
nwarr