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Physical Review Letters 97 (2006) 092501
Reduction of the Spin-Orbit Splittings at the N=28 Shell Closure
L. Gaudefroy1, 2, O. Sorlin1, 2, D. Beaumel1, Y. Blumenfeld1, Z. Dombrádi, S. Fortier1, S. Franchoo1, M. Gélin2, J. Gibelin1, S. Grévy2, F. Hammache1, F. Ibrahim1, K. W. Kemper, K.-L. Kratz, S. M. Lukyanov, C. Monrozeau1, L. Nalpas3, F. Nowacki4, A. N. Ostrowski, T. Otsuka, Yu.-E. Penionzhkevich, J. Piekarewicz, E.C. Pollacco3, P. Roussel-Chomaz2, E. Rich1, J. A. Scarpaci1, M.G. Saint-Laurent2, D. Sohler, M. Stanoiu, T. Suzuki, E. Tryggestad1, D. Verney1
SPIRAL Collaboration(s)

The N=28 shell closure has been investigated via the 46Ar(d,p)47Ar transfer reaction in inverse kinematics. Energies and spectroscopic factors of the neutron p3/2, p1/2, and f5/2 states in 47Ar were determined and compared to those of the 49Ca isotone. We deduced a reduction of the N=28 gap by 330(90) keV and spin-orbit weakenings of ~=10(2) and 45(10)% for the f and p states, respectively. Such large variations for the f and p spin-orbit splittings could be accounted for by the proton-neutron tensor force and by the density dependence of the spin-orbit interaction, respectively. This contrasts with the picture of the spin-orbit interaction as a surface term only.
1 :  IPNO - Institut de Physique Nucléaire d'Orsay
2 :  GANIL - Grand Accélérateur National d'Ions Lourds
3 :  DAPNIA - Département d'Astrophysique, de physique des Particules, de physique Nucléaire et de l'Instrumentation Associée
4 :  DRS-IPHC - Département Recherches Subatomiques
Physique/Physique Nucléaire Expérimentale
2H-induced transfer reactions – Nuclear spectroscopic factors – Nuclear single-particle levels and strength functions – Properties of nuclei with 39 <= A <= 58