Reduction of the Spin-Orbit Splittings at the N=28 Shell Closure

L. Gaudefroy (1, 2) , O. Sorlin (1, 2) , D. Beaumel (1) , Y. Blumenfeld (1) , Z. Dombrádi , S. Fortier (1) , S. Franchoo (1) , M. Gélin (2) , J. Gibelin (1) , S. Grévy (2) , F. Hammache (1) , F. Ibrahim (1) , K. W. Kemper , K.-L. Kratz , S. M. Lukyanov , C. Monrozeau (1) , L. Nalpas (3) , F. Nowacki (4) , A. N. Ostrowski , T. Otsuka , Yu.-E. Penionzhkevich , J. Piekarewicz , E.C. Pollacco (3) , P. Roussel-Chomaz (2) , E. Rich (1) , J. A. Scarpaci (1) , M.G. Saint-Laurent (2) , D. Sohler , M. Stanoiu , T. Suzuki , E. Tryggestad (1) , D. Verney (1)

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

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.

Mots clés: 2H-induced transfer reactions; Nuclear spectroscopic factors; Nuclear single-particle levels and strength functions; Properties of nuclei with 39 <= A <= 58

Domaines: Physique Nucléaire Expérimentale [nucl-ex]

L. Gaudefroy, O. Sorlin, D. Beaumel, Y. Blumenfeld, Z. Dombrádi, et al.. Reduction of the Spin-Orbit Splittings at the N=28 Shell Closure. Physical Review Letters, 2006, 97, pp.092501. ⟨10.1103/PhysRevLett.97.092501⟩. ⟨in2p3-00090839⟩