Bastin, B, Grevy, S, Sohler, D, Sorlin, O, Dombradi, Z, Achouri, N L, Angelique, J C, Azaiez, F, Baiborodin, D, Borcea, R et al, Bourgeois, C, Buta, A, Burger, A, Chapman, R, Dalouzy, J C, Dlouhy, Z, Drouard, A, Elekes, Z, Franchoo, S, Iacob, S, Laurent, B, Lazar, M, Liang, X, Lienard, E, Mrazek, J, Nalpas, L, Negoita, F, Orr, N A, Penionzhkevich, Y, Podolyak, Z, Pougheon, F, Roussel-Chomaz, P, Saint-Laurent, M G, Staniou, M, Stefan, I, Nowacki, F and Poves, A (2007) Collapse of the N=28 Shell Closure in Si-42 Physical Review Letters, 99 (2).
The energies of the excited states in very neutron-rich Si-42 and P-41,P-43 have been measured using in-beam gamma-ray spectroscopy from the fragmentation of secondary beams of S-42,S-44 at 39A MeV. The low 2(+) energy of Si-42, 770(19) keV, together with the level schemes of P-41,P-43, provides evidence for the disappearance of the Z=14 and N=28 spherical shell closures, which is ascribed mainly to the action of proton-neutron tensor forces. New shell model calculations indicate that Si-42 is best described as a well-deformed oblate rotor.
Published in <i>Physical Review Letters,</i> Vol. 99, Iss. 2. Copyright 2007 American Physical Society. Click <a href=http://prl.aps.org/>here</a> to access the journal's website.