Neutron hole states in 131Sn and spin-orbit splitting in neutron-rich nuclei

R. Orlandi, S.D. Pain, S. Ahn, A. Jungclaus, K.T. Schmitt, D.W. Bardayan, W.N. Catford, R. Chapman, K.A. Chipps, J.A. Cizewski, C.G. Gross, M.E. Howard, K.L. Jones, R.L. Kozub, B. Manning, M. Matos, K. Nishio, P.D. O'Malley, W.A. Peters, S.T. PittmanA. Ratkiewicz, C. Shand, J.F. Smith, M.S. Smith, T. Fukui, J.A. Tostevin, J. Utsuno

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In atomic nuclei, the spin-orbit interaction originates from the coupling of the orbital motion of a nucleon with its intrinsic spin. Recent experimental and theoretical works have suggested a weakening of the spin-orbit interaction in neutron-rich nuclei far from stability. To study this phenomenon, we have investigated the spin-orbit energy splittings of single-hole and single-particle valence neutron orbits of 132Sn. The spectroscopic strength of single-hole states in 131Sn was determined from the measured differential cross sections of the tritons from the neutron-removing 132Sn(d, t)131Sn reaction, which was studied in inverse kinematics at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The spectroscopic factors of the lowest , and states were found to be consistent with their maximal values of , confirming the robust shell closure at 132Sn. We compared the spin-orbit splitting of neutron single-hole states in 131Sn to those of single-particle states in 133Sn determined in a recent measurement of the 132Sn(d, p)133Sn reaction. We found a significant reduction of the energy splitting of the weakly bound 3p orbits compared to the well-bound 2d orbits, and that all the observed energy splittings can be reproduced remarkably well by calculations using a one-body spin-orbit interaction and a Woods–Saxon potential of standard radius and diffuseness. The observed reduction of spin-orbit splitting can be explained by the extended radial wavefunctions of the weakly bound orbits, without invoking a weakening of the spin-orbit strength.
Original languageEnglish
Pages (from-to)615-620
Number of pages6
JournalPhysics Letters B
Early online date7 Aug 2018
Publication statusPublished - 10 Oct 2018


  • Nuclear structure
  • Spin-orbit interaction
  • Transfer reactions
  • Doubly-magic nuclei
  • Shell model


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