Argonne National Laboratory

Effect of weak binding on the apparent spin-orbit splitting in nuclei

By Vic ComelloNovember 30, 2017

Scientific achievement

This work shows that the decrease in the spin-orbit splitting between the neutron p-states outside the N = 20 closed neutron shell in 41Ca, 39Ar, 37S, and 35Si is a result of the change in the binding energy of the spin-orbit partners with respect to the neutron threshold.

Significance and impact

Researchers have calculated that effects on the energies of excitation in nuclei can depend on how tightly the last neutron or proton is bound. The present collaboration showed that a geometric effect that causes the separation between two excitations to change can explain experimentally observed effects with no need to assume exotic “bubble” influences.

Research details

  • Researchers described the changes observed experimentally for 1p3/2 and 1p1/2 states from Ca to Si in terms of the proximity of the 1p1/2 orbital to the neutron threshold.
  • To explore such effects, researchers carried out calculations with a Woods-Saxon potential using the code of Volya [1] and several established parameter sets characterizing the neutron-nucleus potential.

Work performed at 1Argonne National Laboratory and 2Lawrence Berkeley National Laboratory by B.P. Kay1, C.R. Hoffman1, and A.O. Macchiavelli2, Phys. Rev. Lett., 119, 182502 (2017) DOI:
This research was funded by the U.S. Department of Energy’s Office of Nuclear Physics.


[1] A. Volya,

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