The 1p single-particle energies in neutron-rich nuclei around N∼ 20 suggest a smooth decrease in the separation of the 1p3/2-1p1/2 spin-orbit splittings as they approach zero binding. The behavior is well described by the orbits approaching the zero-binding threshold in a finite mean-field potential but is at odds with the well-accepted scaling of measured spin-orbit splittings across the chart of nuclides for well-bound states. We present the contrast between experimental data, the mean-field description, and the trends established by Mairle [Phys. Lett. B 304, 39 (1993)] for both well-bound and weakly-bound systems across the nuclear chart. The main focus is on low-ℓ neutron spin-orbit partners. This week's ISS experiment is intertwined with this story.
