Evolution of the Nuclear Spin-Orbit Splitting Explored Via the ^32si(d,p)^33si Reaction Using SOLARIS

The spin-orbit splitting between neutron 1p orbitals at ^33Si has beendeduced using the single-neutron-adding (d,p) reaction in inversekinematics with a beam of ^32Si, a long-lived radioisotope. Reactionproducts were analyzed by the newly implemented SOLARIS spectrometer at thereaccelerated-beam facility at the National Superconducting CyclotronLaboratory. The measurements show reasonable agreement with shell-modelcalculations that incorporate modern cross-shell interactions, but theycontradict the prediction of proton density depletion based on relativisticmean-field theory. The evolution of the neutron 1p-shell orbitals issystematically studied using the present and existing data in the isotonicchains of N=17, 19, and 21. In each case, a smooth decrease in the separationof the 1p_3/2-1p_1/2 orbitals is seen as the respective p-orbitalsapproach zero binding, suggesting that the finite nuclear potential stronglyinfluences the evolution of nuclear structure in this region.