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Description
The spin orbit(SO) force plays a crucial role in nuclear structure to create most of the shell gaps and magic nuclei. It is essential as well to account for a possible island of stability in the superheavy nuclei (SHE) as well as to model explosive stellar nucleosynthesis (such as the rapid neutron capture process) in which the main survivor nuclei are magic nuclei. The SO force has been postulated more than 60 yearsago, and now theoretical descriptions in the framework of relativist mean field model exist. However, models differ significantly towards the drip line where SHE or r process nuclei should exist, owing to the fact this force could never be tested in such unusual or exotic conditions.
We propose to study these unknown components (density and isospin dependence) of the SO force by using the doubly-magic bubble nucleus 34Si, in which a central proton density depletion is present. The one proton (neutron) knockout reactions were used from a 34Si radioactive beam at the NSCL/MSU facility to determine its proton (neutron) density profile, based on the ‘ easured' occupancies of the proton (neutron) orbits. The 33Al (33Si) residues were identified by the S800 spectrometer in coincidence with their gamma-rays detected in the Gretina array. In a second experiment the change of the neutron SO between a normal nucleus 36S or 40Ca and the bubble nucleus 34Si was determined by using the neutron adding (d,p) reaction at GANIL. The protons were detected in the highly segmented MUST2 detector and the gamma-rays were detected in coincidence with the EXOGAM array. Conclusions about the understanding of the SO interaction and future perspectives related to this study will be given at the end.