A bubble nucleus to probe the spin-orbit force in extreme conditions
par
Olivier Sorlin(Ganil)
→
Europe/Paris
Salle 101 (LAL)
Salle 101
LAL
Bât.200
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- the r-process) in which the main survivors are
magic nuclei. The SO force has been postulated more than 60 years ago, and
now theoretical descriptions in the framework of relativistic mean field
model exist. However, models differ significantly towards the drip line
for more than 40 years, where SHE may exhibit enhanced stability, and
where the r-process occurs, owing to the fact that this force could never
be tested in such unusual conditions in nuclear densities.
We propose to study for the first time the 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 reaction was used from a 34Si radioactive
beam at the NSCL/MSU (USA) facility to determine its proton (neutron)
density profile, based on the ‘measured' 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 and the bubble nucleus 34Si was determined by using the
neutron adding (d,p) reaction at the GANIL facility in Caen. The protons
were detected in the highly segmented MUST2 detector and the gamma-rays
were detected in coincidence with the EXOGAM segmented Ge array.
Consequences and perspectives related to this study of the SO interaction
will be discussed.