Experimental study of isospin transport with Ca 40,48 + Ca 40,48 reactions at 35 MeV/nucleon

We investigate the isospin transport with Ca40,48+Ca40,48 reactions at 35 MeV/nucleon, measured with the coupling of the VAMOS high acceptance spectrometer and the INDRA charged particle multidetector. Using the fragment measured with VAMOS and carefully selected light-charged-particles measured in coincidence with INDRA, a reconstruction method is applied to estimate the excited quasiprojectile (QP) on an event-by-event basis. Isospin diffusion is investigated using the isospin transport ratio with the asymmetry δ=(N-Z)/A of the projectile remnant as an isospin-sensitive observable and the total transverse energy of Z≤2 nuclei for experimental centrality sorting. The experimental isospin transport ratios present, for both the reconstructed QP and its remnant, a clear evolution towards isospin equilibration with increasing dissipation of the collision while the full equilibration is not reached. A smoother evolution with less discrepancies between the two mixed systems in the case of the reconstructed QP is also observed. Isospin migration is investigated using the average neutron-to-proton ratio of the light-charged-clusters and the velocity of the QP remnant as a sorting parameter. A systematic neutron-enrichment is observed and interpreted as a consequence of isospin migration, in particular for the symmetric systems which present no isospin gradient between the projectile and the target. We also noticed that the H2 and He4 particles exhibit very close multiplicities independently of the sorting variable for the symmetric systems.