  In a Relativistic Diffusion Model (RDM), the evolution of net-proton rapidity
spectra with sqrt(s_NN) in heavy systems is proposed as an indicator for local
equilibration and longitudinal expansion. The broad midrapidity valley recently
discovered at RHIC in central Au + Au collisions at sqrt(s_NN)= 200 GeV
suggests rapid local equilibration which is most likely due to deconfinement,
and fast longitudinal expansion. Rapidity spectra of produced charged hadrons
in d + Au and Au + Au systems at RHIC energies and their centrality dependence
are well described in a three-sources RDM. In central collisions, about 19 % of
the produced particles are in the equilibrated midrapidity region for d + Au.
