  Using transport theory to model central Au + Au collisions in the energy
region of 20 - 110 MeV/u, at impact parameters b <= 5 fm, we predict a
measurable impact of spinoidal instability as the collective expansion sets in
with energy. Two transport models are employed, the pBUU model, solving a
Boltzmann-Uehling-Uhlenbeck equation, and the Brownian Motion (BM) model,
solving a set of Langevin equations to describe the motion of individual
nucleons in a noisy nuclear medium. We find without ambiguity, for the first
time, that a combination of delayed equilibration, onset of collective
expansion and the spinodal instability produces a pair of transient ring
structures, made of the projectile and target remnants, with spectator nucleons
predicted to end in the entities reminiscent of stones in jewelry, on the
rings. The ring structures, calculated in the configuration space and mapped
onto the velocity space, could be detected in experimental collective flow
data.
