Droplet formation in expanding nuclear matter: a system-size dependent   study
  Cluster production is investigated in central collisions of Ca+Ca, Ni+Ni, 96Zr+96Zr, 96Ru+96Ru, Xe+CsI and Au+Au reactions at 0.4A GeV incident energy. We find that the multiplicity of clusters with charge Z > 2 grows quadratically with the system's total charge and is associated with a mid-rapidity source with increasing transverse velocity fluctuations. 
FOPI Collaboration: W. Reisdorf, et al