  Two exponents, $\delta$, for size distribution of $n$-atom clusters,
$Y(n)\sim n^{-\delta}$, have been found in Au clusters sputtered from embedded
Au nanoparticles under swift heavy ion irradiation. For small clusters, below
12.5 nm in size, $\delta$ has been found to be 3/2, which can be rationalized
as occurring from a steady state aggregation process with size independent
aggregation. For larger clusters, a $\delta$ value of 7/2 is suggested, which
might come from a dynamical transition to another steady state where
aggregation and evaporation rates are size dependent. In the present case, the
observed decay exponents do not support any possibility of a thermodynamic
liquid-gas type phase transition taking place, resulting in cluster formation.
