 Here, formula_16 expresses the rate of incoming matter and formula_11 is the probability that a nucleus of critical size (at the maximum of the energy barrier) will continue to grow and not dissolve.The Zeldovich factor is derived by assuming that the nuclei near the top of the barrier are effectively diffusing along the radial axis.By statistical fluctuations, a nucleus at the top of the barrier can grow diffusively into a larger nucleus that will grow into a new phase, or it can lose molecules and shrink back to nothing.