For a single plate the separation factor 5 depends only on the dimension-less time τ =Dt/Z2and the difference between the diffusion coefficients ΔD.The output for a certainScan be increased linearly with the plate thickness while simultaneously the diffusion time increases with the square of the plate thickness. For a cascade of 2 plates of equal thickness, the time scale for equalSis expanded by a factor 4 against the single plate. Simultaneously the output is increased by a factor 4β, where β is the efficiency coefficient for the transfer between the 2 plates.