0018933 . against the R-value for Eul56 and a series of straight lines resulted with slopes ranging from positive to negative values. Positive slopes indica- ted 2 simultaneous enrichment of the cloud pzrticles in europium and the product nuclide, whereas negative slopes showed that 2s the particles became richer in europium they were more and more depleted in the product nuclide, Products having rare-gas and alkzli metal precursors had the steepest negative slopes while U, Np and Pb had small negative slopes, The more refractory oxide elements Nd, Be, Zr and Nb had positive slopes and those elements such 2s Cz, which showed no fractionation with respect to eurcpium, had infinite positive slopes, The results are conzistent with the view that those products having rare-gzs or alkali | meti? ancestors at the time of condensation will concentrate iz the smaller particles which have a larger surface-tc-vclume ratio. Similar relationships have been found for several high yield air bursts using Ba! 40 as the secondary reference nuclide and Mo 99 as the primary reference nuclide (the primary reference nuclide is the substance used as reference in calculating the R-values; the secondary reference nuclide is the substance used as abscissa in the R-valve plots). In this reference system, Ag!!l, ue37, calls, csi36 Np2?7, y?!}, and sr®°9 had zpproximately unit positive slopes while zr? cel 44, Pat? end the rare earths had average negative slopes of 1,5, For these shots there was