- ed 0018933 againstthe Revalue for Eu)56 and a series of straight lines resulted with slopes ranging from positive to negative values. Pesitive slopes indica- ted a simultaneous enrichment of the cloud particles in europium and the product nuclide, whereas negative slopes showed that as the particles became richer in europium they were more and more depleted in the product nuclide, Products having rare-gas and alkali 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 as Ca, which showed no fractionation with respect to europium, had infinite pesitive slopes, The results. are consistent with the view that these preducts having rare-gas or alkali metal ancestors at the time of condensation will concentrate im the smaller particles which have a larger surface-to-velume ratio, Similar relationships have been found for several high yield air bursts using Ba 140 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-value plots), In this reference system, Agi}, y237, call5, cs!36, Np*??, y?), and sr89 had approximately unit positive slepes while zr??, Cel 44, Pu“? and the of 1.5, age negative slopes er av d ha hs rt ea re ra 33 e was For these shots ther t SAN BREN BE