ee 0018933 fusion and with solid particles. The radionuclide atoms present will collide frequently with oxygen atoms or molecules and, since the majority of them are electron donors, metallic oxide molecules will be formed which become thermodynamically stable as the temperature falls. The oxide molecules, or free radionu- clide atoms, also have frequent collisions with the liquid drops of environ- mental material (silica, alumina, iron oxide or calcium oxide) and these collisions may be inelastic since in some cases the incoming molecules will be held by strong attractive forces, The radioactive oxide molecules which condense at the liquid surface will spread into the interior of the drops and become more or less uniformly distributed throughout, Later, after the liquid drops have frozen, the incoming radionuclide molecules may be heldby surface forces, Another way in which the radionuclide molecules may become associated with the environmental material is by participation in the structure of the cluster embryos which are the precursors of the liquid drops (Ref- erences 4 and 6 ), Due to the very low concentrations of the radionuclide oxide molecules, collisions with one another will be relatively infrequent and it appears that the aggregation of enough molecules of this type to form a drop or crystal will be a rare event, if it occurs at all. SAN BRUNO FRE -~spepescssapen