0018933 media. Determination of the soluble fraction is therefore an important problem and solubility studies have been reported on fallout from several of the shots at Operations CASTLE and REDWING. For CASTLEfallout, it was found that the seluble fraction was strongly dependent on the detonation environment, being around 0.05 for land shots and 0. 58-0. 73 for shots fired from a barge (Reference 15}, The solubility in seawater of the fallout from the reef shot Tewa, Operation REDWING, was investigated in two ways: by leaching of particles placed on top of a glass wool column and by centrifuging a suspension of the fallout material (Reference 13). The soluble fractions found by these two methods were 0.08 and 0.18, respectively, | An ultrafiltration method was used for determining the solubility of fallout from the land shot, Zuni, About 25% of the total gamma activity and Np??? were soluble in seawater and 5% of the total gamma activity was soluble in rainwater. 1.2.2 Cloud Development. During the later stages of existence of the fireball, it is transformed into a vortex ring whose rotational velocity persists up to the maximum cloud altitude, at least for the larger shots, The vortex contains the fission products, emvironmental material and bomb components which were present in the fireball and is the site where the radioactive fallout particles are generated, The cloud continues to rise until its buoyancy is reduced to zero by adiabatic expansion, entrainment 19 SAN BRUNO FRE 14