1.3.6 Overall Approach. It should be emphasized that, at the time this project was conceived, the need for controlled and correlated sets of fallout data for megaton bursts was critical. Be- cause of the lack of experimental criteria, theoretical concepts could be neither proved nor disproved, and progress was blocked by disagreements over fundamental parameters. The distribution of particle sizes and radioactivity within the source cloud, the meteorological factors which determined the behavior of the particles falling through the atmosphere, the relationship of activity to particle size, and the decay and spectral characteristics of the fallout radiations: all were in doubt. Even the physical and chemical nature of the particulate from water-surface bursts was problematical, and all existing model theory was based on land-surface detonations. Corrections necessitated by collection bias and radionuclide fractionation were considered refinements. The objectives stated in Section 1.1 were formulated primarily to provide such sets of data. However, the need to generalize the results so that they could be applied to other combinations of detonation conditions was also recognized, and it was felt that studies relating to basic radiological variables should receive particular emphasis. Only when it becomes possible to solve new situations by inserting the proper values of such detonation parameters as the yield of the device and the composition of environmental materials in generalized mathematical relationships will it become possible to truly predict fallout and combatits effects. 18