DNA 1240H-2 each disc for each particle-size class until the diec hite the ground. The effect of this process is to determine the distribution of fallout by tracking 8 maximm of 9000 different discs (depending on yield), each representing a given particle-size range originating at a given altitude in the cloud. The fraction of activity associated with each particlesize clase must also be known, to permit deposit dose-rate estimates. Dose-rate and dose values calculated from this model are in agreement with measurements made following the surface and underground shots of Operation Jangle. Use of the D-Model to predict reasonably accurate fallout contours for water-surface bursts will be possible only with several fundamental changes of parameters used in the computer program. Weapons-test data rates are different from those of earth particles. It follows, there- have indicated that slurry-type fallout droplets from water-surface bursts differ from land-surface-burst fallout particles in size range, composition, density, and mass-activity relationships. In addition, the time-history of the formation of slurry droplets and their falling fore, that fallout patterns for water-surface bursts would differ from those for land-surface bursts. Furthermore, it must be understood that there is no such thing as a dose-rate contour at sea because fallout mixes fairly rapidly with the water, although on a large ship located at a fixed point, deposit dose could build up as on a land target. Work is in progress at NRDL to determine the required changes in parameter values that would permit application of the D-Model to water-surface- burst fallout prediction. When the appropriate program changes are effected, the output of the D-Model will indicate deposit that would take piace on @ large, flat, unwashed surface, and must be interpreted, together with ship size and countermeasure system, to provide dose or dose rate information. Predictions that are given in Ref. & for deposit dose from a water-surface shot have been based on a compromise of predictions of effects of a land-surface shot as given in Refs. 2 and 69, and as com- puted from the lami-surface D-Model. 67 It has been impossible to determine the degree of accuracy of the predictions of Ref. &, since no water-surface shot of this type has been fired. It was assumed that the base surge is a minor mechanism of transport of radioactivity, that fallout from the cloud is the main source of deposited activity, and that the cloud dimensions are comparable to or exceed those of the base surge. It was further assumed that the deposited activity builds up in @ linear manner with time during the period of deposition. The times of initial arrival and final arrival of activity were estimated on the pasis of fallout from the cloud as determined by the falling rates of icles and by the assumed prevailing winds. Then the deposit dose, » accumilated at a point during the time interval from ty, time of jnitial arrival of activity, to any time after burst, t, may be expressed y: t De dat & BEST AVAILABLE COPY 17-78 (17-24)