CHAPTER 7 SUMMARY Prediction of the downwind area of primary fall-out with a high degree of confidence early enough to establish a selective station array to cover the area cannot be satisfactorily ac- complished. The limited climatological data available for the Marshall Islands indicate the most probable direction of the winds aloft during the fall and winter months to be from the east for heights of approximately 20,000 ft and from the west for heights between 20,000 and 100,000 ft. However, the wind profile at shot time indicated that the primary fall-out following Mike shot was deposited to the northwest of Eniwetok Atoll. It is noteworthy that during the two weeks prior to shot time, the daily variation in the wind profile was of such magnitude that a 24-hr forecast of the fall-out area would have been in error in the majority of cases. However, if the winds aloft are known at the time of detonation, it is possible to predict quite accurately the distribution of ground contamination resulting from radioactive fall-out. Observation of the documentary photography taken of Mike shot, Operation Ivy, indicated no evidence of a base surge following the detonation. Although the major portion of this film did not record surface phenomena, those portions documenting the surface of the lagoon after the event do not show a base surge. The fall-out particulate, being primarily compounds of calcium, was peculiar to a coral atoll, The main contribution to the radiation field was the fission product mixture trapped within these particulates. The particle density was between | and 3 g/cu cm in the majority of cases and similar to that of many soils. Although there was not a great quantity of fall-out at any location, the individual particles were very active, some reading as high as 300 mr hr of beta-gamma radiation 48 hr after shot time. The activity was easily leached from the particulate by the action of rain water. The particle reaction with the sulfate ions in sea water caused them to become hollow and to adhere to any surface they touched, This behavioris probably the most significant observation of the effect of the environmenton the particles. 7.1 CONCLUSIONS In summarizing the work done on this project, it is convenient to state the conclusions as they specifically apply to either the primary or secondaryfall-out. 7.1.1 Primary Fall-out The gamma-radiation field at the cessation of the primary fall-out varied from about 800 r/hr at 2 hr and 3 miles distance to 0 r/hr at a cross-wind distance of approximately 15 miles. There was no residual radiation field over the open water of the lagoon. Evidently the radioactive particulate immediately settled to the bottom. The gamma decaycurve for the radioactive fall-out has a slope of approximately -1.2. 54 eee