isodose and isodose rate contour plots will be developed for the two types of explosions, surface-land and surface-water, taking inte account the time of fallout arrivel. Comparisons with other models and with nuclear data will be carried out and the cloud geometry factor exanined. The contricution which these upper yield limit data make to the develorment of scaling relationships can then be fully evaluatec. Improvements of and seneralizations. on the experimental model are exected te accomp ny the foregoing analyses. Use of the method as a tool for forecastinz primary fellout arpears promising and will be exploren, Additional development and evaluation of data on gamma field decay wi11 te carried out. Ideelization of the decay curve from 5 to £00 hr post detonation is expected to produce a simplified appro:dmation suitable for military planning and field use. This approximation may reduce to two straisnt line functions on a logaritumtc plot, one covering the period from 5 to 50 hr, and the other, 50 to 5CU hr. Later decay is assumed to follow the normal fission product function. 763 SPECIFIC CCNCLYSIONS The following conclusions present evaluation of data on primery fallout at CASTLE: (a) Gamma fields fron fallout decayed at rates differing from the t7++2 approximation common to fission weapons. Tne extent of this difference is militarily inportant over certain time periods. (b) Fallout from the surface land detonations was in the forn of irrezular solid particulates. The geometric mean particle diameter decreésed with distance from the shot points; for Shot 1 the peometric mean veried from 112 H at Fikini Atoll to45 p at Utirik Atoll. (c) Of the solid particulates studied, approximately 25 per cent Were inective with their mean particle size smaller than the active. (a) The average density of the solid particles from Shot 1 was 2.36 g/eu cm (e) Little data were obtained on the nature of the fallout from overevater shots. There was some indirect evidence that the fallout 50 nautical miles fron Shot 2 arrived as a fine mist or aerosol. (f) Time and rate of arrival of fallout were documented only within the atolls by Project 2.5a. towever, limited results on more distant isinnIs were obtained for Shot 1. Arrival was characterized by a rapid rise te a peak followed by a decline which, in the measurement of gamma dose-rate, merged imperceptibly with radioactive decay. ‘iaterial first arrived at approximately 1/2 hr after detonation and contimed for 1-1/2 to 2 hr. (g) A contimous 100 hr unshielded exposure after the detonation of a 15-'T device on land will result in a minimum free field total dose of 1% r over an erea as large as 25,000 sq mi. (nh) The development of an experimental model has provided a means of recoistructing fallout patt«rns using limited gamma ficld data end a coiprenensive analysis of the . steorolozical situation as arplici to farticle trajectories. Conclusions as to the usefulness of free-flo-ting buoy stations for 102