Carlos Tun Locetion i hE Dae Cte DD Th F . 273 3--/4F#o- A— Polscr_(96¢ |GOS ee 410592 CASTIE LOCAL FALL-OUT FORECASTING 1. The method of calculating local fall-out, as described here, is the hasty outgrowth of a more complex method that had been unexpectedly successful in accounting for the BRAVO fall-out pattern in the Alingnac-Rongelap~Rongerik area. As the time of the last shot (on Eniwetok Atoll) approached, the problem of forecasting local fall-out became more acute. Since the method att enpted to take account of the initial size and shape of the cloud, it seemed that it should be suitable for local forecasting. With the aid of Dr. Gaslen Felt, the method was simplified to the extent that an atoll pattern could be” estimated within about an hour, the simplified method was tested against the Bikini patterns produced by ROMEO, UNION and YANKEE and found satisfactory,” and the method was used in forecasting for NECTAR. 2. The following description covers the simplified method only. The mre complex method warrants further study which will be reported elsewhere, 3. Assumptions: (a) The initial cloud (after rise 4s practically completed) is divided into horizontal slices, each of 10,000 ft depth, with centers at 10,000, 20,000, = = = = 70,000 ft altitude, with the central concentration (radioactivity per unit volume) independent of eltitude, (b) In each layer all of the activity lies in a horizontal plane thru the center. (c) In each layer, the concertration falls off laterally according to the law of normal distribution of errors c (r) =Coe =, &o where Co is the initial central concentration, r is distance from center, and COPIED/DOE % LAN! RO” 5 | BEST COPYAVAILABLE ~/