which are the residue of bamb elements and surface materials, soil and water, made redioactive by eacconmpanyins radiations , fields. Debris is sucked high into the atzosvhere by efter winds of the explosion. ‘here this radioactive debris will fall is a mejor pre-shot consideration end pricerily influences the decision to detonate a nuclear exploSion at a certain tine. The area over which radioactive debris is spread end the intensity of fall-out on the ground are deterzined by the yield of the explosion as well as by wind pattern since the larges the yield, the more surface cateriels ere sucked up iato the Cloud and the more fission fragments are aveaileble. The relee- tionship between yield and fall-out is knowm only qualitatively. 4. PRE-SHOT INFORMATION: The operational aspects of the BRAVO experience were planned and canceived in the lisht of experience geined fram previmsoperations. These factors were considered: a. The basis for forecasting where fallout will go is experience gained from overseas test operations CROSSROADS, SANDSTONE, GREENHOUSES and IVY and to a certain extent fron tests at the Nevada Provins Ground. Prior to the firing of BRAVO, only one megaton yield device (IVY-hIK=)-had beea detam ted. Although conscientious efforts were made to docusent the fal- out from MIKE, only about S% of the total debris could ever be accounted for. s The technique used for forecasting fallout pate terns is to consider the cloud as a small area source (abdout ea 15 mile radius); then add vectorially forecast winds fro= the surface to approxicately 100,000 feet. The next step is to outline an area on the ground where fallout is expected. Tis area is computed by taking into consideration particle size, diffusion into the atmosphere, wind pattern, yield and source radius. Such patterns have been largely confirmed by experi“ence in Nevada as well as by the meager data availabie here. _ be yal \ \ oe ~—~\ ’ me . oe . ” @ The surface redex was plotted, with an insuresce factor edded, 1.e., smaller particles then previous experiess indicated necessary were considered. This doubled distances from ground zerg wnere fallout was predicted to occur. @. The upwind intensity of radiation levels at vasious distances was considered to be of the same order of ragni= tude as for IVY-LIKEe. Radietion versus distence lines were transposed to Bikini Atoll. _" 2 pons Exes