— 0018933 field program since radiation intensity measurements must be made over areas up to tensof thousands of square miles, When the fallout is deposited mainly over the surface of the ocean, the original patterns are distorted continuously by settling of the particles and by ocean currents, The collec- tion of samples at the earth's surface which are truly representative of the area sampled and free from collector bias presents problems which have not been fully solved to date, Conversion of gammaintensity contour data to fraction of device requires knowledge of the relation of dose rate to fissions per unit area of the fallout field at one hour and of the gross radioactive decay rate. | The decay rate varies with the device composition, environment and fractionation in a way which is not well understood. Some uncertainty will always be present in local fallout determinations by this method when fractionation exists to an unknown degree, even though all the other quantities are known accurately, Another procedure for the determination of fallout partition was originated by the University of California Radiation Laboratory based on the supposition that certain of the rare gas fission products remain throughout their lifetimes as free atoms unattached to surfaces (Reference 26), If this is true, they will not be removed from the cloud by the falling particles and may be considered as representative of the number of fissions remain- SAN BRUNO FRE 25 —_— ”—~—<‘(‘ér 25