0018933 field program since radiation intensity mezauremexts must be made cver . areas up totes of thousands of square milez, . When the fxllout is deposited mainly over the surfsce of the ocean, the origina! pattarns are fistorted continuously by settling of the particles and by osesz2 carrenta, The collec- tion of samples at the earth's surface which are truly representative of the areca sampled and free from collecter bias presents problema which have not been fully solved to dzte, oo, \ Le Cenversion of gemma intensity contour data te fraction of device requires knowledge of the relation of dose rate te fizsions per unit area of the fallout field at cne hour and of the gross radioactive decay rate, The decay rate varies with the device composition, environment and fractienation in a way which is not well understeod, Some urcertsinty will always be presentin local fallout determinations by this method when fractHonztion exists to an unknown degree, even though all the other quantities are known accuratelys Ancther procedure for the determination cf fallout partition was originated by the University cf California Radiztion Laberztory bzsed on she supposition that certain cf the rare gas fission products remzin througheut ihsir lifetimes as free atoms unetteched to surfaces (Reference 26), If this is true, they will net be rermoved frem the cloud by the falling particles and may be considered as representative of the number of fivzions remzin- 25