and the decline of gamma dose rates will be more rapid. fore, in the future, There- long-range predictions of residual gamma dese rates based on the Rongelap experience would be likely to yield higher values than would actually occur. Fractionation of fallout In addition to the differences in composition of fallout from different devices and variations in measurements there is fractionation of the radionuclides, a change in species compositim with time or distance from origin. The various factors involved in fractionation are discussed in detail in the Congressional Hearings, 1959 (5) and with specific reference to the March 1, 1954 explosion in "The Effects of Nuclear Weapons,” 1962 "4 , Redistributionof fallout Reduction of gamma-dose rate levels due to redistribution of fallout possibly occurred during the first storm after fallout (Dunning, 1957), but thereafter redistribution had very little effect on the gamma dose rates Curing the first four years after fallout. The exception, of course, is the relatively rapid decline of radioactivity in the intertidal zone. Such rapid decline would also ve anticipated in areas in which there is heavy erosion. An example is the man-made erosion by bulldozers in the village area at Rongelap. The reduction of gamma dose rates following ood the storm could have been due to the washing of fallout material