ATOLL SOIL TYPES IN RELATION TO THE DISTRIBUTION OF FALLOUT RADIONUCLIDES INTRODUCTION The redistribution of radionuclides in atoll soils following contamination with radioactive fallout is the subject paper. of this Rongelap Atoll, northern Marshall Islands, in the central Pacific Ocean, presents a unique opportunity for such studies since it was substantially contaminated with radioactive fallout only once. The fallout resulted from a thermonuclear device detonated at Bikini Atoll eighty miles to the west on March l, 1954. Although there was some additional contamination from nuclear tests in 1956 and 1958 the total contribution of radionuclides from the fallout of these subsequent test series amounted to a fraction of one per cent of the amount from the 1954 fallout. Gamma radiation dose rates at Rongelap at detonation plus one day ranged from 3.5 r/hr at the southern islets of the atoll to 35 r/hr at the northern islets (Dunning 1957). ‘These rates declined at approximately the rate pre- dicted for mixed fission products by Miller and Loeb (1958). Rongelap Atoll has a lagoon area of 388 square miles and an average depth of 168 feet (Nugent 1946, p. 748). The emer- gent land area is about three square miles, .consisting of “*% Lee.