GAMMA DOSE RATES AT RONGELAP ATOLL, 1954~1963 INTRODUCTION Rongelap Atoll, Marshall Islands, was accidentally con- taminated on March 1, 1954 with radioactive fallout from a thermonuclear device detonated at Bikini Atoll some 80 miles to the west. Eighty-two natives residing on Rongelap Island were evacuated and repatriated in June 1957. The atoll, its inhabitants and its economy have been briefly characterized‘? , The decline of gamma dose rates resulting from the fallout is discussed in this report. RESULTS Dose rates on D + 1 Gamma dose rates at Rongelap Atoll on D + 1 (time of detonation plus one day) were estimated to be 3.5 r per hour at the inhabited islet of Rongelap in the south and 35 r per hour at uninhabited Lomuilal islet in the northern part of the atoi 2) , Fig. 1. These estimates were based on extra- polations of measurements made two days after initial fallout '?) , The subsequent decline of gamma dose rates, based on survey meter readings taken three feet above the ground at Rongelap : 3 and Kabelle islets, is compared with the theoretical decay‘ )