GAMMA DOSE RATES AT RONGELAP ATOLL, 1954-1963 INTRODUCTION Rongelap Atoll, taminated on March 1, Marshall Islands, was accidentally con- 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 : é 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 atoll (2) , Fig. 1. These estimates were based on extra- polations of measurements made two days after initial fallout ‘2? , The subsequent decline of gamma dose rates, based on survey meter readings taken three feet above the ground at Rongelap and Kabelle islets, is compared with the: theoretical decay '?? 1