Measurement of background gamma radiation in the northern Marshall Islands

We report measurements of background gamma radiation levels on six islands in the northern Marshall Islands Enewetak, Medren, and Runit onEnewetak Atoll; Bikini and Nam on Bikini Atoll; and Rongelap on Rongelap Atoll). Measurable excess radiation could be expected from the decay of Cs-137 produced by the US nuclear testing program there from 1946 to 1958. These recordings are of relevance to safety of human habitation and resettlement. We find low levels of gamma radiation for the settled island of Enewetak [mean = 7.6 millirem/year mrem/y) = 0.076 millisievert/year mSv/y)], larger levels of gamma radiation for the island of Rongelap mean = 19.8 mrem/y = 0.198 mSv/y), and relatively high gamma radiation on the island of Bikini mean = 184 mrem/y = 1.84 mSv/y). Distributions of gamma radiation levels are provided, and hot spots are discussed. We provide interpolated maps for four islands Enewetak, Medren, Bikini, and Rongelap), and make comparisons to control measurements performed on the island of Majuro in the southern Marshall Islands, measurements made in Central Park in New York City, and the standard agreed upon by the United States and the Republic of the Marshall Islands RMI) governments 100 mrem/y = 1 mSv/y). External gamma radiation levels on Bikini Island significantly exceed this standard P = << 0.01), and external gamma radiation levels on the other islands are below the standard. To determine conclusively whether these islands are safe for habitation, radiation exposure through additional pathways such as food ingestion must be considered.