Background gamma radiation and soil activity measurements in the northern Marshall Islands.

We report on measurements of external gamma radiation on 9 islands in 4 atolls in the northern Marshall Islands, all of which were affected by the US nuclear testing program from 1946 to 1958 (Enjebi, Ikuren, and Japtan in Enewetak Atoll; Bikini and Enyu in Bikini Atoll; Naen in Rongelap Atoll; and Aon, Elluk, and Utirik in Utirik Atoll). We also report americium-241, cesium-137, plutonium-238, and plutonium-239,240 activity concentrations in the soil samples for 11 islands in 4 northern atolls (Enewetak, Japtan, Medren, and Runit in Enewetak Atoll; Bikini and Enyu in Bikini Atoll; Naen and Rongelap in Rongelap Atoll; and Aon, Elluk, and Utirik in Utirik Atoll) and from Majuro Island, Majuro Atoll in the southern Marshall Islands. Our results show low external gamma radiation levels on some islands in the Enewetak Atoll and Utirik Atoll, and elevated levels on Enjebi Island in the Enewetak Atoll, on Bikini Atoll, and on Naen Island in the Rongelap Atoll.

Radiation maps of ocean sediment from the Castle Bravo crater.

On March 1, 1954, the United States conducted its largest thermonuclear weapon test in Bikini Atoll in the Marshall Islands; the detonation was code-named "Castle Bravo." Radioactive deposits in the ocean sediment at the bomb crater are widespread and high levels of contamination remain today. One hundred thirty cores were collected from the top 25 cm of surface sediment at ocean depths approaching 60 m over a ∼2-km area, allowing for a presentation of radiation maps of the Bravo crater site.

In situ measurement of cesium-137 contamination in fruits from the northern Marshall Islands.

Radioactive contamination of fruits in the northern Marshall Islands, resulting from the US nuclear weapons testing program in the 1940s and 1950s, is still a human health concern, in particular pertaining to island population resettlement and the economic benefit from farming. Over 200 fruits, primarily coconuts and pandanus, were collected on 11 islands from four atolls in the northern Marshall Islands in 2017. The energy spectra from nuclear gamma decays were measured on a research vessel for each fruit in situ.