National Cancer Institute U.S. National Institutes of Healthwww.cancer.gov
National Cancer Institute Radioactive I-131 from Fallout

Summary Information

During the 1950s and 1960s, the U.S. government conducted approximately 100 above-ground nuclear bomb tests at the Nevada Test Site (NTS). After 1962, all tests at the NTS were conducted underground. All above-ground tests and a limited number of underground tests conducted before 1971 released a number of radioiodines, including Iodine-131 (I-131), into the atmosphere. Because I-131 accumulates in the thyroid gland, concerns have been raised that the fallout could cause thyroid cancer in people who were exposed to it especially if they were children at the time of exposure.

Every American living in the continental United States received varying levels of I-131 for about two months following each test. The thyroid dose depends largely on age at the time of each test, geographic location, and the type and amount of milk consumed.

People living outside the continental United States also received radiation exposures resulting from I-131 released from the NTS; the radiation exposures received by those people have not been estimated, as they are believed to be much smaller than those received within the continental United States.

In conjunction with a nationwide education campaign to inform Americans about this exposure, the National Cancer Institute (NCI) has developed this tool to help Americans estimate individual thyroid dose from I-131 released from the NTS.

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