Nuclear Weapons Tests and Fallout Exposure

Between 1945 and 1980, the U.S., the former Soviet Union., the U.K., France, and China carried out more than 500 atmospheric tests of nuclear weapons totaling the explosive equivalent of 440 megatons of TNT. These tests released radioactive material into the atmosphere, much of which became widely dispersed before being deposited as fallout. Cancer investigators have been studying the health effects of exposure to radiation for decades, including the exposure from radioactive fallout, making radiation a well-understood agent of environmental injury. The legacy of open-air nuclear weapons testing includes a small increase in thyroid cancer, leukemia, and certain solid tumors.

The Nevada Test Site (NTS) in the U.S. was used for surface and above-ground nuclear testing from early 1951 through mid-1962. More than 100 tests were conducted at or above ground level and hundreds underground, Radioactive debris from the NTS tests subsequently was deposited, to varying degrees, over most of the continental U.S.

Global fallout originated from high-yield weapons that derived much of their yield from fusion reactions. These tests were conducted on hydrogen bombs (known as H-bombs) by the U.S. in the mid-Pacific and by the Soviet Union at northern latitudes. Fallout from these large tests was distributed over the northern hemisphere.

Thyroid Cancer Risk from Fallout

Fallout from the NTS and from global sources contributed exposures to persons living in the U.S. through ingestion of contaminated food products, primarily fresh milk, but also from external dose and from inhalation. The internal thyroid dose received by any individual depends largely on the individual’s age at the time of each test, geographic location, and the types and amounts of fresh milk consumed. The principal radionuclide of concern for internal dose to the thyroid gland is Iodine-131 (I-131). There are many other radionuclides deposited in fallout though they primarily contribute to the thyroid dose from external exposure.

About the I-131 Calculator

The NCI Thyroid Dose and Risk Calculator for Nuclear Weapons Fallout for the U.S. Population (NCI Fallout Calculator) is a software tool to estimate the internal and external dose to thyroid gland from exposure to radioactive fallout and the subsequent risk of developing thyroid cancer for persons resident in the U.S. between 1951 and 1980. However, because gamma radiation from external dose is of high enough energy to be deeply penetrating, the external dose to the thyroid can also be an estimate of external dose to all other organs including active bone marrow. Estimated thyroid dose from nuclear weapons testing to persons born after 1982 is negligibly small and thus the calculator is not relevant in these circumstances.

Scientists wishing to use the data upon which the calculator is based for their research projects may request it, in writing, with an email to Dr. Choonsik Lee.

For additional information, see Get the Facts about Exposure to I-131 Radiation.

This version of the fallout dose and risk calculator was released in February 2024. Please refer to upgrade record for the Individual Thyroid Risk and Dose calculator for fallout for a history of changes to the fallout calculator.

References and Related Links

• Estimated Exposure and Thyroid Doses Report, (PDF, 8 MB). NCI Report 1997.
• Exposure of the American People to Iodine-131 from Nevada Nuclear-Bomb Tests, National Academies Press, 1999
• Simon, SL, Bouville A, Land CE. Fallout from nuclear weapons tests and cancer risks. Exposures 50 years ago still have implications today that will continue into the future, (PDF, 4 MB). Am Sci. 2006.
• Veiga LHS, et al. Thyroid cancer after childhood exposure to external radiation: an updated pooled analysis of 12 studies, Radiation Research. 2016.
• Brenner AV, et al. I-131 dose response for incident thyroid cancers in Ukraine related to the Chornobyl accident. Environ Health Perspect. 2011.
• NCI Methodologic Studies of Radioactive Fallout

Acknowledgements

The original dose calculator was developed by Jed Rifkin, Ph.D., and two investigators formerly at the NCI, Andre Bouville, Ph.D., and Steven L. Simon, Ph.D. Dr. Simon led the effort to update the tool with assistance from Dr. Bouville, the Oak Ridge Center for Risk Analysis (formerly SENES Oak Ridge, Inc.), and Mr. Harold Beck.

Choonsik Lee, Ph.D., Dosimetry Unit Head and senior investigator in the Radiation Epidemiology Branch, oversees maintenance of the calculator.

Support for updates was provided by the National Institutes of Allergies and Infectious Diseases (NIAID), Radiation Countermeasures Program through an intra-agency agreement (NIAID agreement #Y2-Al-5077 and NCI agreement #Y3-CO-5117).