Radioactive Fallout From Nuclear Weapons Testing
Detonating nuclear weapons above ground sends radioactive materials into the atmosphere from the
ground level up to very high elevations.
Fallout typically contains hundreds of different radionuclides.
Since the end of aboveground nuclear weapons testing, radionuclides have largely decayed away.
About Radioactive Fallout From Nuclear Weapons Testing
Detonating nuclear weapons above ground sends radioactive
materials into the atmosphere from the ground level up to as high as
50 miles! Large particles fall back near the explosion site, but lighter
particles and gases travel into the upper atmosphere. They can
circulate around the world for years, or even decades, until they
gradually settle out or are brought back to the surface by
precipitation. The height and spread of fallout depends on such
factors as the type of weapon and weather patterns. Fallout typically
contains hundreds of different radionuclides. Some stay in the
environment for a long time because they have long half-lives.
Some have very short half-lives and decay away in a few minutes or
a few years. Certain radionuclides produce high levels of radiation.
Both are potential risks to human health and the environment.
However, very little radioactivity from weapons testing in the 1950s
and 1960s can even be detected in the environment now.
Some of the fallout radionuclides detected by EPA's monitoring
systems include:
Americium-24f.
Cesium-137N.
lodine-131iN.
Strontium-90iv.
When there is a nuclear detonation, people and other living things
can be exposed to fallout through several pathways. External or
direct exposure would come from fallout on the ground. Internal
exposure would occur if radioactive particles were inhaled or
ingested (swallowed). Ingestion would occur by eating contaminated
crops or meat from livestock that had eaten contaminated plants.
Radionuclides that emit alpha and beta particles would pose a lower external exposure threat because they
don't travel very far in the atmosphere and are not as penetrating as more energetic radiation. For example,
alpha particles can be stopped by the dead cells on the skin's surface. However, gamma rays travel much
Above-Ground Nuclear Test conducted at
the Nevada Test Site on May 25, 1953
(Source: Nevada Department of
Environmental Protection)
United States Environmental Protection Agency | Office of Radiation and Indoor Air (6608T) | EPA 402-F-14-002 | August 2014 | p. 1
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farther in the atmosphere and can penetrate the body. They pose a much higher external exposure risk.
Radionuclides that are inhaled or ingested would continue to emit radiation directly to living tissue, increasing
the risk of harmful health effects such as cancer, caused by damage to DMA in the cells. The health risks from
fallout have been described in many studies. One example is the Federal Radiation Council's 1962 report
"health implications of fallout from nuclear weapons testing through 1961V
The U.S. conducted the first aboveground nuclear weapon test in southeastern New Mexico on July 16, 1945.
Between 1945 and 1963, hundreds of aboveground blasts took place around the world. The number and size
(yield) of blasts increased, particularly in the late 1950s and early 1960s. Following the signing of the Limited
Test Ban Treaty of 1963 by the United States, the Soviet Union and Great Britain, most aboveground blasts
ceased. Some above-ground weapons testing by other countries continued until 1980. Since the end of
aboveground nuclear weapons testing, the day-to-day readings from radiation monitoring sites have fallen. For
many years, analysis of typical samples shows risk levels far below regulatory limits. In fact, results are now
generally below levels that instruments can detect.
Rules and Guidance
The main documents that govern nuclear weapons testing are treaties. There are three main treaties:
THE TREATY ON THE LIMITATION OF UNDERGROUND NUCLEAR WEAPON TESTSvi
This treaty is also known as the Threshold Test Ban Treaty. It was signed in July of 1974 by the United States
and the Union of Soviet Socialist Republics (USSR). It established a nuclear "threshold," by prohibiting test
having a yield exceeding 150 kilotons (equal to 150 tons of TNT).
TREATY BANNING NUCLEAR WEAPON TESTS IN THE ATMOSPHERE, IN OUTER SPACE AND UNDER
WATERvii
The Test Ban Treaty of 1963 prohibits nuclear weapons tests "or any other nuclear explosion" in the
atmosphere, in outer space and under water. It does not ban tests underground. The goal of the treaty is to
end radioactive contamination of the environment.
NUCLEAR-TEST-BAN TREATY
The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is a legally binding globalban on nuclear explosive
testing. The CTBT was opened for signature in 1996. The United States has signed the treaty but it has not
been ratified by the Senate.
What you can do
There is very little fallout left from nuclear weapons testing that occurred in the 20th century. Most of what is
left decays very slowly and therefore gives off little radiation.
Where to learn more
You can learn more about radioactive fallout from nuclear weapons testing by visiting the resources available
on the following webpage: http://www.epa.gov/radtown/fallout-nuclear-weapons-testing.htmltflearn-more.
' http://www.epa.gov/radiation/radionuclides/americium.html
" http://www.epa.gov/radiation/radionuclides/cesium.html
"' http://www.epa.gov/radiation/radionuclides/iodine.html
iv http://www.epa.gov/radiation/radionuclides/strontium.html
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v http://www.epa.gov/rpdwebOO/docs/federal/frc rpt3.pdf (13 pp, 350 K About PDF)
vi http://www.state.goV/t/isn/5204.htm
vii http://www.state.gOv/t/isn/4797.htm
viii http://www.state.goV/t/avc/c42328.htm
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