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Radioactive Fallout From Nuclear Weapons Testing

Radiation Facts

  • After a nuclear explosion, debris and soil can mix with radionuclides. This mixture is sent up into the air and then falls back to Earth. It is called fallout and it typically contains hundreds of different radionuclides.
  • Since the conclusion of the weapons testing in the 1980s, radionuclides in the atmosphere have largely decayed away.

Detonating nuclear weapons above ground sends radioactive materials as high as 50 miles into the atmosphere. Large particles fall to the ground near the explosion-site, but lighter particles and gases travel into the upper atmosphere. The particles that are swept up into the atmosphere and fall back down to Earth are called fallout. Fallout can circulate around the world for years until it gradually falls down to Earth or is brought back to the surface by precipitation. The path of the fallout depends on wind and weather patterns.

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About Radioactive Fallout From Nuclear Weapons Testing

Fallout typically contains hundreds of different radionuclides. Some stay in the environment for a long time because they have long half-lives, like cesium-137, which has a half-life of 30.17 years. Some have very short half-lives and decay away in a few minutes or a few days, like iodine-131, which has a half-life of 8 days. Very little radioactivity from weapons testing in the 1950s and 1960s can still be detected in the environment now.

The United States conducted the first above-ground nuclear weapon test in southeastern New Mexico on July 16, 1945. Between 1945 and 1963, hundreds of above-ground blasts took place around the world. Over time the number and size (or yield) of these blasts increased, especially in the late 1950s and early 1960s. After the Limited Test Ban Treaty of 1963 was signed by the United States, the Soviet Union and Great Britain, most above-ground blasts ceased. Some above-ground weapons testing by other countries continued until 1980. Since the end of above-ground nuclear weapons testing, the day-to-day radiation in air readings from monitoring sites has fallen. For many years, analysis of air samples has shown risk levels far below regulatory limits. In fact, results are now generally below-levels that instruments can detect.

The EPA maintains a system of radiation monitors throughout the United States. These monitors were originally designed to detect radionuclides that were released after a nuclear weapon detonation. Now, the EPA uses this system, called RadNet, to look at background radiation levels at many locations across the United States. Background radiation is around us all the time, mostly from natural sources, like naturally-occurring radon and uranium. For more information about the history of RadNet, please visit the Learn About RadNet webpage.

Some of the fallout radionuclides the EPA’s monitoring systems may detect include:

Even though there is very little fallout that still exists in the environment, it is important to remember that fallout can be very dangerous. This section talks about the different ways we can be exposed to radiation if a nuclear detonation occurs.

When a nuclear detonation occurs, people, plants, and animals can be exposed to the fallout in several ways. Livestock may eat contaminated plants or drink contaminated water. People who then eat this livestock will then still experience internal contamination, in which radioactive material ends up inside of our bodies, despite not consuming contaminated plants or water directly.

Radionuclides that are inhaled or ingested are not blocked by an external shield. These radionuclides interact with internal cells and tissues, which increases the risk of harmful health effects. When radionuclides are ingested, they can change the structure of cells, which is one of the ways people can develop cancer. 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 1961. This is one of the reasons why radiation protection professionals work hard to protect people from unnecessary exposure to radiation.

The radioactive dust that settles on the environment around us is an example of potential external exposure. Radionuclides that emit alpha and beta particles would pose a lower external exposure threat because they do not travel very far in the atmosphere and are not as penetrating as more energetic radiation. Shielding, one of the three principles of radiation protection, prevents some external exposure because alpha particles are blocked by the dead skin cells that sit on the surface of our bodies. Gamma rays, however, travel much farther in the atmosphere, and are higher energy rays that can only be blocked by heavy shielding, like a concrete wall or a lead apron. These rays pose a higher external exposure risk.

Alpha particles come from the decay of the heaviest radioactive elements, such as uranium, radium and polonium. 

Beta-emitters are most hazardous when they are inhaled or swallowed.

Gamma rays are often emitted along with alpha or beta particles during radioactive decay.

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