Americium (chemical symbol Am) is a man-made radioactive metal, with Atomic Number 95. The most important isotope of Americium is Am-241.
On this page:
- Who discovered americium-241?
- Where does americium-241 come from?
- What are the properties of americium-241?
- What is americium-241 used for?
- How does americium-241 get into the environment?
- How does americium-241 change in the environment?
- How do people come in contact with americium-241?
- How does americium-241 get into the body?
- What does americium-241 do once it gets into the body?
- How can americium-241 affect people's health?
- Is there a medical test to determine exposure to americium-241?
- How do I know if I'm near americium-241?
- What can I do to protect myself and my family from americium-241?
- What is EPA doing about americium-241?
Who discovered americium?
Americium (isotope Am-241) was discovered by nuclear chemist Glenn Seaborg and his colleagues at the University of Chicago in 1944.
Where does americium-241 come from?
Americium is a man-made metal produced when plutonium atoms absorb neutrons in nuclear reactors and in nuclear weapons detonations. Americium has several different isotopes, all of which are radioactive. The most important isotope is Am-241.
What are the properties of americium-241?
Americium is a silver-white, crystalline metal that is solid under normal conditions. All isotopes of americium are radioactive. Americium-241 primarily emits alpha particles, but also emits gamma rays. A mixture of americium-241 and beryllium emits neutrons. Americium-241 has a half-life of 432.7 years.
What is americium-241 used for?
By far the largest and most widespread use of americium-241 is as a component in household and industrial smoke detectors, where a small amount is used in an ionization chamber inside the detector.
Americium-241 is the only isotope of americium to have widespread commercial use. It is the radiation source for a number of applications:
- medical diagnostic devices
- fluid-density gauges
- thickness gauges
- aircraft fuel gauges
- distance-sensing devices, all of which utilize its gamma radiation.
A mixture of americium-241 and beryllium provides a neutron source for industrial devices that monitor product quality. Two examples are devices for nondestructive testing of machinery and gauges for measuring the thickness of glass and other products.
Exposure to Americium and Americium-241
How does americium-241 get into the environment?
Most americium-241 in the environment originates from the atmospheric testing of nuclear weapons during the 1950's and 1960's. The exposure to an individual from americium-241, and other long-lived radionuclides is very, very small. Facilities that produce weapons and manufacture smoke detectors are minor sources of Americium-241 contamination. Americium-241 may also enter the environment if industrial americium sources (many of which are portable) are lost or stolen, and subsequently broken open, or melted in a steel mill.
How does americium-241 change in the environment?
Americium-241 is an unstable (radioactive) isotope with a half-life of 432.7 years. As it decays, it releases alpha and gamma radiation and changes into neptunium-237, which is also radioactive. The americium-241 decay chain ends with bismuth-209, a stable (non-radioactive) element.
How do people come in contact with americium-241?
Exposure to any significant amount of Am-241 is unlikely under normal circumstances.
People may be directly exposed to gamma radiation from americium-241 by walking on contaminated land. They may also be exposed to both alpha and gamma radiation by breathing in americium contaminated dust, or drinking contaminated water. Because americium-241 was widely dispersed globally during the testing of nuclear weapons, only very minute amounts of it are found in the soil, plants, and water. Living near a weapons testing or production facility may increase your chance of exposure to americium-241.
Smoke detectors containing Am-241 also provide some radiation exposure. However, the radiation exposure people receive from a smoke detector is very low. The health risk reduction from the fire protection vastly outweighs the health risk from the radiation. That said, you should still handle smoke detectors containing americium with care. To avoid exposure:
- never dismantle a smoke detector
- never burn a smoke detector in your fireplace
The Nuclear Regulatory Commission, which regulates the radioactive material in smoke detectors, permits their disposal as ordinary trash.
How does americium-241 get into the body?
People who live or work near a contaminated site, such as a former weapons production facility, may ingest americium-241 with food and water, or may inhale it as part of resuspended dust.
What does americium-241 do once it gets into the body?
Once in the body, americium-241 tends to concentrate in the bone, liver, and muscle. It can stay in the body for decades and continue to expose the surrounding tissues to radiation, and increase your risk of developing cancer.
When inhaled, some Am-241 remains in the lungs, depending upon the particle size and the chemical form of the americium compound. The chemical forms that dissolve easily may pass into the bloodstream from the lungs. The chemical forms that dissolve less easily tend to remain in the lungs, or are coughed up through the lung's natural defense system, and swallowed. From the stomach swallowed americium may dissolve and pass into the bloodstream. However, undissolved material passes from the body through the feces.
Health Effects of Americium-241
How can americium-241 affect people's health?
Americium-241 poses a significant risk if ingested (swallowed) or inhaled. It can stay in the body for decades and continue to expose the surrounding tissues to both alpha and gamma radiation, increasing the risk of developing cancer. Americium-241 also poses a cancer risk to all organs of the body from direct external exposure to its gamma radiation. One source of direct exposure would be contaminated soil. Exposure to any significant amount of Am-241 is unlikely under normal circumstances. ("Normal circumstances" do not include trying to access or remove the Am-241 source in a smoke detector!)
Is there a medical test to determine exposure to americium-241?
Yes. There are tests that reliably measure the amount of americium in a urine sample, even at very low levels. Using these measurements, scientists can estimate the total amount of Am-241 present in the body. Other tests can measure Am-241 in soft tissues (such as body organs) and in feces, bone, and milk. None of these tests are routinely available in a doctor's office because they require special laboratory equipment.
Protecting People From Americium
How do I know if I'm near americium-241?
You need specialized equipment to detect the presence of Am-241.
What can I do to protect myself and my family from americium-241?
Most Americans never get close to a significant amount of Am-241, except in their household smoke detectors. Ionizing chamber smoke detectors contain a small amount of Am-241. Smoke detectors pose very little risk if used according to manufacturers' instructions.
You can follow some precautions to protect yourself and your family:
- Never try to access or remove the Am-241 source in your smoke detector.
- Be aware that industrial instruments using Am-241 can be lost, stolen, or otherwise fall out of monitored control. These "orphan sources" present a significant risk to those who come in contact with them. EPA, other federal, state and industry organizations are working together to locate and retrieve orphan sources throughout the U.S.
The Nuclear Regulatory Commission regulates the radioactive materials in smoke detectors. Because the amount of americium in these devices is so small, NRC's regulations exempt individuals purchasing smoke detectors from licensing requirements including those related to disposal of radioactive materials. You can dispose of single, household smoke detectors as ordinary trash.
What is EPA doing about americium-241?
Americium-241 in drinking water is covered under the Safe Drinking Water Act. This law establishes Maximum Contaminant Levels, or MCLs, for radionuclides and other contaminants in drinking water. The MCL for alpha particle activity applies to Am-241. The limit is 15 pCi/l alpha particle activity in drinking water.
EPA standards under the Clean Air Act limit Am-241 in the air. In addition, the cleanup of contaminated sites to be released for public use, must meet EPA's risk-based criteria for soil and ground water. For sites with residual Am-241 on the ground, EPA's cleanup standards set the potential cancer risk as being no more than a 1-in-10,000 to a 1-in-1,000,000 increased chance of developing cancer.
- Estimating Risk
Describes how EPA uses a combination of existing data and mathematical calculations (models) to estimate effects under a variety of conditions.