Radioisotope Brief: Americium-241 (Am-241)

Half-life: 432.2 years

Mode of decay: Alpha particles and weak gamma radiation

Chemical properties: Crystalline metal that is solid under normal conditions. Am-241 can be combined with beryllium to produce neutrons.

What is it used for?

Am-241 is used in some medical diagnostic devices and in a variety of industrial and commercial devices that measure density and thickness. Tiny Am-241 sources are also present in smoke detectors.

Where does it come from?

Am-241 is a manmade metal that is produced from plutonium. Am-241 found in the environment is the result of past nuclear weapons testing.

What form is it in?

Am-241 found in the environment is in the form of microscopic dust. Am-241 used in industrial, medical, or commercial devices is in the form of coin-sized metal or plastic discs. The Am-241 source present in a smoke detector is inside a metal cylinder that is about the size of a pencil erasure.

What does it look like?

Am-241 is a silver-white metal that is solid under normal conditions.

How can it hurt me?

As a dust or fine powder, Am-241 can cause certain cancers. When Am-241 powder is swallowed, absorbed through a wound, or inhaled it can stay in the body for decades. Am-241 concentrates in the bones, liver, and muscles, exposing these organs to alpha particles.

For more information about Am-241, see the Public Health Statement by the Agency for Toxic Substances and Disease Registry at http://www.atsdr.cdc.gov/toxpro2.html, or visit the Environmental Protection Agency at http://www.epa.gov/rpdweb00/radionuclides/americium.html.

To learn more about the use of radioactive materials in smoke detectors, visit the Environmental Protection Agency web site at http://www.epa.gov/radiation/sources/smoke_alarm.htm.

For more information on protecting yourself before or during a radiologic emergency, see CDC’s fact sheet titled “Frequently Asked Questions (FAQs) About a Radiation Emergency” at emergency.cdc.gov/radiation/emergencyfaq.asp, and “Sheltering in Place During a Radiation Emergency,” at emergency.cdc.gov/radiation/shelter.asp.

For information about possible countermeasures for internal contamination with Am-241, please see CDC's fact sheet on DTPA.

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