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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, or visit the Environmental Protection Agency at

To learn more about the use of radioactive materials in smoke detectors, visit the Environmental Protection Agency web site at

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, and “Sheltering in Place During a Radiation Emergency,” at

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

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