ARPANSA - Australian Radiation Protection and Nuclear Safety Agency

Basic facts

Symbol:	241Am or Americium-241
Atomic Number:	95
Mass Number:	241
Half Life:	432.2 years
Decay Mode:	Emits high energy alpha particles and low energy gamma rays to decay to a more stable isotope of neptunium-237.

History

Americium-241 was discovered in 1944 by Dr. Glenn Seaborg and his colleagues at the University of Chicago. Americium is a radioactive element in all its isotopic forms. It was named after the continent of America.

How is it produced?

Americium-241 is not found naturally in the environment. It is artificially produced in commercial quantities in a nuclear reactor as a result of the neutron bombardment of plutonium. Plutonium-239 absorbs two neutrons to become plutonium-241 which then decays by emitting beta particle radiation to become americium-241. Americium is produced overseas where there are suitable facilities available. Only a few kilograms of americium-241 are produced worldwide each year.

Americium is also produced in the fallout from the detonation of nuclear weapons containing plutonium. There is americium-241 contamination in small areas in Australia as a result of British, American and French nuclear weapons testing. British testing in Maralinga and Emu in South Australia, and the Monte Bello Islands off the coast of Western Australia resulted in soil contamination of americium-241. There has since been a major clean-up of radioactive materials conducted by ARL (now known as ARPANSA).

Where is it found in Australia?

Smoke detectors

Americium is used as the active element in domestic smoke detectors. The americium is present in the form of fine particles rolled into a metallic foil. In this form it cannot be suspended in air and inhaled.

In Australia, individual smoke detectors can be discarded in household garbage. The amount of americium-241 in a single smoke detector is negligible compared with the natural radioactivity in one cubic metre of soil. In addition, due to the construction of these detectors the americium is highly immobile in the environment, so the associated environmental risks are very low

Nuclear weapons fallout

Americium-241 can be found as fallout from detonation of nuclear weapons containing plutonium. Due to atmospheric testing of nuclear weapons in the southern hemisphere in the past, americium-241 may be present in Australian soils in trace amounts.

What is it used for in Australia?

The main use for americium-241 in Australia is in household and industrial smoke detectors. One gram of americium-241 provides enough radioactive material for 5000 smoke detectors.

A typical smoke detector contains an ionisation chamber which uses the alpha radiation from americium-241 to detect smoke in the air. Since alpha particles can only penetrate a few millionths of a metre (microns) in solid matter, very few of the alpha particles escape from the casing of the smoke-detector; those that do escape are absorbed by a few centimetres of air. There is also a small amount of gamma radiation present at low energies that poses no risk to occupants of a household. More information about the Radioactivity in Domestic Smoke Alarms is available on the ARPANSA webpage.

Americium-241 has a few other commercial uses within Australia. These utilise the low-energy gamma rays emitted. Americium is used in brachytherapy, a treatment in which americium-241 pellets are placed in the body for cancer treatment. It is also used in scientific and medical research. Americium-241 coupled with caesium-137 is used in fluid density gauges. A mixture of americium-241 and beryllium is used in industrial soil moisture-sensing gauges, pavement density gauges, gauges that detect the thickness of paper, glass and metal foil, as well as being used in a device that detects lead levels in paint. Americium-241 also has a use in fluid level gauges, such as the ones employed in some aircraft fuel gauges.

What are the health effects?

Americium-241 presents a danger if it is taken into the body through ingestion, inhalation or through open wounds. It emits alpha radiation which does not present an external risk as the radiation is absorbed by the dead layer of human skin without causing any harm. It also emits a small amount of low-energy gamma radiation.

Large amounts of americium-241 taken into the body from contaminated soil could pose a risk to health. It can concentrate in the liver, muscles and the skeleton where it can stay in the body for decades exposing surrounding bone and tissues to both alpha and gamma radiation, increasing the risk of developing cancer. There is an extremely low chance of any member of the Australian public being exposed to dangerous levels of americium-241.

The americium-241 present in a household smoke detector is in oxide form, and is highly insoluble. If the americium from a smoke detector was swallowed it would pose very little risk of radiation-related health effects because it is not readily absorbed by the body. If a smoke detector is burned in a house fire and the americium source melts, it still poses essentially no risk as the heat from a house fire is not enough to vaporise the americium and create an inhalation hazard.

Under normal circumstances, there is no risk of adverse health effects due to the use of americium-241 in smoke detectors or the disposal of individual units in household garbage. This is because the amount of alpha-emitting radioactivity in a cubic metre of normal soil is generally at least 12 times as much as the alpha emitting radioactivity present in a smoke detector.

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