Americium (chemical symbol Am) is a man-made radioactive metal,
with Atomic Number 95. The most important isotope of Americium
is Am-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?
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
research
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.
But, 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.
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 it 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. Also, when household smoke detectors are
discarded, they go directly to municipal landfills, including
any Am-241 they may contain.
*While most of the shorter-lived radionuclides have now decayed
away, longer-lived radionuclides such as americium-241 will remain
in the environment for many years. However, since they decay slowly,
they emit radiation slowly, so the dose is very low and will decline.
In 1987, the National Council on Radiation Protection and Measurements
estimated that the combined annual effective dose equivalent to
an individual from the radionuclides remaining is less than one
mrem per year. Details of the study are reported in NCRP Report
No. 93, Ionizing Radiation
Exposure of the Population of the United States.
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
check with your local fire department for safe disposal procedures.
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.
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.
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 and disposed of according to manufacturers'
instructions. However, 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.
You need specialized equipment to detect the presence of Am-241.
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.
