Americium-241 - UW-L Brachy Course

Relevant historical data:

First produced in 1944 during the Manhattan Project at the University of Chicago's Metallurgical Labratory by bombarding plutonium with neutrons. Created by bombarding Plutonium-239 with high energy neutrons to create Plutonium-240. Plutonium-240 is bombarded with high energy neutrons to create Plutonium-241 which then decays to Am-241 through beta decay. Am-241 did not receive a name until 1946 in honor of the continent where it was discovered.

Chemical/Radioactive Composition:

Specific Activity = 3.5 Ci/g
Atomic number = 95
Physical appearance = silver metal that tarnishes slowly in air and is soluble in acid.
AmO2 = Americium oxide

Energy Characteristics:

Decays by alpha, beta and gamma emissions.
Alpha=5.49 and 5.44 MeV
Gamma emissions=0.0595 and 0.0263 MeV
Beta=0.052 MeV
Am-241 will decay to Neptunium-237

Exposure Rate Constant:

0.122 R cm^2 mCi^-1 hr^-1
Air kerma = 0.107 cGy cm^2 mCi^-1 hr^-1

Half-life Properties:

The unstable version of Am-241 has a half life of 432.2 years while the stable version of Am-243 has a half life of 7500 years.

Biological half-life of Am-241 following injestion or inhalation is 50 years in bone, 20 years in liver, and permanent in gonadal tissue.

Forms available for use:

For sale by US Atomic Energy Commission for $1,500/gram in the form of AmO2. AmO2 is used in the production of smoke detectors. When combined with beryllium, Americium can be used as a neutron source for testing of machinery and equipment or as a thickness gauge in the glass industry.

HVL in lead:

0.12 mm Lead


Approximately 1 micro Ci is present in household smoke detectors and up to 50 micro Ci in industrial smoke detectors. The NRC holds individuals as exempt from licensing in order to own a smoke detector as the amount of radiation is so small. In addition, smoke detectors are allowed to be disposed of in normal trash.

Used in formula/calculation:

1 micro Ci = ? mgRaeq
1 micro Ci = 0.001 mCi x (0.122/8.25) =

Uses in Radiation Oncology:

Not commercially available. In the prototype stage. (1993) Was used for transportable radiology functions.

Treatment Planning:

0.1 to 10.0 Ci produced for prototype.

One other interesting fact:

Am-241 is of concern due to its availabilty and the possible use in a dirty bomb.



Argonne National Labratory, EVS. Human Health Fact Sheet, August 2005.
CDC - Centers for Disease Control - Radioisotope Brief. August 18th, 2004.
MSDS - Material Safety Data Sheet
Radioactive Consumer Products - Oakridge Associated Universities. 1999.
NTI - Nuclear Threat Initiative - Illicit Trafficking and Radiological Terrorism. July 12, 2007.
Washington State Department of Health - Division of Environmental Health - last updated 6/1/07.
EPA - Radiation Protection

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