Americium-241 is a silver-grey metal with two allotropic forms (alpha and beta, the transition from alpha to beta occurs at 1074°). It decays primarily by alpha particle emission to neptunium-237, which has a half-life of 2,144,000 years (it can also undergo spontaneous fission, but this is negligible - the branching ratio for this is 4 x 10^-10%). Low energy gamma radiation accompanies these decays, with the 59.5 keV gamma emission being of the most importance.

CHEMICAL, PHYSICAL, AND RADIOLOGICAL PROPERTIES

Important Compounds

Americium oxide (AmO2) Americium dioxide	23317-46-6 (12736-98-0)	black solid (m.p. >1000° (decomposes))	soluble in acids
Americium dioxide is the form in which americium is most likely to be encountered in a radiological dispersion device
Americium chloride (AmCl3) Americium trichloride	27388-85-8 (13464-46-5)	pink crystals (m.p. 715°)	soluble in water
Americium nitrate (Am(NO3)3) Americium trinitrate	56609-31-5 (25933-53-3)	Information not available	soluble in water
Americium nitrate solutions are commonly produced during recovery of americium from wastes
Americium-beryllium alloys	(178396-65-1)	Information not available	Usually in powder compacts
Used in neutron sources
CAS Registry Numbers in parentheses are for the compound without the specific radioisotope. These nonspecific compound registry numbers are useful for searches for general information on the compounds.

DETECTION

Radiation detectors will detect americium-241. Most detection will be based on detection of the 59.5 keV gamma.

Because of the very low penetration of alpha particles, the classic symptoms of radiation sickness in exposed individuals are unlikely to be a prompt indicator of americium-241 release. However, exposure to large quantities (e.g., more than 1 g) of americium-241 may result in significant exposure to gamma radiation.

SYMPTOMS AND EFFECTS

Americium-241 will be detectable in urine after exposure; direct in-vivo measurement is also possible with specialized equipment.

Americium's radiotoxic effects overwhelm any chemical toxicity.

Primary hazards due to americium-241 are prompt radiation injuries from exposures to large quantities (likely to be rare) and radiation-induced cancers due to long term exposure.

Classic radiation sickness is not likely with a release of americium-241 alone unless a victim is exposed to extremely large amounts. The agent may be released in combination with other radioisotopes which may induce radiation sickness.

Initial symptoms of radiation sickness may include:

• weakness
• anorexia
• vomiting
• diarrhea

These symptoms are followed after a latent period by the symptoms of the major radiation sickness syndromes, which are discussed in greater detail in the Radiation Sickness document.

Primary deposition sites for americium-241 are bone and liver.

MEDICAL COUNTERMEASURES

Useful Drugs	Ca-DTPA	Zn-DTPA

Treatment for exposure is based on mechanical removal of all possible agent and chelation.

Decontamination (removing clothing and showering) should be accomplished as soon after exposure as possible to minimize uptake of the material. In addition, nasal passages should be irrigated gently using saline or water.

If exposure was by ingestion, immediate administration of activated charcoal (50-100 g) may be helpful.

Enemas and laxatives may also be useful in speeding passage of the material through the gastrointestinal tract.

Trisodium calcium diethylenetriaminepentacetate (Ca-DTPA) and trisodium zinc diethylenetriaminepentacetate (Zn-DTPA) are chelating agents which may be used to reduce the body burden of americium. The recommended initial dose for both agents is 1 gram (14 mg/kg up to 1 gram in children), with a subsequent maintenance dose in the same amount (adults 1 g; children 14 mg/kg up to 1g) given every day afterwards until monitoring indicates that the americium has been adequately cleared. The preferred route of administration is intravenous (slow push of the dose in 5 mL of solution over 3 to 4 minutes or in 100-250 mL of Ringer's lactate, normal saline, or 5% dextrose in water by IV infusion over 30 minutes).

Unless the victim is pregnant, Ca-DTPA should be used for treatment during the first 24 hours post-exposure, as it seems to be more effective than Zn-DTPA during this period. Zn-DTPA should be used exclusively when victims are pregnant, and is preferred for use after the initial 24 hours after exposure. When Ca-DTPA must be used for maintenance for longer than 24 hours post-exposure, zinc supplements should be given.

! Use only Zn-DTPA for pregnant victims if possible.

Victims should be encouraged to drink fluids to promote excretion, and to urinate frequently to minimize exposure of the bladder to radiation.

PHYSICAL COUNTERMEASURES

Initial evacuation distance should be at least 100 meters (330 feet).

Protective equipment (self-contained breathing equipment or mask suitable for prevention of particculate inhalation, barrier suit) must be used by those entering the contaminated area.

Also refer to 2004 Emergency Response Guidebook (ERG2004) Guide 161.

Because of the poor penetrating power of alpha radiation, prompt decontamination of exposed individuals can significantly reduce risk. Decontamination is accomplished by removing clothing (which may be bagged for subsequent evaluation and possible return to victims) and washing of victims.

Medical personnel treating casualties should wear at least masks and barrier clothing appropriate for Universal Precautions cases; medical personnel using this level of protection will usually also need to undergo decontamination on completion of their patient treatment tasks.

More elaborate anticontamination suits may eliminate the need for individual decontamination of medical personnel.

Procedures for decontamination of physical facilities and equipment will depend on the physical and chemical form of the agent disseminated but will be based on the collection of the agent and contaminated materials and their disposal in appropriate areas.

COMMENTS

Sources

Americium-241 does not occur in nature; however, some americium may be found in the environment as the result of atmospheric testing of nuclear weapons and improper disposal of wastes.

Americium-241 is associated with nuclear power sources using plutonium as a decay product. It may also be present in fallout after the detonation of a nuclear device.

Production of americium-241 is estimated at several kilograms per year, but specific production figures are not provided in the open literature.

The primary use of americium-241 is in ionization sources for smoke detectors. The average modern smoke detector for use in the home contains about 1 microCurie of Am-241 (about 0.00000029 grams) although detectors for certain industrial and commercial application contain more (as much as 50 microCuries).

History

No americium isotopes are found in nature. Americium-241 was the first isotope prepared in 1944 (by the group including Glen Seaborg, Leon Morgan, Ralph James, And Albert Ghiorso). Its preparation was accomplished by bombarding plutonium-234 with alpha particles. It was isolated (as the hydroxide) in 1945 by B.B. Cunningham. Americium was named for the Americas.

Accidental Releases of Americium-241

In August, 1976, a sixty-four year old worker at Hanford, Harold McCluskey, was heavily contaminated, and nine others contaminated to a lesser degree, with americium-241 in an accident in which a cation exchange column at an americium recovery facility exploded. The explosion was thought to be the result of a reaction between nitric acid and products produced from the radiation-induced degradation of the cation exchange resin. The treatment of Mr. McCluskey over his lifetime (he died in August, 1987 as a result of complications of coronary artery disease) became a classic study of the techniques of medical care for such exposure.

The first fine ($102,500) imposed on the U.S. Air Force in the United States by the Nuclear Regulatory Commission was the result of an incident in 1989 at Wright-Patterson Air Force base in Ohio in which an employee conducting an inventory opened one of several drums containing americium-241. The drums were being stored without proper seals, and the site was not licensed for storage of radioactive materials.

A truck carrying 900 smoke detectors overturned and burned on the A31 highway in the area of Langres in eastern France on October 9, 1999. Because individual detectors did not contain large amounts of radioactive materials, the regulations for transport did not require that the truck carry the usual warning placard, and the truck (which was also carrying combustible liquids) was allowed to burn without any actions being taken to control radioactive contamination. Notification that the truck had contained radioactive materials was not made until October 13, 1999 (by the consignee for the shipment, who was only informed on October 12 of the loss). The cumulative release was estimated at 3.96 MBq, and about 40 people were potentially contaminated, although subsequent whole-body monitoring did not detect any of the material.

Terrorists and Americium-241

Because of its ready availability from smoke detectors, Am-241 appears to have had an attraction for terrorists. In August of 2004, when the British arrested 13 people under the Terrorism Act, a number of smoke detectors were found among the materials the suspects had accumulated. While the relatively small amounts of americium used in the average smoke detector meats that the terrorists would have had to accumulate a huge number of detectors to acquire sufficient radioactive material to actually cause injury, the feeling seems to have been that simply having something that would cause radiation detectors to respond might have been enough to accomplish the terrorists' goal of seeding fear (the charges against eight of the suspects included "Conspiracy to commit a public nuisance by the use of radioactive materials, toxic gases, chemicals, and/or explosives.").

It has also been suggested that terrorists may be interested in americium because it is a fissile material that could, in theory, be used to produce a nuclear bomb. However, given that the critical mass for an explosion is of the order of 80 kilograms, while worldwide production is only a few kilograms per year, it is unlikely that enough could ever be accumulated by nonstate actors to produce an explosive fission device.

Selected References and Resources

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