Americium compounds

Retention and Absorption Estimates in Animals Exposed to Americium Compounds by Inhalatidii 3-2. Absorption Estimates in Animals Exposed to Americium Compounds by Ingestion 3-3. Tissue Americium Levels from Human Autopsies... 

Physical and Chemical Properties of Americium and Selected Americium Compounds... 

Available information from human exposures indicates that airborne americium-containing particles are deposited in the respiratory tract, cleared to some extent via mucociliary action, and swallowed or expelled (Edvardsson and Lindgren 1976 Fry 1976 Newton et al. 1983 Sanders 1974 Toohey and Essling 1980). Descriptions of human respiratory tract models that can be used for radiation protection also include relevant information regarding biokinetics of inhaled particles (ICRP 1994b, 1995 NCRP 1997). Quantitative data are not available, however. Supporting animal studies include inhalation exposure to aerosols of americium (Buldakov et al. 1972 DOE 1978 Gillett et al. 1985 Sanders and Mahaffey 1983 Talbot et al. 1989 Thomas et al. 1972) or intratracheal instillation of americium compounds (Moushatova et al. 1996). 

Table 3-1. Retention and Absorption Estimates in Animals Exposed to Americium Compounds by Inhalation...

The ICRP (1994b, 1995) developed a Human Respiratory Tract Model for Radiological Protection, which contains respiratory tract deposition and clearance compartmental models for inhalation exposure that may be applied to particulate aerosols of americium compounds. The ICRP (1986, 1989) has a biokinetic model for human oral exposure that applies to americium. The National Council on Radiation Protection and Measurement (NCRP) has also developed a respiratory tract model for inhaled radionuclides (NCRP 1997). At this time, the NCRP recommends the use of the ICRP model for calculating exposures for radiation workers and the general public. Readers interested in this topic are referred to NCRP Report No. 125 Deposition, Retention and Dosimetry of Inhaled Radioactive Substances (NCRP 1997). In the appendix to the report, NCRP provides the animal testing clearance data and equations fitting the data that supported the development of the human mode for americium. 

Americium metal has been obtained by heating americium oxide, Am203, with lanthanum at 1,200 °C americium, which is more volatile than other actinides, volatilizes and can readily be separated from other actinides. Am02 can be obtained by igniting most trivalent americium compounds (Budavari 1996 Cotton and Wilkinson 1980 UIC 1997). 

There is limited information available regarding the abiotic transformation of americium in the atmosphere. Oxidation is the most common reaction that occurs in the atmosphere. This would not be expected for americium compounds, which are generally present in the +3 oxidation date under environmental conditions. 

Physical, Chemical, and Radiological Properties. Data on the physical and chemical properties of americium and americium compounds are available in the literature (Cotton and Wilkinson 1980 Lide 1994, 1998 Nenot and Stather 1980 Seaborg 1991). Data are also available on the radiological properties of americium isotopes (ICRP 1983 Lide 1998). 

No inhalation or oral MRLs were derived for americium or americium compounds. 

The Chemistry of Americium Compounds. Report AECD-1930 (Marz 1948). 

The Preparation of Anhydrous Americium Compounds. J. Amer. chem. 

Table 1 Heats of formation of americium compounds and ions...

All pentavalent americium compounds are complex salts. Examples are KAm02C03, KAm02F2 and Li3Am04. These are formed upon oxidation of Am3+. For example, Am3+ reacts with hypochlorite ion in hot K2CO3, precipitating KAm02C03 as a crystaUine sohd. 

Americium is a critical ingredient in smoke detectors. Some of the tiny particles released by an americium compound create a small electric charge inside smoke detectors. Smoke or soot can block the charge, which sets off the alarm. One gram of americium is enough for 5,000 smoke detectors. 

The reaction conditions and the lattice constants of the americium compounds described in the following sections are listed in Tables I and II. 

Most of the compounds of tetravalent to hexavalent americium described here were obtained for uranium, neptunium, and plutonium (Table III). The decomposition temperatures of the americium compounds are considerably below (200°-300°C.) those of the corresponding temperatures of the analogous neptunates and plutonates (4, 25). 

Mossbauer studies of americium compounds have shown that changes in the chemical isomer shift, d, with the oxidation state of the americium may be attributed to increases in the electron density at the nucleus resulting from removal of 5/ electrons. ... 

Fig. 1. Susceptibilities versus temperature of americium compounds. The values for Am metal, AmN and AmAs are taken from Kanellakopu-los et al, (1975). The values for AmBi and AmTe are our own measurements.

Much work has been done on the charge states of neptunium following alpha decay in various americium compounds and frozen solutions. 

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