Americium isotopes

The relative activity of americium isotopes for a typical pressurized-water reactor (PWR) fuel assembly are 1,700, 11, and 13 Ci for241 Am, 242Am, and 243Am (DOE 1999). The respective activity ratios for a typical boiling water reactor (BWR) are 680, 4.6, and 4.9 Ci. There are 78 PWR and 41 BWR reactors in the United States, several of which have ceased operation. Total projected inventories of these three radionuclides for all reactors are 2.3x10s, 1.4xl06, and 1.7xl06 Ci, respectively. The post irradiation americium content of typical PWR and BWR reactor fuel assemblies are 600 g (0.09%) and 220 g (0.07%), respectively. 

Americium isotopes are transformed by radioactive decay. However, the half-lives of the principal americium isotopes, 241Am and 243Am, are very long, 432 and 7,370 years, respectively, and there is only a small amount of transformation over a human lifetime. 241Am is formed by the decay of 241Pu (half-life 14.4 years) and this can lead to a significant transformation of that isotope to 241 Am in humans, especially for 241Pu that is fixed in the bone. 

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). 

The NRC requires that the occupational intake of americium isotopes not exceed certain specified Annual Limits on Intake (ALIs) for the inhalation and oral routes of exposure. For241 Am and 243Am, the oral ingestion ALI is 0.8 JLlCi and the inhalation ALI is 0.006 pCi, both of which are based on the deterministic dose limit to the bone surface (NRC 2000). 

There are methods available to quantify the total mass of americium in environmental samples. Mass spectrometric methods provide total mass measurements of americium isotopes (Dacheux and Aupiais 1997, 1998 Halverson 1984 Harvey et al. 1993) however, these detection methods have not gained the same popularity as is found for the radiochemical detection methods. This may relate to the higher purchase price of a MS system, the increased knowledge required to operate the equipment, and the selection by EPA of a-spectrometry for use in its standard analytical methods. Fluorimetric methods, which are commonly used to determine the total mass of uranium and curium in environmental samples, have limited utility to quantify americium, due to the low quantum yield of fluorescence for americium (Thouvenout et al. 1993). 

Actinides were determined at the ultratrace level in moss samples collected from the eastern Italian Alps (1500 m a.s.l.). The frozen samples were cut into 1-2 cm sections and analyzed separately to obtain the distribution curves of the vertical concentrations. For plutonium and americium isotope analysis, 1-2 g of the samples were ashed, leached, separated with respect to analytes and analyzed by alpha spectrometry and LA-ICP-MS after the plutonium or americium had been electroplated on a stainless steel disk.23 Estimated limits of quantification of LA-ICP-MS for actinide radionuclides deposited on stainless steel plates after chemical separation are summarized in Table 9.45. For most of the long-lived radionuclides in moss samples, lower limits of determination were found at the 10 15gg 1 concentration level compared to those of a - spectrometry 23... 

Table 4.2 indicates that over 95% of the radiation in spent fuels presented for separation arises principally from 137Cs and 90Sr, the remaining part being mainly due to americium isotopes that are a emitters. Similarly, the bulk of some 1.5-W/kg heat load from radioactivity is due to these nuclides. Presently, two ways are followed, either the disposal of spent fuel (current policy in the United States) or the spent... 

Section Data for the Higher Plutonium Isotopes in the Resonance Region, Proc. Specialists Mtg. on Nucl. Data of Higher Plutonium and Americium Isotopes for Reactor Applications, Brookhaven National Laboratory, Nov. 20-22,... 

The isotope 242Cm was first isolated among the products of a-bombardment of 239Pu, and its discovery actually preceded that of americium. Isotopes of other elements were first identified in products from the first hydrogen bomb explosion (1952) or in cyclotron bombardments. Although Cm, Bk, and Cf have been obtained in macro amounts (Table 20-2), much of the chemical information has been obtained on the tracer scale. For the later elements, i.e., those with Z > 100, identification of a few atoms of short lifetime has required the use of very rapid separation techniques and detection based on their nuclear properties. 

The americium isotope Am is used in smoke detectors. Describe the composition of a neutral atom of this isotope for protons, neutrons, and electrons. 

The longest-lived americium isotope is Am (tj/2 = 7380 years). While americium isotopes with mass numbers from 234 to 247 are known, Am and Am are the most important and the most useful for chemical research. Extensive reviews can be found in refs 3-16 and 367. 

The slow dissolution behaviour of the plutonium and americium isotopes was similar to that reported for insoluble plutonium oxides. The moderate uranium dissolution behaviour was similar to that reported on filters from personal air samplers of uranium miners. ... 

AMERICIUM. A man-made element, with atomic number 95 and symbol Am. All known americium isotopes are radioactive mate-riai. Americium-243 is an aipha particie emitter and has been used... 

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