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PubMed2001

Americium binding to humic acid.

The binding of americium (Am) by peat humic acid (PHA) has been investigated at Am concentrations between 10(-1) and 10(-7) M at pH approximately 2.6 in the presence and absence of Cu as a competing ion. Cu-PHA binding was also investigated in order to derive independent binding constants for use in modeling the competitive binding studies. Humic ion-binding model VI was used to compare the acquired data with previously published binding data and to investigate the importance of high-affinity binding sites in metal-PHA binding. Am was not observed to bind to high-affinity, low-concentration binding sites. The model VI parameter deltaLK2 takes into accountthe small number of strong sites in PHA and was found to be important for Cu-PHA binding but not for Am-PHA binding, regardless of whether Cu was present. Analysis of the PHA sample revealed that it contained a considerable quantity of Fe not removed by the extraction procedure, much of which is believed to be present as Fe(III). Model VI was then used to investigate the possible importance of the presence of Fe(III) in the Am-PHA binding experiments. When Fe(III) was assumed to be present, improved descriptions of the data by model VI were obtained by assuming that all of the metals [Am, Cu, and Fe(III)] undergo strong binding. This highlights the importance of Fe(III) competition in metal-PHA binding studies and possible shortcomings in the extraction procedure used to extract PHA.

Americium↗
PubMed2004

Effect of americium-241 alpha-particles on the dose-response of chromosome aberrations in human lymphocytes analysed by fluorescence in situ hybridization.

PURPOSE: To evaluate by the fluorescent in-situ hybridization (FISH) technique the dose-response and intercellular distribution of alpha-particle-induced chromosome aberrations. In particular, the validity of using the yield of characteristic types of chromosome abnormalities in stable cells as quantitative indicators for retrospective dose reconstruction has been evaluated. MATERIAL AND METHODS: Monolayers of human peripheral lymphocytes were exposed at doses from 0.02 to 1 Gy to alpha-particles emitted from a source of americium-241. The most probable energy of the alpha-particles entering the cells was 2.7 MeV. FISH painting was performed using DNA probes for chromosomes 2, 4 and 8 in combination with a pan-centromeric probe. In complete first-division cells, identified by harlequin staining, aberrations involving painted target chromosomal material were recorded as well as aberrations involving only unpainted chromosomal material. RESULTS: In total, the percentage of complex aberrations was about 35% and no dose dependence was observed. When complex-type exchanges were reduced to simple base types, the different cell distributions were clearly over-dispersed, and the linear coefficients of the dose-effect curves for translocations were significantly higher than for dicentrics. For past dose reconstruction, only a few complex aberrations were in stable cells. The linear coefficient obtained for transmissible aberrations in stable cells was more than seven times lower than that obtained in all analysed cells, i.e. including unstable cells. CONCLUSION: FISH-based analysis of complex rearrangements allows discrimination between partial-body exposures to low-linear energy transfer radiation and high-linear energy transfer exposures. In assessing past or chronic exposure to alpha-particles, the use of a dose-effect curve obtained by FISH-based translocation data, which had not excluded data determined in unstable cells, would underestimate the dose. Insertions are ineffective biomarkers because their frequency is too low.

Adult↗
PubMed1983

1976 Hanford americium exposure incident: external decontamination procedures.

An accident resulted in the deposition on an injured workman's skin surfaces, in acid-burned areas and in lacerations, of something in excess of 6 mCi 241Am. This paper describes the external decontamination procedures used, the change in americium content of the skin during the course of treatment, and some of the unusual problems encountered from the extrusion of foreign material and flaking of skin and scar tissue.

Accidents, Occupational↗
PubMed1983

1976 Hanford americium exposure incident: in vivo measurements.

Detailed external measurements were made of internally deposited 241Am in a nuclear chemical operator involved in an americium exposure accident at the Hanford plant. Despite some interference from high-level external contamination, quantitative measurements of the 241Am content in the lung, liver and bones were made starting on the third day after the accident. The rate of excretion of 241Am from these organs was determined. The 241Am embedded in the skin of the face and head was carefully mapped. The distribution over the total length of the body was also determined. Linear and rectilinear scanners, gamma cameras, large and small scintillation detectors, proportional counters, and Si(Li) and intrinsic germanium detectors were used to evaluate the internal deposition. Methods of calibration for quantitative measurement included simulation of the 241Am activity in both phantom and cadaver parts.

Absorption↗
PubMed1985

Use of DTPA for increasing the rate of elimination of plutonium-238 and americium-241 from rodents after their inhalation as the nitrates.

This study has shown that: both inhaled (2 mumol/kg) and injected (30 mumol/kg) diethylenetriaminepenta-acetic acid (DTPA) can reduce the lung deposit of 238 Pu and 241 Am inhaled as nitrate to about 1% of that in untreated controls; injection of DTPA is more effective than aerosolized DTPA for reducing deposits of 238Pu and 241Am in the liver and skeleton; combined treatment involving early inhalation of DTPA followed by repeated intravenous injections is likely to be the most effective treatment for workers who have accidentally inhaled plutonium and americium nitrates.

Aerosols↗
PubMed1986

Efficacies of LICAM(C) and DTPA for the decorporation of inhaled transportable forms of plutonium and americium from the rat.

The efficacies of N1, N5, N10, N14-tetrakis (2,3-dihydroxy-4-carboxybenzoyl)-tetra-azatetradecane [LICAM(C)] and diethylenetriaminepenta-acetic acid (DTPA) (30 mumol/kg body wt.) have been investigated for plutonium (Pu) decorporation after inhalation as the nitrate or tributyl phosphate (TBP) complexes and the data compared with those obtained after its intravenous injection as the citrate. The efficacy of removal of americium (Am) inhaled as the nitrate has also been examined. The results show that: whereas LICAM(C) and DTPA were similarly effective for removing Pu from the blood, LICAM(C) was considerably inferior to DTPA when transportable forms of Pu were inhaled; LICAM(C) is ineffective for the decorporation of Am; the optimum treatment regimen for both Pu and Am involved the prompt and repeated administration of DTPA.

Aerosols↗
PubMed1986

Multicompartment kinetic models for the metabolism of americium, plutonium and uranium in rats.

To examine the kinetic behaviour of americium, plutonium and uranium in the different organs of male and female rats an extended mammillary model has been developed; the model is composed of 10 compartments connected with 17 linear transfer coefficients. The 10 compartments describe the behaviour of the three nuclides in the blood, skeleton, liver and kidney, whereas the remaining activity is assigned to one residual organ. Each organ is divided into two compartments, a short- and long-term compartment. Morphologically, in the skeleton the short-term compartment has been assumed to be the bone surface and bone marrow and the long-term compartment to be the deep bone, whereas in the liver there is some evidence to suggest that the short-term compartment is physiologically associated with lysosomes and the long-term compartment is identical with telolysosomes. The influence of age, sex and different nuclides on the transfer coefficients and the absorbed radiation dose have been discussed. Additionally, by using the transfer coefficients calculated for intravenous injection, the behaviour of the nuclides in skeleton and liver during continuous intake has been calculated. As a second example of the application of the model the behaviour of the three nuclides in skeleton and liver after intravenous injection has been calculated with the additional assumption that from the fifth day on the animals were treated continuously with a chelating agent.

Americium↗
PubMed2005

[Emergency care for acute wound entering of plutonium and americium into the body (real case)].

The article describes a case of slowly soluble plutonium and americium compounds entering human body via skin wound. During the wound healing, the authors followed features of biokinetics of the radioactive substances, determined the major route of their excretion, evaluated efficiency of surgical d-bridement and complexation medicine (pentacin). clinical and biophysicdata collected could serve to increase efficiency of urgent therapeutic and prophylactic measures aimed to individuals with wounds contaminated with radioactive substances.

Adult↗
PubMed1985

Osteosarcoma development following single inhalation exposure to americium-241 in beagle dogs.

Young, mature Beagle dogs underwent single inhalation exposure to respirable aerosols of 241AmO2 to determine the radiation dose distribution to tissues. The dogs were serially sacrificed to assess the clearance of 241Am from the lung, the rate of translocation to internal organs, the pattern of retention in the organs, and the rates and modes of excretion. Americium dioxide was relatively soluble in the lung, leading to the translocation of significant quantities of 241Am to bone and liver, thus delivering radiation doses to these tissues nearly equal to that received by the lung. Osteoblastic osteosarcomas developed in four dogs surviving more than 1000 days after exposure. Histologically, all of the osteosarcomas were associated with areas of radiation osteodystrophy characterized by bone infarction, peritrabecular new bone formation, marrow fibrosis, and microresorptive cavities. The retention and translocation of inhaled 241Am in dogs is similar to that of man, indicating that 241Am inhaled by humans may potentially result in significant risk of bone tumor development.

Americium↗
PubMed1983

1976 Hanford americium exposure incident: overview and perspective.

Salient features of the 1976 Hanford americium exposure incident are discussed. Comparisons are made with previous human and animal exposure data, and conclusions drawn relative to the injured workman, to health physics practices, and to the adequacy of current exposure limits.

Accidents, Occupational↗
PubMedDate not supplied

[Kinetics of americium metabolism in prolonged body uptake in rats].

A study was made of the kinetics of 241Am metabolism in a rat body during long-term parenteral administration thereof. It was shown that americium 241 was deposited mainly in the skeleton and liver (47% and 51%, respectively, of the total amount accumulated in the organism) and excreted in feces.

Americium↗
PubMed1994

Biodynamic study of americium-241 accumulation in the cytosol of the hepatopancreas of the lobster Homarus gammarus.

In the lobster, most of the radionuclides ingested with contaminated food are concentrated in the digestive gland. Americium-241 accumulation in the hepatopancreas of the lobster was studied during the digestive cycle. Fractionations of cytosols at different times after ingestion of radioactive preys were performed by gel permeation chromatography to determine the distribution of 241Am in the different macromolecular components. 241Am was associated with ferritin during the whole digestive cycle. This observation suggests a correlation between 241Am distribution pathways and iron metabolism. The distribution of 241Am present in the other cytosolic proteins followed two major steps of accumulation which may be correlated to the evolution of the two main cellular types playing an important role in the digestive cycle (B and R type cells).

Americium↗
PubMedDate not supplied

Sequential isotopic determination of plutonium, thorium, americium, strontium and uranium in environmental and bioassay samples.

A procedure has been developed to provide sequential analysis of 238Pu, 230Th, 241Am, 238U, and 90Sr in environmental and bioassay samples. Tracers and/or carriers (242Pu, 243Am, 232U, and stable strontium) are added into the sample as chemical yield monitors, and then, plutonium, thorium, strontium, americium, and uranium are sequentially separated and purified by Dowex ion-exchange resin, EiChroM Sr-resin, EiChroM TRU-resin, and Chelate-100 resin, respectively. The radioactivities of 90Sr and the actinides are measured using the liquid scintillation counter and alpha-particle spectrometer, respectively. Acidified water, glass-fiber air filter, soil, synthetic urine and synthetic feces samples of US National Institute of Standard and Technology Radiochemical Intercomparison Program(NRIP) were analyzed to verify this method. All the analytical results of 238Pu, 230Th, 90Sr, 241Am and 238U meet the traceability limit per ANSI N42.22, and when appropriate, evaluation of radiobioassay measurement bias and precision per ANSI N13.30.

Chromatography, Ion Exchange↗
PubMed2001

Preparation of the thicker americium targets by molecular plating.

Electrodeposition of americium from the mixture of isopropyl alcohol and dilute nitric acid was studied. The 241,243Am targets with thickness between 600 microg/cm2 and 1.2 mg/cm2 had been prepared on thin aluminum foil (7 microm) by molecular plating at one time.

Journal Article↗
PubMed2005

Superconductivity in the americium metal as a function of pressure: probing the Mott transition.

High-pressure measurements of the resistivity of americium metal are reported to 27 GPa and down to temperatures of 0.4 K. The unusual dependence of the superconducting temperature (T(c)) on pressure is deduced. The critical field [H(c)(0) extrapolated to T=0] increases dramatically from 0.05 to approximately 1 T as the pressure is increased, suggesting that the type of superconductivity is changing as pressure increases. At pressures of approximately 16 GPa the 5f electrons of Am are changing from localized to itinerant, and the crystal structure also transforms to a complex one. The role of a Mott-type transition in the development of the peak in T(c) above 16 GPa is postulated.

Journal Article↗
PubMed2006

Many-body electronic structure of americium metal.

We report computer based simulations of energetics, spectroscopy, and electron-phonon interaction of americium using a novel spectral density functional method. This approach gives rise to a new concept of a many-body electronic structure and reveals the unexpected mixed valence regime of Am 5f6 electrons which under pressure acquire the 5f7 valence state. This explains the unique properties of Am and addresses the fundamental issue of how the localization delocalization edge is approached from the localized side in a closed shell system.

Journal Article↗