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At least 1,279 records · Page 71Linked to original sources
PubMed1993

Single-breath inhalation or rebreathing of gases labelled with positron emitters: some technical aspects of dispensing and waste gas management.

A simple and reliable system for the single-breath inhalation and for short-term rebreathing of radioactive gases used in positron emission tomography is described. It comprises a collection- and radioactivity measurement-device, an inhalation bag for single-breath application, a modified anaesthetic system for rebreathing and a patient exhaled gas management system. The system is mainly used with 15O-labelled gases, but allows also the use of longer lived tracers such as methyl fluoride labelled with 18F or 11C.

Administration, Inhalation↗
PubMed2000

Reconstruction of radionuclide contamination of the Techa River caused by liquid waste discharge from radiochemical production at the Mayak Production Association.

Because of its importance to reconstructing radiation doses for ongoing epidemiological studies, a feasibility study was undertaken to determine if the source term of radioactive materials released to the Techa River from the Mayak Production Association, the first facility in the former Soviet Union for the production of plutonium, could be reconstructed from historical measurements made at a limited number of downriver locations. The feasibility study used historically measured water flow rates and total-beta radioactivity measurements, and considered the processes of radioactive decay and of sorption/desorption. A simple radionuclide mass balance approach was used. To determine the rate of input of radionuclides to the Techa River system, the Techa River was depicted as a series of segments for which measurements are available. For each segment of the river, a system of recurrent (with time) equations was compiled for radioactivity balance accounting for the radioactivity inflow at the inflowing end, activity discharge with water at the outflowing end, and the reduction of activity because of radioactive decay. The equations change with time to account for the changing nature of the river regime. Effective sorption constants for 90Sr and 137Cs, which characterize the transport of radionuclides among the river system components (water and bottom sediments), were defined based on the inventory of these radionuclides deposited at each of the studied river segments and data on water concentration and radioactive removal. All the information on radioactive contamination of the river system components during the period 1949-1996 was used. Solution of the series of equations provided information on the rate of input of these radionuclides into the upper end of the river. The pilot study indicated that it is possible to determine the historical releases of a wider suite of radionuclides using the historical monitoring data from numerous locations along the river, rather than relying on a more uncertain reconstruction of quantities released at the point of discharge. Radionuclides considered include 90Sr, 106Ru, 137Cs, and 144Ce. Estimated concentrations of selected radionuclides at various times are presented.

Feasibility Studies↗
PubMed2004

Using multimedia modeling to expedite site characterization.

GOAL, SCOPE AND BACKGROUND: This paper uses two case studies of U.S. Department of Energy nuclear weapons complex installations to illustrate the integration of expedited site characterization (ESC) and multimedia modeling in the remedial action decision making process. CONCEPTUAL SITE MODELS, MULTIMEDIA MODELS, AND EXPEDITED SITE CHARACTERIZATION: Conceptual site models outline assumptions about contaminates and the spatial/temporal distribution of potential receptors. Multimedia models simulate contaminant transport and fate through multiple environmental media, estimate potential human exposure via specific exposure pathways, and estimate the risk of cancer and non-cancer health outcomes. ESC relies on using monitoring data to quantify the key components of an initial conceptual site model that is modified iteratively using the multimedia model. CASE STUDIES: Two case studies are presented that used the ESC approach: Los Alamos National Laboratory (LANL) and Pantex. LANL released radionuclides, metals, and organic compounds, into canyons surrounding the facility. The Pantex Plant has past waste management operations which included burning chemical wastes in unlined pits, burying wastes in unlined landfills, and discharging plant wastewaters into on-site surface waters. CONCLUSIONS: The case studies indicate that using multimedia models with the ESC approach can inform assessors about what, where, and how much site characterization data needs to be collected to reduce the uncertainty associated with risk assessment. Lowering the degree of uncertainty reduces the time and cost associated with assessing potential risk and increases the confidence that decision makers have in the assessments performed.

Decision Making↗
PubMed2003

Granulated activated carbon modified with hydrophobic silica aerogel-potential composite materials for the removal of uranium from aqueous solutions.

Aqueous solutions of 100 parts per billion (ppb) uranium at pH 7 were treated with granulated activated carbon (GAC) that had been modified with various formulations of hydrophobic aerogels. The composite materials were found to be superior in removing uranium from a stock solution compared to GAC alone evaluated by a modified ASTM D 3860-98 method for batch testing. The testing results were evaluated using a Freundlich adsorption model. The best performing material has parameters of n = 287 and Kf = 1169 compared to n = 1.00, and Kf = 20 for GAC alone. The composite materials were formed by mixing (CH3O)4Si with the hydrophobic sol-gel precursor, (CH3O)3SiCH2CH2CF3 and with specified modifiers, such as H3PO4, Ca(NO3)2, and (C2H5O)3SiCH2CH2P(O)(OC2H5)2, elation catalysts, and GAC in a supercritical reactor system. After gelation, supercritical extraction, and sieving, the composites were tested. Characterization by FTIR and 31P NMR indicate the formation of phosphate in the case of the H3PO4 and Ca(NO3)2 composites and phosphonic acid related compounds in the phosphonate composite. These composite materials have potential application in the clean up of groundwater at DOE and other facilities.

California↗
PubMed1984

The assessment of human exposure to radionuclides from a uranium mill tailings release and mine dewatering effluent.

This study provides an assessment of human exposure to radiation from a river system contaminated by radionuclides of the 238U decay series released through a dam break at a uranium mill tailings pond and by the continuous discharge of dewatering effluent from 2 uranium mines. The in vivo analyses of radionuclides in 6 Navajo Indians who lived near the river indicate no detectable elevations above background concentrations. Dose estimates for inhalation of suspended river sediment indicate a maximum annual 50-yr dose commitment of 204 mrem to the endosteum. Estimates of doses (50-yr dose commitments) from the ingestion of livestock range between 1 mrem (to liver) and 79 mrem (to bone) suggest that the major contribution to human exposure is from mine dewatering effluent that has been continuously released into the river system for many years. Although the estimated exposures do not exceed existing state or federal regulations, their magnitude justifies further measurement of radionuclides in animals and in the natural environment and the consideration of strategies to reduce radiation exposure to humans and animals.

Accidents, Occupational↗
PubMed1985

A field experiment on Rn flux from reclaimed uranium mill tailings.

Design and construction techniques are described for a 1.6 ha experimental reclamation plot consisting of a 1-m-thick slab of uranium mill tailings covered with various depths of overburden. A passive, activated charcoal device was developed and used for measurements of Rn flux at the soil surface. Observations on Rn flux vs overburden depth indicated that tailings covered with 1.5 m of revegetated or 0.3 m of bare overburden had Rn exhalation rates comparable to background. Vegetated subplots exhibited a significantly higher (often an order of magnitude) flux than the bare subplots. A positive correlation was observed between precipitation quantities and Rn flux.

Metallurgy↗
PubMed1985

The origin of I in soil and the 129I problem.

It is widely believed that the I in soil is derived from the I in oceans by evaporating-atmospheric transport-washout by rain over land, rather than from the I in rock when the latter is weathered into soil. Since human I burdens are derived largely from soil by plant root uptake into food, this implies that the specific activity of 129I in the I of human thyroids will be the same as that in the oceans, whereas it would be similar to that in rock (much lower) if the I in soil were derived from weathering of rock as is the case for other heavy trace elements. The bases for the oceanic origin theory are analysed and found not to be in accord with modern data. Recent data shows no correlation between concentration of I in soil and proximity to oceans, which argues strongly against the oceanic origin theory. Some problems with long-distance atmospheric transport are pointed out. It is shown that the balance between I input to soil during soil formation by rock weathering and output from soil by erosion leaves little room for contributions from oceanic sources. It is concluded that only a small fraction of the I in soil is of oceanic origin. Most estimates of very long-term effects of 129I on human health are therefore several times too high.

Food Contamination, Radioactive↗
PubMedDate not supplied

Stochastic study of solute transport in a nonstationary medium.

A Lagrangian stochastic approach is applied to develop a method of moment for solute transport in a physically and chemically nonstationary medium. Stochastic governing equations for mean solute flux and solute covariance are analytically obtained in the first-order accuracy of log conductivity and/or chemical sorption variances and solved numerically using the finite-difference method. The developed method, the numerical method of moments (NMM), is used to predict radionuclide solute transport processes in the saturated zone below the Yucca Mountain project area. The mean, variance, and upper bound of the radionuclide mass flux through a control plane 5 km downstream of the footprint of the repository are calculated. According to their chemical sorption capacities, the various radionuclear chemicals are grouped as nonreactive, weakly sorbing, and strongly sorbing chemicals. The NMM method is used to study their transport processes and influence factors. To verify the method of moments, a Monte Carlo simulation is conducted for nonreactive chemical transport. Results indicate the results from the two methods are consistent, but the NMM method is computationally more efficient than the Monte Carlo method. This study adds to the ongoing debate in the literature on the effect of heterogeneity on solute transport prediction, especially on prediction uncertainty, by showing that the standard derivation of solute flux is larger than the mean solute flux even when the hydraulic conductivity within each geological layer is mild. This study provides a method that may become an efficient calculation tool for many environmental projects.

Adsorption↗