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Applications of pulse radiolysis to imaging sciences

Description: Pulse radiolysis has been used over the last 3 decades to study a variety of physical and chemical systems, including those relevant to imaging processes. This review outlines the similarities between photolysis and radiolysis and highlight the differences. It focuses on time-resolved variants of the two disciplines, flash photolysis vs pulse radiolysis. The strength (and weakness) of the radiolytic techniques is their nonspecificity; the energy is always absorbed by the solvent and not the solute. Radiation chemistry principles that were developed for one discipline are easily transportable to another. The pulse radiolysis technique with a wide arsenal of detection techniques is currently used to identify short-lived intermediates and to determine their kinetic and thermodynamic properties. Together, these studies provide mechanistic insight into the behavior of physical systems. We demonstrate the utility of the approach in several areas of interest to imaging sciences: clustering of silver atoms, growth of silver halides, and medium effects on these systems.
Date: May 1, 1996
Creator: Meisel, D.
Partner: UNT Libraries Government Documents Department

Radiation induced growth of micro crystallites

Description: Generation of colloidal particles during the radiolysis of aqueous solutions was already observed in the early days of radiation chemistry. Systematic studies using radiation chemistry techniques as synthetic tools in the preparation of colloidal particles, primarily metallic particles, were begun approximately a decade ago in conjunction since they were found to catalyze multi-electron redox processes. A large number of metallic colloidal particles were then synthesized, including silver, gold, platinum, iridium, nickel, cadmium, and others. More recently, attention has turned to semiconductor colloidal particles. The stimulus to these studies is the observation of quantum size effects in small semiconductor particles that exhibit hybrid properties between those of the molecular species and the solid state bulk material. In the following we discuss our own observations on the evolution of semiconductor particles whose growth has been initiated by pulse radiolysis. 13 refs., 2 figs.
Date: January 1, 1991
Creator: Meisel, D.
Partner: UNT Libraries Government Documents Department

The NO{sub x} system in nuclear waste. Annual report

Description: The authors highlight their results from the title project. The project is a coordinated effort of the three Co-PIs to assist the Safety Programs at the Hanford and other DOE Environmental Management Sites. They present in the report their observations and interactively discuss their implications for safety concerns. They focus on three issues: (1) reducing radicals in the NO{sub x} system; (2) aging of organic chelators and their degradation products by NO{sub 2}; and (3) interfacial processes in aqueous suspensions. The goal of this project is to establish the chemistry and physics that dominate the radiolytically initiated processes that occur in waste tanks across the DOE complex.
Date: September 30, 1997
Creator: Meisel, D.; Camaioni, D. & Orlando, T.
Partner: UNT Libraries Government Documents Department

Chemistry, radiation, and interfaces in suspensions of nuclear waste simulants

Description: We focus in this report on three issues that are of central importance in the management of radioactive high-level liquid waste (HLLW). We show that the only reducing radical that lasts longer than a few ps in typical HLLW, and is capable of generating hydrogen, is NO{sub 3}{sup 2-}. We measured the lifetime of this species across the whole pH range (3 {le} pH {le} 14) and found it to be shorter than {approx}15 {mu}s, before is dissociates to give strongly oxidizing NO{sub 2} radicals. We found that it reacts with many proton donors (H{sup +} phosphate, borate, NH{sub 4}{sup +}, amines) in a reaction that is not merely an acid-base equilibrium reaction. Using high-level ab initio calculations we estimate its redox potential and pK{sub a}. We have developed methodologies to study the degradation of organic additives to the HLLW (to CO{sub 2} or carbonate) by NO{sub 2}. Relative rates of degradation of several complexants were determined using competition kinetics and {sup 13}C NMR and proton NMR detection techniques. Direct absorption of the radiation (low-energy electrons as well as photons above the ionization threshold) in NaNO{sub 3} single crystal at the solid/vacuum interface led to production of NO, O, and O- as the major products.
Date: August 1997
Creator: Meisel, D.; Cook, A.; Camaioni, D. & Orlando, T.
Partner: UNT Libraries Government Documents Department

The NOx system in nuclear waste. 1997 annual progress report

Description: 'The authors highlight their results from the title project. The project is a coordinated effort of the three Co-PIs to assist the Safety Programs at the Hanford and other DOE Environmental Management Sites. The authors present in the report their observations and interactively discuss their implications for safety concerns. They focus on three issues: (1) Reducing radicals in the NOx system The authors show that the only reducing radical that lasts longer than a few ns in typical waste solutions, and is capable of generating hydrogen, is NO{sub 3}{sup 2-}. The authors measured the lifetime of this species across the whole pH range (3 {le} pH {le} 14) and found it to be shorter than -15 \265s, before it dissociates to give the strongly oxidizing NO, radicals. They found that it reacts with many proton donors (H{sup +}, phosphate, borate, NH{prime}, amines) in a reaction that is not merely an acid-base equilibrium reaction but is probably a dissociative proton transfer. They estimate the redox potential from theoretical considerations and obtain an experimental verification. They conclude that it is highly unlikely, although thermodynamically possible, that this radi-cal will generate hydrogen in waste solutions. (2) Aging of organic chelators and their degradation products by NO, Methodologies to study the degradation of organic substrates (including the important waste components, formate and oxalate) to CO;, or carbonate, by NO, were developed. This radical dimerizes and disproportionates to nitrate and nitrite. Therefore, mineraliza-tion of the organic substrates competes with the disproportionation of NO,. Among the organic substrates, formate and oxalate are also mineralized but because they are of low fuel value their mineralization is not very helpful, yet it consumes NO,. (3) Interfacial processes in aqueous suspensions Yields of charge transfer from solid silica particles to water and other liquids were meas-ured. If the particles ...
Date: January 1, 1997
Creator: Meisel, D.; Camaioni, D. & Orlando, T.
Partner: UNT Libraries Government Documents Department

Interfacial radiolysis effects in tank waste speciation. 1998 annual progress report

Description: 'The purpose of this program is to deliver pertinent, fundamental information that can be used to make technically defensible decisions on safety issues and processing strategies associated with storage and clean up of DOE mixed chemical and radioactive wastes. The radioactive and chemical wastes present in DOE underground storage tanks contain complex mixtures of sludges, salts, and supernatant liquids. These mixtures, which contain a wide variety of oxide materials, aqueous solvents, and organic components, are constantly bombarded with gamma quanta, beta and alpha particles produced via the decay of radioactive isotopes. Currently, there is a vital need to understand radiolysis of organic and inorganic species present in mixed waste tanks because these processes: (a) produce mixtures of toxic, flammable, and potentially explosive gases (i.e., H{sub 2}, N{sub 2}O and volatile organics) (b) degrade organics, possibly to gas-generating organic fragments, even as the degradation reduces the hazards associated with nitrate-organic mixtures, (c) alter the surface chemistry of insoluble colloids in tank sludge, influencing sedimentation and the gas/solid interactions that may lead to gas entrapment phenomena. This report summarizes the technical achievements of a 3-year project that is now in its 2nd year. Progress in three areas is reported: (1) radiation effects at NaNO 3 crystal interfaces, (2) reactions of organic complexants with NO{sub 2} in water, and (3) radiation effects in oxide particles.'
Date: June 1, 1998
Creator: Orlando, T. M.; Camaioni, D. & Meisel, D.
Partner: UNT Libraries Government Documents Department

The NOx system in nuclear waste. 1998 annual progress report

Description: 'The objective of this project is to assist EM sites in the resolution of outstanding safety issues involved in the temporary storage of high-level waste (HLW) in large tanks. To achieve this objective, mechanisms of the radiolytic and radiolytically induced processes that occur in the waste are quantitatively studied. The information is incorporated into a computer modeling of the tanks chemistry under various scenarios and the predicted results are rapidly conveyed to the site operators. This report summarizes the technical achievements of a 3-year project that is now in its 2nd year of operation. The project is a collaborative effort between the ANL and PNNL and is strongly coupled to another EMSP project (``Interfacial Radiolysis Effects in Tank Waste Speciation'''' PI: T. Orlando, PNNL) and to the safety programs at the Hanford site (``Organic Tanks Safety Program: Waste Aging Studies'''', PI D. Camaioni, PNNL). Information from the project is also shared directly with Westinghouse Savannah River personnel. In general, the basic studies are performed at ANL and PNNL and the information is continuously shared with Tanks Safety Programs. To further facilitate the exchange of information and the immediate incorporation of results into operations, the authors conducted at least twice a year coordination meetings at the various laboratories where the site operators (e.g. from DE and SH, Numatec, WSRC, etc.) participate, both to present their needs and to obtain updated information.'
Date: June 1, 1998
Creator: Meisel, D. & Camaioni, D.
Partner: UNT Libraries Government Documents Department

Charge injection into small semiconductor particles

Description: We report on the effect of the injection of electrons into small CdS particles on their spectroscopy. Solvated electrons were generated pulse radiolytically and their reaction with the particles was monitored. As a result of the excess charge, the absorption by the particle in the exciton region is bleached. The bleaching tacks the shift in band edge as the particle size decreases. However, excess electrons in larger particles are more efficient tan in small particles. It is concluded that the effort originates in the electric field effect generated by the excess charge.
Date: June 1, 1995
Creator: Lawless, D.; Luangdilok, C.; Cook, A.R. & Meisel, D.
Partner: UNT Libraries Government Documents Department

Excess charges in semiconductor nanocrystallites

Description: The authors explore in this report the effects of excess electrons on the edge of the absorption spectrum of small semiconductor particles. The presence of these charges leads to strong bleaching of the absorption at the exciton region and to slight enhancement of the absorption on both sides of the bleaching. They show that the effect is independent of the origin of the charge; it occurs whether the charge is injected into the particle or only attached to its surface, and it appears even when the charge is deeply localized within the band gap. They conclude that the effect arises from the electric field associated with the charge and not from its presence in the band.
Date: June 1, 1995
Creator: Laungdilok, C.; Lawless, D.; Cook, A.R. & Meisel, D.
Partner: UNT Libraries Government Documents Department

Interfacial Radiolysis Effects in Tank Waste Speciation

Description: The intent of this program was to establish an understanding of the role of solid-state radiolysis, secondary electron interactions, charge transfer dynamics and the general effect of heterogeneous solids (interfaces and particulate surface chemistry) on tank waste radiation processes. Specifically, there was a need to understand the role of interfaces and solids in the generation of noxious gases and the mechanisms of organic compound degradation.
Date: June 1, 2000
Creator: Orlando, Thomas M.; Meisel, D. & Camaioni, D.M.
Partner: UNT Libraries Government Documents Department

Gas generation from Hanford grout samples

Description: In an extension of our work on the radiolytic processes that occur in the waste tanks at the Hanford site, we studied the gas generation from grout samples that contained nuclear waste simulants. Grout is one option for the long-term storage of low-level nuclear waste solutions but the radiolytic effects on grout have not been thoroughly defined. In particular, the generation of potentially flammable and hazardous gases required quantification. A research team at Argonne examined this issue and found that the total amount of gases generated radiolytically from the WHC samples was an order of magnitude higher than predicted. This implies that novel pathways fro charge migration from the solid grout to the associated water are responsible for gas evolution. The grout samples produced hydrogen, nitrous oxide, and carbon monoxide as well as nitrogen and oxygen. Yields of each of these substances were determined for doses that are equivalent to about 80 years storage of the grout. Carbon monoxide, which was produced in 2% yield, is of particular importance because even small amounts may adversely affect catalytic conversion instrumentation that has been planned for installation in the storage vaults.
Date: March 1, 1996
Creator: Jonah, C.D.; Kapoor, S.; Matheson, M.S.; Mulac, W.A. & Meisel, D.
Partner: UNT Libraries Government Documents Department

The origin of hydrogen generated from formaldehyde in basic solutions

Description: The isotopic composition of dihydrogen generated from formaldehyde in highly basic solutions has been investigated. It is shown that two pathways contribute to the generation of dihydrogen. In the first pathway, one hydrogen atom originates from water and the other from formaldehyde. In the second pathway both hydrogen atoms originate from the methylene moiety of the formaldehyde. For production of dihydrogen from glyoxylate only the first pathway is observed.
Date: March 1, 1996
Creator: Kapoor, S.; Barnabas, F.; Jonah, C.D.; Sauer, M.C. Jr. & Meisel, D.
Partner: UNT Libraries Government Documents Department

Radiation chemistry of synthetic waste

Description: The yield of H{sub 2} from radiolysis of aqueous solutions is substantially reduced by the presence of nitrate and nitrite in the waste solutions. Nitrate is more efficient in scavenging the precursors to H{sub 2} than is nitrite, therefore, the latter should be maintained at higher levels if minimization of radiolytic gas production is required. Nitrate is the major scavenger for e{sub aq}{sup {minus}} and nitrite is the major scavenger for H atoms. At the concentration levels of the waste solutions some fraction of the radiation energy will be absorbed directly by the solutes, primarily the nitrate/nitrite components. Organic additive will increase the generation of H{sub 2} and mechanistic information is available to allow predictive modeling of trends in the rate of the generation. Physical parameters such as temperature, viscosity, and pressure will not significantly affect the gas generation relative to its generation under normal conditions. Radiolytic generation of N{sub 2}O is very inefficient in the absence of organic solutes. No mechanistic information is available on its generation in the presence of organic additives. At the concentration levels of the inorganic salts in the waste solutions, it will be very difficult to find a chemical additive that could efficiently reduce the yield of the generated H{sub 2}, except, perhaps, increasing the concentration of the nitrite/nitrate components.
Date: November 1, 1991
Creator: Meisel, D.; Diamond, H.; Horwitz, E.P.; Jonah, C.D.; Matheson, M.S.; Sauer, M.C. Jr. et al.
Partner: UNT Libraries Government Documents Department

Radiolytic and radiolytically induced generation of gases in simulated waste solutions

Description: The radiolytic generation of gases in simulated mixed waste solutions was studied. Computer modeling of the non-homogeneous kinetic processes in these highly concentrated homogeneous solutions was attempted. The predictions of the modeling simulations were verified experimentally. Two sources for the radiolytic generation of H{sub 2} are identified: direct dissociation of highly energetic water molecules and hydrogen abstraction from the organic molecules by hydrogen atoms. Computer simulation of the homogeneous kinetics of the NO{sub X} system indicate that no N{sub 2}O will be produced in the absence of organic solutes and none was experimentally detected. It was also found that long term pre-irradiation of the simulated waste solutions leads to enhanced thermal production of these two gases. 22 refs., 5 figs., 3 tabs.
Date: January 1, 1990
Creator: Meisel, D.; Sauer, M.C. Jr.; Jonah, C.D.; Diamond, H.; Matheson, M.S.; Barnabas, F. et al.
Partner: UNT Libraries Government Documents Department

Nitrous oxide production from radiolysis of simulted high-level nuclear waste solutions

Description: Nitrous oxide gas (N{sub 2}O) is produced by the radiolysis of aqueous nitrate or nitrite solutions in the presence of organic compounds. When ethylenediaminetetraacetic acid (EDTA) or N- (2-hydroxyethyl)-ethylenediaminetriacetic acid (HEDTA) is present, the G-value for hydrogen increases and N{sub 2}O become the major gaseous product (G=0.54). A survey of organic compounds indicates the amount of N{sub 2}O formed depends on the structure of the organic. With highly oxidized organics (carbonate, formate, acetate and oxalate), little or no N{sub 2}O is formed. Aromatic and aliphatic organics (sodium tetraphenylborate, benzene, phenol, n-paraffin, and tributylphosphate) produce small amounts of N{sub 2}O. Water soluble, easily oxidized organics (methanol, ethanol, isopropanol, n-butanol, acetone, and ethylene glycol) produce large amounts of N{sub 2}O relative to the previous two categories. Nitrous oxide production is not greatly affected by pH between neutral and pH=13, but increases significantly in acid solution. The G-value for N{sub 2}O production in 10 wt% potassium tetraphenylborate slurries has been measured under process conditions important at the Savannah River Site.
Date: January 1, 1992
Creator: Walker, D.D.; Hobbs, D.T.; Tiffany, J.B.; Bibler, N.E. (Westinghouse Savannah River Co., Aiken, SC (United States)) & Meisel, D. (Argonne National Lab., IL (United States))
Partner: UNT Libraries Government Documents Department

Radiolytic generation of gases from synthetic waste

Description: Yields of H{sub 2}, N{sub 2}O, O{sub 2}, and N{sub 2}, in simulated waste solutions, containing high nitrate, nitrite, hydroxide and aluminate, were experimentally measured in the presence and absence of moderate concentrations of organic chelators and some of their degradation products. These yields were measured at 30 and 60{degrees}C. No effect of dose rate on yield of H{sub 2} was observed and the amount of H{sub 2} increases linearly with dose and with the concentration of the organic additive. The generation of N{sub 2}O was observed only when organic solutes were present and its yield was dose rate dependent. Rate constants for H atom abstraction from the organic component by free H atoms were determined and these were correlated with the efficiency of the organic solute and in the generation of H{sub 2}. The rate of thermal generation of H{sub 2} and N{sub 2}O was also measured and was found to substantially increase in solutions that were preirradiated, presumably due to the generation of radiolytic degradation products. Computer modeling of the radiolytic precesses show the yield of H{sub 2} is strongly dependent on the nitrite concentration; the yield decreases with increasing nitrite concentration. The yield will be only weakly dependent on nitrate concentration above 0.5 M. Simulation of the homogeneous reactions that describe the chemistry of the NO{sub x} system indicate that: no N{sub 2}O will be formed in the absence of NO{sub x}-organic reactions. 18 refs., 41 figs., 13 tabs.
Date: December 1, 1991
Creator: Meisel, D.; Diamond, H.; Horwitz, E.P.; Jonah, C.D.; Matheson, M.S.; Sauer, M.C. Jr. et al.
Partner: UNT Libraries Government Documents Department

Evaluation of the generation and release of flammable gases in tank 241-SY-101

Description: Tank 241-SY-101 is a double shell, high-level waste tank located in the 200 West Area of the Hanford Site. This tank contains about 1 million gallons of waste that was concentrated at the 242-S Evaporator. Shortly after the waste was put in the tank, the waste began to expand because the generation of gases. In 1990 this tank was declared to have an unreviewed safety question because of the periodic release of hydrogen and nitrous oxide. A safety program was established to conduct a characterization of the waste and vented gases and to determine an effective means to prevent the accumulation of flammable gases in the tank dome space and ventilation system. Results of the expanded characterization conducted in fiscal year 1991 are presented. The use of gas chromatographs, mass spectrometers, and hydrogen-specific monitors provided a greater understanding of the vented gases. Additional instrumentation placed in the tank also helped to provide more detailed information on tank temperatures, gas pressure, and gas flow rates. An extensive laboratory study involving the Westinghouse Hanford Company, Pacific Northwest Laboratory, Argonne National Laboratory, and the Georgia Institute of Technology was initiated for the purpose of determining the mechanisms responsible for the generation of various gases. These studies evaluate both radiolytic and thermochemical processes. Results of the first series of experiments are described.
Date: November 1, 1991
Creator: Babad, H.; Johnson, G.D.; Lechelt, J.A.; Reynolds, D.A. (Westinghouse Hanford Co., Richland, WA (United States)); Pederson, L.R.; Strachan, D.M. (Pacific Northwest Lab., Richland, WA (United States)) et al.
Partner: UNT Libraries Government Documents Department

Gas generation and retention in Tank 101-SY: A summary of laboratory studies, tank data, and information needs

Description: Chemical and radioactive wastes from processes used to separate plutonium from uranium are stored in underground tanks at the Hanford Site in Washington state. In March 1981, it was observed that the volume of wastes in Tank 101-SY slowly increased, followed by a rapid decrease and the venting of large quantities of gases. These cycles occurred every 8 to 15 weeks and continue to the present time. Subsequent analyses showed that these gases were composed primarily of hydrogen and nitrous oxide (N{sub 2}O). In response to the potential for explosion and release of hazardous materials to the environment, laboratory programs were initiated at Argonne National Laboratory (ANL), Georgia Institute of Technology (GIT), Pacific Northwest Laboratory (PNL), and Westinghouse Hanford Company (WHC), to develop a better understanding of the physical and chemical processes occurring in this waste tank. An aggressive sampling and analysis effort is also under way to characterize the wastes as fully as possible. These efforts will provide a technically defensible basis for safety analyses and future mitigation/remediation of the tank and its contents.
Date: June 1, 1992
Creator: Pederson, L.R. (comp.) (Pacific Northwest Lab., Richland, WA (United States)); Ashby, E.C. (Georgia Inst. of Tech., Atlanta, GA (United States)); Jonah, C.; Meisel, D. (Argonne National Lab., IL (United States)) & Strachan, D.M. (Pacific Northwest Lab., Richland, WA (United States))
Partner: UNT Libraries Government Documents Department

Basic Research Needs for Countering Terrorism

Description: To identify connections between technology needs for countering terrorism and underlying science issues and to recommend investment strategies to increase the impact of basic research on efforts to counter terrorism
Date: March 1, 2002
Creator: Stevens, W.; Michalske, T.; Trewhella, J.; Makowski, L.; Swanson, B.; Colson, S. et al.
Partner: UNT Libraries Government Documents Department