The electrical properties of semi-insulating (SI) Gallium Arsenide (GaAs) have been investigated for some time, particularly for its application as a substrate in microelectronics. Of late this material has found a variety of applications other than as an isolation region between devices, or the substrate of an active device. High resistivity SI GaAs is increasingly being used in charged particle detectors and photoconductive semiconductor switches (PCSS). PCSS made from these materials operating in both the linear and non-linear modes have applications such as firing sets, as drivers for lasers, and in high impedance, low current Q-switches or Pockels cells. In the non-linear mode, it has also been used in a system to generate Ultra-Wideband (UWB) High Power Microwaves (HPM). The choice of GaAs over silicon offers the advantage that its material properties allow for fast, repetitive switching action. Furthermore photoconductive switches have advantages over conventional switches such as improved jitter, better impedance matching, compact size, and in some cases, lower laser energy requirement for switching action. The rise time of the PCSS is an important parameter that affects the maximum energy transferred to the load and it depends, in addition to other parameters, on the bias or the average field …

From 1958, General Atomics maintain a hot cell facility in support of government-funded research into reactor fuels. As the use of the facility declined, General Atomics entered into an agreement with DOE to dismantle the facility and decontaminate and decommission (D&D) the site so that it could made available for unrestricted use. The Environmental Survey and Site Assessment Program (ESSAP) was requested to verify the final radiological status of the D&D effort. This is the report of ESSAP survey and verification activities conducted at the San Diego site from November 1999 through March 2000.

A research program to investigate the performance and potential for failure of Service Level 1 coating systems used in nuclear power plant containment is in progress. The research activities are aligned to address phenomena important to cause failure as identified by the industry coatings expert panel. The period of interest for performance covers the time from application of the coating through 40 years of service, followed by a medium-to-large break loss-of-coolant accident scenario, which is a design basis accident (DBA) scenario. The interactive program elements are discussed in this report and the application of these elements to the System 5 coating system (polyamide epoxy primer, carbon steel substrate) is used to evaluate performance.

Preliminary Monte Carlo simulations have demonstrated that passive Nuclear Materials Identification System (NMIS) measurements can be used to determine the mass of Pu in AT400-R containers with measurement times as short as a few minutes. The sensitivity of the proposed detectors to gamma rays should enhance this measurement method because the gamma rays from fission, induced or spontaneous, escape this container more easily than neutrons. In these calculations, the container contained two Pu spheres with mass varying between 0.5 and 2 Kg with {approximately}6 wt% {sup 240 }Pu.

The results of high temperature solubility studies at ORNL are presented in which mainly direct pH measurements were made of aqueous solutions in contact with the crystalline solid phases: Al(OH){sub 3}, AlOOH, Fe{sub 3}O{sub 4}, Mg(OH){sub 2}, Nd(OH){sub 3}, and ZnO. Examples are highlighted of specific phenomena such as: the kinetics of gibbsite and boehmite dissolution and precipitation; the appearance of metastable equilibria in the dissolution of Fe{sub 3}O{sub 4}; the extremely rapid precipitation of crystalline brucite, Mg(OH){sub 2}; and anomalies in the apparent solubility profiles of AlO(OH) and ZnO. General trends associated with the effects of temperature and ionic strength are mentioned. Some of the potentiometric investigations were augmented by conventional batch [AlO(OH) and ZnO], and flow-through column (ZnO) experiments. In the additional case of ZnCr{sub 2}O{sub 4}, the extremely low solubility of this spinel permitted application of only the latter technique and these results are discussed in terms of the measured chromium levels that resulted from incongruent dissolution.

An advanced statistical model is presented, which describes the SBS of a randomized laser beam interacting with an underdense, expanding plasma. The model accounts for the self-focusing of speckles and for its influence on the speckles SBS reflectivity in the regime where the effect of plasma heating is important. Plasma heating has an important effect on speckle self-focusing and it decreases the SBS threshold and also decreases the SBS reflectivity. The model exhibit a good agreement with the measured SBS levels at the LULI multi-beam facility for a broad range of the laser and plasma parameters and both types of beam smoothing--RPP and PS. Both the model and the experiments confirm that the PS technique allows to control the SBS level more efficiently than RPP.

The document collects information from field instrumentation, laboratory tests, and analytical models to provide a single source of information on the chemistry of flammable gas generation at the Hanford Site. It considers the 3 mechanisms of formation: radiolysis, chemical reactions, and thermal generation. An assessment of the current models for gas generation is then performed. The results are that the various phenomena are reasonably understood and modeled compared to field data.

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The current state of knowledge of the effect of plutonium on microorganisms and microbial activity is reviewed, and also the microbial processes affecting its mobilization and immobilization. The dissolution of plutonium is predominantly due to their production of extracellular metabolic products, organic acids, such as citric acid, and sequestering agents, such as siderophores. Plutonium may be immobilized by the indirect actions of microorganisms resulting in changes in Eh and its reduction from a higher to lower oxidation state, with the precipitation of Pu, its bioaccumulation by biomass, and bioprecipitation reactions. In addition, the abundance of microorganisms in Pu-contaminated soils, wastes, natural analog sites, and backfill materials that will be used for isolating the waste and role of microbes as biocolloids in the transport of Pu is discussed.

A shock tube coupled to a time-of-flight mass spectrometer has been employed to analyze the dynamic behavior of reactants, products, and intermediates in those reaction systems which are most pertinent to understanding the chemistry attendant to the soot formation process. The measurement of the decay rates of the reactants, the rate of formation of intermediates and products have been used to determine rate constants over a wide temperature range. Recent examples include the pyrolyses of allene, propyne, pyrazine, pyrimidine, pyridine, acetylene, furan, cyclopentadiene, and methylcyclopentadiene.

The final project period was devoted to investigating the binary mixture pyrolysis of polypropylene and polystyrene. Their interactions were assessed in order to provide a baseline for experiments with multicomponent mixtures of polymers with coal. Pyrolysis of polypropylene, polystyrene and their binary mixture was investigated at temperatures of 350 C and 420 C with reaction times from 1 to 180 minutes. Two different loadings, 10 mg and 20 mg, were studied for neat polypropylene and polystyrene to assess the effect of total pressure on product yields and selectivities. For neat pyrolysis of polypropylene, total conversion was much higher at 420 C, and no significant effect of loading on the total conversion was observed. Four classes of products, alkanes, alkenes, dienes, and aromatic compounds, were observed, and their distribution was explained by a typical free radical mechanism. For neat polystyrene pyrolysis, conversion reached approximately 75% at 350 C, while at 420 C the conversion reached a maximum around 90% at 10 minutes and decreased at longer times because of condensation reactions. The selectivities to major products were slightly different for the two different loadings due to the effect of total reaction pressure on secondary reactions. For binary mixture pyrolysis, the overall …

Numerical modeling of the urban boundary layer is complicated by the need to describe airflow patterns outside of the computational domain. These patterns have an impact on how successfully the simulation is able to model the turbulence associated with the urban boundary layer. This talk presents experiments with the model boundary conditions for simulations that were done to support two Department of Energy observational programs involving the Salt Lake City basin. The Chemical/Biological Non-proliferation Program (CBNP) is concerned with the effects of buildings on influencing dispersion patterns in urban environments. The Vertical Transport and Mixing Program (VTMX) investigating mixing mechanisms in the stable boundary layer and how they are influenced by the channeling caused by drainage flows or by obstacles such as building complexes. Both of these programs are investigating the turbulent mixing caused by building complexes and other urban obstacles.