Laser ablation is effective both as an analytical tool and as a means of removing surface coatings. The elemental composition of surfaces can be determined by either mass spectrometry or atomic emission spectroscopy of the atomized effluent. Paint can be removed from aircraft without damage to the underlying aluminum substrate, and environmentally damaged buildings and sculptures can be restored by ablating away deposited grime. A recent application of laser ablation is the removal of radioactive contaminants from the surface and near-surface regions of concrete. We present the results of ablation tests on concrete samples using a high power pulsed Nd:YAG laser with fiber optic beam delivery. The laser-surface interaction was studied on various model systems consisting of Type I Portland cement with varying amounts of either fine silica or sand in an effort to understand the effect of substrate composition on ablation rates and mechanisms. A sample of non-contaminated concrete from a nuclear power plant was also studied. In addition, cement and concrete samples were doped with non-radioactive isotopes of elements representative of cooling waterspills, such as cesium and strontium, and analyzed by laser-resorption mass spectrometry to determine the contamination pathways. These samples were also ablated at high power to …

A series of electroactive spinel compounds, LiMn{sub 2{minus}x}Cu{sub x}O{sub 4} (0.1 {le} x {le} 0.5) has been studied by crystallographic, spectroscopic and electrochemical methods and by electron-microscopy. These LiMn{sub 2{minus}x}Cu{sub x}O{sub 4} spinels are nearly identical in structure to cubic LiMn{sub 2}O{sub 4} and successfully undergo reversible Li intercalation. The electrochemical data show a remarkable reversible electrochemical process at 4.9 V which is attributed to the oxidation of Cu{sup 2+} to Cu{sub 3+}. The inclusion of Cu in the spinel structure enhances the electrochemical stability of these materials upon cycling. The initial capacity of LiMn{sub 2{minus}x}Cu{sub x}O{sub 4} spinels decreases with increasing x from 130mAh/g in LiMn{sub 2}O{sub 4} (x=0) to 70 mAh/g in ''LiMn{sub 1.5}Cu{sub 0.5}O{sub 4}'' (x=0.5). The data also show slight shifts to higher voltage for the delithiation reaction that normally occurs at 4.1 V in standard Li{sub 1{minus}x}Mn{sub 2}O{sub 4} electrodes (1 {ge} x {ge} 0) corresponding to the oxidation of Mn{sup 3+} to Mn{sup 4+}. Although the powder X-ray diffraction pattern of ''LiMn{sub 1.5}Cu{sub 0.5}O{sub 4}'' shows a single-phase spinel product, neutron diffraction data show a small, but significant quantity of an impurity phase, the composition and structure of which could not be identified. X-ray …

The stacking of second and third layers of supercrystals of self-assembled passivated gold nanoparticles has been investigated using transmission electron microscopy. We report for the first time nanoparticles occupying the twofold saddle site in the third layer.

Evapotranspiration is an essential component of the surface hydrological balance, but obtaining accurate estimates of the water vapor flux over large terrestrial areas can be difficult because of the substantial temporal and spatial variability in surface moisture conditions that can occur. This variability is often very large in the Great Plains and other portions of the Mississippi River Basin. Nevertheless, variations in soil moisture content, groundwater levels, and runoff in streams and rivers cannot be fully assessed without some knowledge of evapotranspiration rates. Here, observations made at the Walnut River Watershed (WRW), which is near Wichita, Kansas, and has an area of approximately 5000 km{sup 2}, are used to improve and test a modeling system that estimates long-term evapotranspiration with use of satellite remote sensing data with limited surface measurements. The techniques may be applied to much larger areas. As is shown in Fig. 1, the WRW is located in the Red River Basin and is enclosed by the southern Great Plains Clouds and Radiation Testbed (CART) of the US Department of Energy's Atmospheric Radiation Measurement (ARM) program. The functional relationships involving the satellite data, surface parameters, and associated subgrid-scale fluxes are modeled in this study by the parameterization of …

This Paper develops a statistical strength theory for three-dimensionally (3-D) oriented short-fiber reinforced composites. Short-fiber composites are usually reinforced with glass and ceramic short fibers and whiskers. These reinforcements are brittle and display a range of strength values, which can be statistically characterized by a Weibull distribution. This statistical nature of fiber strength needs to be taken into account in the prediction of composite strength. In this paper, the statistical nature of fiber strength is incorporated into the calculation of direct fiber strengthening, and a maximum-load composite failure criterion is adopted to calculate the composite strength. Other strengthening mechanisms such as residual thermal stress, matrix work hardening, and short-fiber dispersion hardening are also briefly discussed.

As part of the China-MAP program, sponsored by the US National Aeronautics and Space Administration, regional inventories of air pollutants emitted in China are being characterized, in order that the atmospheric chemistry over China can be more fully understood and the resulting ambient concentrations in Chinese cities and the deposition levels to Chinese ecosystems be determined with better confidence. In addition, the contributions of greenhouse gases from China and of acidic aerosols that counteract global warming are being quantified. This paper presents preliminary estimates of the emissions of some of the major air pollutants in China: sulfur dioxide (SO{sub 2}), nitrogen oxides (NO{sub x}), carbon monoxide (CO), and black carbon (C). Emissions are estimated for each of the 27 regions of China included in the RAINS-Asia simulation model and are subsequently distributed to a 1{degree} x 1{degree} grid using appropriate disaggregation factors. Emissions from all sectors of the Chinese economy are considered, including the combustion of biofuels in rural homes. Emissions from larger power plants are calculated individually and allocated to the grid accordingly. Data for the period 1990-1995 are being developed, as well as projections for the future under alternative assumptions about economic growth and environmental control.

Soil moisture content is a crucial variable in studies of hydrology, meteorology, and plant sciences. Soil moisture content influences the ability of land to hold additional water from precipitation and thus affects groundwater levels and runoff. Evapotranspiration rates are strongly influenced by soil moisture content near the surface; evapotranspiration regulates surface air temperature and is a major factor in modifying the water vapor content of the atmosphere. Adequate soil moisture is essential for plant growth; excesses and deficits of soil moisture must be considered in agricultural management practices. Soil moisture can be measured by a variety of in situ techniques, but such techniques often are inadequate for evaluation over large areas because of strong temporal and spatial variations. Here, a technique using standard surface meteorological observations together with remote sensing data from satellites is discussed.

Lasers plasma instabilities are an important constraint in x-ray driven inertial confinement fusion. In hohlraums irradiated with 1.06 {mu}m light on the Shiva laser, plasma instabilities were extremely deleterious, driving the program to the use of shorter wavelength light. Excellent coupling has been achieved in hohlraums driven with 0.35 {mu}m light on the Nova laser. Considerable attention is being given to the scaling of this excellent coupling to the larger hohlraums for an ignition target. Various instability control mechanisms such as large plasma wave damping and laser beam incoherence are discussed, as well as scaling experiments to check the instability levels.

Simulation of hypersonic flight in ground test and evaluation (T and E) facilities is a challenging and formidable task, especially to fully duplicate the flight environment above approximately Mach 8 for most all hypersonic flight systems that have been developed, conceived, or envisioned. Basically, and for many years, the enabling technology to build such a ground test wind tunnel facility has been severely limited in the area of high-temperature, high-strength materials and thermal protection approaches. To circumvent the problems, various approaches have been used, including partial simulation and use of similarity laws and reduced test time. These approaches often are not satisfactory, i.e. operability and durability testing for air-breathing propulsion development and thermal protection development of many flight systems. Thus, there is a strong need for science and technology (S and T) community involvement in technology development to address these problems. This paper discusses a specific case where this need exists and where significant S and T involvement has made and continues to make significant contributions. The case discussed will be an Air Force research program currently underway to develop enabling technologies for a Mach 8-15 hypersonic true temperature wind tunnel with relatively long run time. The research is based …

Experiments have been performed using a coaxial end-effecter to combine a focused laser beam and a plasma arc. The device employs a hollow tungsten electrode, a focusing lens, and conventional plasma arc torch nozzles to co-locate the focused beam and arc on the workpiece. Plasma arc nozzles were selected to protect the electrode from laser generated metal vapor. The project goal is to develop an improved fusion welding process that exhibits both absorption robustness and deep penetration for small scale (< 1.5 mm thickness) applications. On aluminum alloys 6061 and 6111, the hybrid process has been shown to eliminate hot cracking in the fusion zone. Fusion zone dimensions for both stainless steel and aluminum were found to be wider than characteristic laser welds, and deeper than characteristic plasma arc welds.

The authors have directly measured the stress evolution during metal organic chemical vapor deposition of AlGaN/GaN heterostructures on sapphire. In situ stress measurements were correlated with ex situ microstructural analysis to directly determine a critical thickness for cracking and the subsequent relaxation kinetics of tensile-strained Al{sub x}Ga{sub 1{minus}x}N on GaN. Cracks appear to initiate the formation of misfit dislocations at the AlGaN/GaN interface, which account for the majority of the strain relaxation.

The Waste Isolation Pilot Plant (WIPP) project was undertaken in response to the growing need for a national repository for transuranic (TRU) waste. Guidelines for WIPP specify that any waste item to be interred must be fully characterized and analyzed to determine the presence of chemical compounds designated hazardous and certain toxic elements. The Transuranic Waste Characterization Program (TWCP) was launched to develop analysis and quality guidelines, certify laboratories, and to oversee the actual waste characterizations at the laboratories. ORNL is participating in the waste characterization phase and brings to bear a variety of analytical techniques including ICP-AES, cold vapor atomic absorption, and instrumental neutron activation analysis (INAA) to collective determine arsenic, cadmium, barium, chromium, mercury, selenium, silver, and other elements. All of the analytical techniques involved participate in a cooperative effort to meet the project objectives. One important component of any good quality assurance program is determining when an alternate method is more suitable for a given analytical problem. By bringing to bear a whole arsenal of analytical techniques working toward common objectives, few analytical problems prove to be insurmountable. INAA and ICP-AES form a powerful pair when functioning in this cooperative manner. This paper will provide details of …

Recent interest in delayed neutron parameters including comparisons between macroscopic (experimental) and microscopic (calculated) results have prompted a set of experiments using the 1MW Triga Reactor at the Texas A and M University (TAMU) Nuclear Science Center (NSC) designed to measure the complete set of seven-group delayed neutron parameters for several higher actinides. Operating the Nuclear Science Center Reactor (NSCR) in a pulsed mode, a complete set of delayed neutron parameters were measured for Np-237 and Am-243. The total delayed neutron yield per 100 fissions for Np-237 and Am-243 was found to be 1.14 {+-} 0.07 and 0.85 {+-} 0.05, respectively. Comparisons to previous measurements are made where such measurements are available.

A radioactive ion beam facility - in short a RIB facility - produces ions of short-lived nuclei and accelerates them to energies of 0.1�10 MeV per nucleon or even higher. In this process it is important that the resulting RIB beams are free from nuclei of neighboring isobars or of neighboring elements. This task requires the production and ionization of the nuclei of interest as well as separating them from all others with a high-mass resolving power and small-mass cross contaminations. When constructing such a facility it also is very important to find ways that allow the accelerated ions to be provided to different experiments at least quasi simultaneously.

A multi-sample Cs sputter negative-ion source, equipped with a conical-geometry, W-surface-ionizer has been designed and fabricated that permits sample changes without disruption of on-line accelerator operation. Sample changing is effected by actuating an electro-pneumatic control system located at ground potential that drives an air-motor-driven sample-indexing-system mounted at high voltage; this arrangement avoids complications associated with indexing mechanisms that rely on electronic power-supplies located at high potential. In-beam targets are identified by LED indicator lights derived from a fiber-optic, Gray-code target-position sensor. Aspects of the overall source design and details of the indexing mechanism along with operational parameters, ion optics. intensities, and typical emittances for a variety of negative-ion species will be presented in this report.

Chemically active radioactive species, diffused from RIB target materials, often arrive at the ionization chamber of the source in a variety of molecular forms. Because of the low probability for simultaneously dissociating and efficiently ionizing the individual atomic constituents of molecules with conventional hot-cathode electron-impact ion sources, the species of interest are often distributed in several mass channels in the form of molecular side-band beams and consequently, their intensities are diluted. The sputter negative ion beam generation technique offers an efficient means for simultaneously dissociating and ionizing highly electronegative atomic species present in molecular carriers. We have incorporated these principles in the design and fabrication of a kinetic ejection negative ion source and evaluated its potential for generating {sup 17,18}F{sup {minus}} beams for the Holifield Radioactive Ion Beam Facility astrophysics research program. The source utilizes Cs{sup +} beams to bombard condensable fluorine compounds that emanate from a target material, such as Al{sub 2}O{sub 3}, and are transported to the cooled inner surface of a conical-geometry cathode where they are adsorbed. The energetic Cs{sup +} beams efficiently dissociate these molecules and sputter their constituents. Since the work functions of cesiated surfaces are low, highly electronegative species such as fluorine are efficiently …

The U.S. Nuclear Science Community in its 1996 Long Range Plan identified an advanced radioactive ion beam (RIB) facility based on the ISOL technique as the next major facility to be constructed for U.S. nuclear physics. The proposed SpaHation Neutron Source (SNS) for Oak Ridge National Laboratory, whose construction design funds have recently been appropriated, offers a unique opportunity for the construction of this new facility, Plans for extracting a proton beam from the SNS, transporting it to the RIB facility, and constructing the new RIB facility at the SNS site are discussed, as are the ISOL targets, radiation handling, isobaric separation, acceleration of beams of radioactive experimental areas.

New techniques for enhancing the performances of electron cyclotron resonance (ECR) ion sources are being investigated at the Oak Ridge National Laboratory. We have utilized the multiple discrete frequency technique to improve the charge state distributions extracted from conventional magnetic field geometry ECR source by injecting three frequencies into the source. A new flat central magnetic field concept, has been incorporated in the designs of a compact all-permanent-magnet source for high charge-state ion beam generation and a compact electromagnetic source for singly ionized radioactive ion beam generation for use in the Holifield Radioactive Ion Beam Facility (HRIBF) research program. A review of the three frequency injection experiments and descriptions of the design aspects of the "volume-type" ECR ion sources will be given in this report.

In this paper is described tests of EiChrom Industries' Ni-selective ion exchange resin for use in analysis of Ni-63 in Savannah River Site high level waste.

The technical challenge for making two-beam accelerators into realizable power sources for high-energy colliders lies in the creation of the drive beam and in its propagation over long distances through multiple extraction sections. This year we have been constructing a 1.2&A, l-MeV, induction gun for a prototype relativistic klystron two-beam accelerator (RK-TBA). The electron source will be a 8.9 cm diameter, thermionic, flat-surface cathode with a maximum shroud field stress of approximately 165 kV/cm. Additional design parameters for the injector include a pulse length of over 150-ns flat top (1% energy variation), and a normalized edge emittance of less than 300 pi-mm-n-n. The prototype accelerator will be used to study physics, engineering, and costing issues involved in the application of the RK-TBA concept to linear colliders. We have also been studying optimization parameters, such as frequency, for the application of the RK-TBA concept to multi-TeV linear colliders. As an rf power source the RK-TBA scales favorably up to frequencies around 35 GHz. An overview of this work with details of the design and performance of the prototype injector, beam line, and diagnostics will be presented.

This report describes efforts made at the oak Rklge NatiOnrd Laboratory to design high- efficiency-release targets that simultaneously incorporate the short diffusion lengths, high permeabilities, controllable temperatures, and heat-removal properties required for the generation of useful radioactive ion beam (RIB) intensities for nuclear physics and astrophysics research using the isotope separation on-line (ISOL) technique. Short diffusion lengths are achieved either by using thin fibrous target materials or by coating thin layers of selected target material onto low-density carbon fibers such as reticulated-vitreous-carbon fiber (RVCF) or carbon-bonded-carbon fiber (CBCF) to form highly permeable composite target matrices. Computational studies that simulate the generation and removal of primary beam deposited heat from target materials have been conducted to optimize the design of targetheat-sink systems for generating RIBs. The results derived from diffusion release-rate simulation studies for selected targets and thermal analyses of temperature distributions within a prototype targetlheat-sink system subjected to primary ion beam irradiation will be presented in this report.

An operational evaluation of the Integrated Solar Upper Stage (ISUS) power management and distribution (PMAD) system was conducted as part of the Engine Ground Demonstration thermionic power system test program-- START-3. START-3 testing took place at the Baikal Test Stand, located in the University of New Mexico's Energy Conversion Research Laboratory at the New Mexico Engineering Research Institute in Albuquerque, NM. One objective of this test was to evaluate the operational performance of the lSUS PMAD system developed by the National Aeronautics and Space Administration (NASA) Lewis Research Center. Tests of the PMAD with the ISUS diode string demonstrated that the PMAD could regulate the output of an array of thermionic converters within the design requirements and couId be modified to optimize performance for diode strings of fewer than 16 diodes.

This paper provides an overview of the Worker Protection System (WPS), a client/server, Windows-based database management system for essential radiological protection and industrial hygiene. Seven operational modules handle records for external dosimetry, bioassay/internal dosimetry, sealed sources, routine radiological surveys, lasers, workplace exposure, and respirators. WPS utilizes the latest hardware and software technologies to provide ready electronic access to a consolidated source of worker protection.

A number of questions remain concerning homogeneous aerosol formation by natural organics interacting with anthropogenic pollutants. For example, chlorine has been proposed as a potential oxidant in the troposphere because of its very high reactivity with a wide range of organics (Finlayson-Pitts, 1993). Indeed, sea salt aerosol in the presence of ozone has been shown to produce chlorine atoms in heterogeneous photochemical reactions under laboratory conditions. Whether chlorine can initiate oxidation of natural organics such as monoterpene hydrocarbons and can generate homogeneous nucleation or condensable material that contributes to aerosol loadings needs to be assessed. The nighttime reactions of ozone and nitrate radical can also result in monoterpene reactions that contribute to aerosol mass. We are currently planning field studies in Puerto Rico to assess these aerosol issues and other atmospheric chemistry questions. Puerto Rico has a number of key features that make it very attractive for a field study of this sort. The principal feature is the island's very regular meteorology and its position in the Caribbean Sea relative to the easterly trade winds. This meteorology and the island's rectangular shape (100 x 35 miles) make it highly suitable for simplification of boundary layer conditions. In addition, the long …