Monte Carlo simulation is used to determine the effects of selfabsorption for the low energy X-rays of light elements in the size range front 1 to 20 μm. Calculations are performed for a wide angle Fe-55 radioisotope-excited energy dispersive XRF system. Results are obtained for sulfur attenuation in thin layers, long cylinders, and spheres composed of various matrix materials. The enhancement effect is also treated for the transition region between thin and thick layer samples as well as in spheres of various sizes. Results are also comrpared to fixed angle analytical models.

Urea complexes consist of a channel made up of hydrogen-bonded urea host molecules into which a variety of guest molecules can fit to form a crystalline complex. The urea host can accommodate, one at a time, a variety of guests having the requisite size and shape. The stability of the resulting complex is a function of the properties of the guest molecule. A procedure has been devised which produces pure complex free of any uncomplexed urea or host molecules in solution. The insoluble crystalline complexes formed from the solution of urea and guest molecule in methanol established a dynamic equilibrium. When the crystals of complex are removed from the solution, dissociation to urea and guest occurs to an extent, depending upon the dissociation constant of the complex. If the dissociation constant, KD, is very low, undetectable quantities of uncomplexed urea form along with complex. If the dlissoclation constant is high, extensive amounts of urea form in the presence of complex. Characteristic interplanar spacing s are obtained for a urea complex irrespective of the guest molecule present. The pattern obtained for the hexagonal complex is completely different from the pattern obtained for tetragonal urea. X-ray examination of a homologous series of compounds gives, for each partially dissociated complex, spacings for both urea and complex. The relative intensities of urea and complex spacings permit the estimation of the stability of such a complex compared to that of other homologues.

Asymmetric crystal topography (ACT) in reflection and transmission electron microscopy (TEM) were used to investigate the crystal quality of both typical GaAs substrates and AIGaAs epitaxial layers grown on these substrates. ACT topographs of large sections of 75mm GaAs wafers revealed the presence of several types of crystal defects. All the GaAs wafers surveyed showed the presence of low angle grain boundaries which usually extended over a significant portion of the wafer. In addition, the well-known cell structure dislocation network was always observed in semi-insulating wafers. Less common but often present were inclusions and precipitates. The n-type (Si doped) substrates showed a typical cross-hatched pattern. ACT topography also easily revealed the crystal damage caused by wafer grinding.

Epitaxial layers of AIGaAs were grown by conventional molecular beam epitaxy on these characterized GaAs substrates. ACT topography was used to examine separately the epitaxial layers and substrate crystals. Layers which were grown below the pseudomorphic limit showed crystal features identical to the GaAs substrate on which they were grown and the substrate was unaffected by the presence of the epitaxial layer. AJAs layers which were grown above the pseudomorphic limit were severely dislocated: TEM confirmed the presence of misfit dislocations at the interface. The substrate in this case also showed the presence of crosshatching indicating the the extension of the dislocation strain field into the substrate.

Determination of 35 trace and 8 major elements in a granitic rock by nondestructive X-ray emission and fast-neutron activation methods has been accomplished. Trace elements arsenic, barium, cadmium, cerium, cobalt, chromium, cesium, copper, gallium, gadolinium, germanium, hafnium, mercury, indium, lanthanum, molybdenum, manganese, niobium, neodymium, nickel, rubidium, antimony, scandium, samarium, tin, strontium, tantalum, thorium, titanium, vanadium, yttrium, ytterbium, zinc, and zirconium and major elements aluminum, calcium, iron, potassium, and silicon have been estimated in the vacuum X-ray spectrograph. Phosphorus has been excited by a chromium-target tube. Major elements magnesium, sodium, and oxygen have been estimated by the Henke aluminumtarget X-ray spectrograph. Major elements oxygen and silicon have also been determined by fast-neutron activation. Detection limits for traces are in cur system in the range of 1 to 100 ppm with standard deviations of about 1 to 10 ppm. Precision in the determination of major constituents is better than 1% in relative standard deviation. The data are reported in parts per million for the trace elements and for the major elements as well. It is suggested that this type of repotting of geochemical data be preferred to the conventional reporting of major constituents as oxides.

Additive elements are now included in manufacturing specifications for greases. Texaco uses X-ray fluorescence at lubricants manufacturing locations; however, analyses of greases in the neat form are difficult due to problems with uniform and repeatable filling of sample cups and outgassing of greases during measurements. This preparation procedure allows quantitative determinations of additive elements in a variety of greases using a single analytical program. Having a single method for all greases is important at busy manufacturing locations.

The preparation method involves dilution of samples in a binder powder. This approach eliminates outgassing and overcomes differences among greases such as type of soap, presence of MoS2 and graphite, and varying oil content. The powder absorbs oil and creates a uniform particle structure. Thorough mixing and careful cup packing yield repeatable measurements. The method allows the use of liquid oil standards for calibration, eliminating the need to obtain analyzed greases. Accurate calibrations have been created for both wavelength-dispersive and energy-dispersive spectrometers.

There are currently no plans for the commercial reprocessing of nuclear fuel in the U.S. This is not the case in Japan, England, France, Germany, or the USSR. The U.S. does, however, include the reprocessing of spent nuclear fuel as a part of its defense programs. The Office of Safeguards and Security of DOE's Defense Programs has funded the development and optimization of numerous nondestructive analysis techniques including K-edge x-ray fluorescence analysis. This paper reviews some of the implementation efforts resulting from R&D supported by that office.

In 1979, the concept of using K-edge x-ray fluorescence analysis (K XRFA) for the analysis of actinide solution concentrations was first presented. K XRFA using small radioactive Co-57 sources has been shown to be a practical way to measure actinide solution concentrations in offline, at-line, or on-line configurations. The experimental methodology is elegant and the hardware is simple.

The study of the mechanical behaviour of materials by X-ray measurements in a classical laboratory is limited by the possibilities of the X-ray tubes used. Some crystallographic planes are not conducive to good diffraction conditions and the radiation characteristics' may not be optimum. The use of synchrotron radiation resolves many of these problems by providing a continuously variable wavelength which allows measurements of stress and stress gradients to be carried out in very good conditions. The high intensity and perfectly monochromated radiation with a small beam divergence are very helpful for microstrain measurements.

XRD analysis of fly ash was quantitated using the Reference Intensity Ratio (RIR) method and rutile (TiO2) as an internal standard. Rutile RIR's for 15 of the crystalline phases commonly observed in North American fly ash were determined. Error analysis on the various steps in quantitation indicated that precision ranged from ±10% of the amount present for phases that diffract x-rays strongly to ±21% for weakly diffracting phases. Limit of detection in the mostly glassy fly ashes ranged from 0.2% for lime, the most strongly diffracting phase, to 3.5% for weakly diffracting mullite. Accuracy evaluated with a simulated fly ash was within the limits established by precision, but in actual fly ash samples, accuracy will be a function of the match between the crystallinity and composition of the analyte and the analyte standard. Overlaps among peaks of some of the important phases require intensity proportioning; for this reason, the method is best described as semi-quantitative.

Oscillations jn "d" vs. sin2ψ plots are due to the inhomogeneous partitioning of strains within the diffracting volume. In polycrystalline specimens, such inhomogeneity can be caused by the elastic incompatibility of neighboring grains or by the inhoniogeneous partitioning of plastic deformation within the diffracting volume. There is, however, little work on the degree of inhomogeneity required to cause a given oscillation, and the relative contribution from the elastic and plastic deformation components to a given oscillation.