A high-temperature crystal growth experiment produced discrete singlecrystal products of Allr and IrSi. The preparation, and examination of these phases is described within. This project is part of a materials compatibility study relating to radioisotopic heat sources. These heat sources are comprised of a PuO2 fuel pellet encapsulated in an Ir alloy containment shell. Thorium is introduced as an additive within the Ir to maintain ductility. Si and P are picked up inadvertently in the fuel processing. The compatibility of the heat sources with Al is of interest because of potential interactions with the Al alloy hardware associated with the heat source environment.

Texture, i.e. preferred orientation (PO), of crystallites can cause serious systematic errors in quantitative analysis of crystalline materials using x-ray powder diffraction (XRPD) data. The singleparameter model of March (1932), proposed by Dollase (1986) for use in powder diffractometry is a promising mathematical formalism for correcting PO in XRPD analysis of uniaxially-oriented specimens. O'Connor et al. (1991) successfully applied the March formula in applying preferred orientation corrections for gibbsites, Al(OH)3, using Rietveld pattern-fitting and a line ratio method in which corrections are determined according to the intensity ratios of selected lines. The paper gives an appraisal of the general applicability of the methods considered by Li and O'Connor with particular reference to powder diffraction data for gibbsite, molybdite (MoO3), calcite (CaCO3) and kaolinite specimens. It is shown that some caution should be exercised when using the March formula to describe PO in Rietveld analysis.

This paper corrects assumptions made by previous authors regarding the magnitude of the error in d-versus-sin2ѱ plots resulting from deviations of the sample surface from the focusing circle. The results show that the effect is not significant for ordinary residual stress measurements. This investigation has also shown that shapes in d-versus- sin2ѱ plots, similar to the sample curvature effect, may exist in samples with large residual stresses. Interpretation of the data should consider the magnitude of the apparent stress, which allows one to distinguish between apparent sample curvature effects and other causes.

Slow data acquisition rates have, in the past, limited the use of X-ray diffraction for characterization of polymeric materials. Photon counting techniques yield quantitative data in digital form for computer analysis. However, a great deal of data acquisition time is required when data is taken sequentially; i.e., when each intensity determination (at a particular goniometer setting) requires a separate time interval, during which intensity at other angle values is ignored. The problem is particularly acute for oriented polymers since two or more diffraction angles are involved: The Bragg angle along with at least one orientation angle. For this reason, an area-imaging (two-dimensional) proportional counter has been developed for use with a four-circle X-ray diffraction system. Although basically a single-crystal unit, this goniometer has been used in this laboratory and others for studies of oriented polymers. The receiving pinhole collimator and aperture have been removed, and the area-imaging counter has been mounted on the detector arm track. The original receiving aperture is still used for alignment, and the area detector Is positioned with its center at the receiving aperture center position.

The role of statistics in certain areas of X-ray fluorescence analysis is considered. The topics discussed include: calculating the standard deviation associated with the result of an analysis; optimizing experimental parameters for both wavelength and energy dispersive analyses; evaluating limits of detection, limits of decision, and limits of determination; and weighting in the least squares fitting of data in single element polynomial relationships and in multi-element multiple regression analysis.

For the generation of high temperatures in X-ray and neutron diffraction experiments various techniques such as resistance heating, radiation heating, induction heating and gas flame heating have been applied (Aldebert, 1984). Mirror heaters usually employ some kind of focussing geometry to concentrate the radiation emanating from the heating element onto the sample: Two large parabolic mirrors focussing heat radiation from a carbon arc were used by Stecura (1968) to reach sample temperatures up to 1700°C. Hubert et al. (1974) used radiation from a short arc xenon lamp focussed by two parabolical mirrors to reach sample temperatures of 3200°C.

The statistical fluctuations of photon counts arediscussedas a factor limiting the precision of the analytical result. Assuming a Poisson distribution, the theoretical standard deviation of the result can be calculated. While this prediction does not consider causes of variation other than the count statistics, it is useful in developing methods and checking instrument reliability. Practical examples using experimental results are given.

Synchrotron radiation was used to obtain a high-resolution powder diffraction pattern of the high-density form of BeH2, a material whose unit-cell dimensions have not previously been determined. The observed d-spacing values were presented to three different computer indexing programs. All three programs returned as best solution a body-centered orthorhombic unit cell with a = 9.082, b = 4.160, c = 7.707 Å and V = 292 Å3. Interpretation of the three-dimensional Patterson led to 12 BeH2 molecules per unit cell; thus, the theoretical density is 0.755 g/cm3. The molecular structure is based on a network of corner-sharing BeH4 tetrahedra rather than flat, infinite chains with hydrogen bridges previously assumed.

As early as 1974 cracking was observed in the austenitic stainless steel piping systems of several Boiling Water Reactors [1,2]. Failure analysis indicated that the cracks developed through intergranular stress-corrosion cracking and an active interest in residual stress measurement methodologies developed. This paper describes the procedures and demonstration testing employed to provide absolute residual stress measurement, nondestructively, on the inside surface of pipe specimens. A Ruud-Barrett position sensitive detector (PSSD)* was used to build an EPRI pipe stress analyzer which was developed for these residual stress measurements [3,4].

The work describes a method for determining the orientation of crystallographic planes in thin samples using both asymmetric Bragg reflection and asymmetric Laue transmission method.

The method is based on the extension of a system of nonlinear equations for the reflection case. The solutions of the system of nonlinear equations in question can be positive, negative or mixed with physical significance. The positive solutions correspond to reflection case, while the negative solutions are for transmission case. The mixed solutions were generated for the planes {111} in a cubic structure.

A theoretical test is given for a silicon sample. The results are in good agreement with the experimental results given in literature.

A technique is described for the study of the early stages of precipitation hardening in single-crystalline and poly crystalline copperberyllium alloys. Since no trace of the equilibrium precipitate responsible for hardening can be detected by ordinary X-ray or metallographic techniques prior to the onset of overaging, the described method is based on the changes produced in the matrix as the result of the formation of aggregates along preferred lattice planes. Such formations produce accommodation strains in the matrix lattice which, can be detected as a change in the intensity and angular range of matrix reflection.

An interpretation of the age hardening sequence in a copper - beryllium, alloy after isothermal annealing is presented in terms of fundamental transformations.

The characteristic 17.441 keV Mo-Kα tube line yields an exceedingly strong reflection at a Bragg angle of 6.0710 on Highly Oriented Pyrolytic Graphite (IIOPG). Using doubly bent toroidally shaped crystals we were able to concentrate the characteristic radiation from a Mo anode fine focus tube onto a small focal spot area of about 1 mm. FWHM diameter, as was observed by an X-Ray sensitive CCD. The radiation of the Mo anode fine focus tube is emitted at a take-off angle of 60 into a total solid angle with an aperture of 120. About 90 percent of this primary radiation solid angle can be used for the desired Bragg reflection on the designed toroidal crystal surface. This feature ensures the high beam intensity needed for special excitation problems.

X-ray emission spectra have been obtained with a single crystal spectrometer having a resolution λ/dλ of 6,640 for iron Kβ5 spectra. The spectrometer consisted of a Jarrel-Ash Microfocus unit in conjunction with a Picker diffractometer which was operated as a rocking crystal spectrometer with a stepping angle of 1/400th of a degree. Kβ5 and Kβ1,3 spectra have been obtained from iron, Fe0.9Mn0.9Ge, Fe1.60Ge, FeGe, FeGe2 and germanium. Because the K05 spectra are due to 4p - Is transitions from the 3d bands, the Kβ5 intensities are a direct measure of the overlap or hybridization of the 3d - 4s - 4p bands. The experimental results can be correlated either with orbitals derived on the basis of coordination, or more roughly with possible band distributions.

Spectrographic analysis for carbon and boron using fluorescent x-rays has been studied over the past few years; principles and applications for using those ultra-soft x-rays were described, based on the combination of total reflection and filtering rather than on the wavelength dispersive method of Bragg reflection (1, 2). However, oxygen and nitrogen, with x-ray wavelengths of 23.7lÅ and 31.60Å, respectively, cannot be detected as easily because of their high absorption by the detector window materials such as polypropylene, polyester or formvar films.

HFIT is a program for the analysis of diffraction diagrams containing overlapping peak clusters. Profile functions have been implemented to analyze synchrotron diffraction data. It is written un Turbo C++ for PC operations. The analysis is done by operator interaction. The analysis is done on sections of the diffractogram containing a maximum of 2048 data points or 100 diffraction maxima. Special care is taken for smoothing the data and for the subtraction of background.

Residual stress measurements were made on a ground rail steel (0.75 %C) using the newly developed ϕ-integral method and the conventional ψ-differential method. The strains <εϕψ> were measured as a function of the azimuth angle ϕ, the angle of rotation about an axis perpendicular to the specimen surface, from 0° to 360° in steps of 15°, at fixed tilt angles ψ, the angle between the normals to the specimen surface and the reflecting planes (hkl), set between 0° and 45° in steps of 9°.

It was found that <εϕψ> plotted as a function of ϕ is not periodic with the period of 180° and consequently exhibits the so-called ψ-splitting when plotted as a function of sin2ψ at constant ϕ. The Fourier coefficients of the function <εϕψ> plotted versus ϕ were used to evaluate the strain tensor <εij> in the integral method. Assuming that isotropic elasticity theory is applicable, the stress tensor <σij> was calculated, and excellent agreement was found between the values determined with the ϕ integral and ψ-differential methods.

During recent years energy dispersive x-ray fluorescence (EDXRF) has been used to measure the elemental content of atmospheric aerosols. The code described here is used to reduce EDXRF data and determine the elemental composition of samples collected on membrane filters. The program has been specifically written for EDXRF analysis of size-fractionated aerosols collected by a dichotomous sampler.

The x-ray fluorescence spectrometer used in our laboratory employs a pulsed-mode x-ray tube and a lithium-drifted silicon detector. Pulse-height spectra are produced for elements ranging in atomic number from Z = 13 to Z = 82 (corresponding to an energy range from 1.4 to 32.1 keV). Approximately uniform x-ray production is attained by producing independent spectra from three secondary targets (Ti, Mo, Sm).

Todays demand for rapid trace element analysis in pollution control and resource materials has led to the development of a completely automatic, very sensitive and stable Si(Li) X-ray analyzer. The key element, a transmission target tube, which has inherently a very clean monochromatic X-ray output, has been studied in view of efficiency, sensitivity and stability. The transmission target tube requires different operating criteria than conventional X-ray tubes. An analysis was made to “explain” these differences using fundamental X-ray physics. Studies included various experiments directly applied to practical problems in analysis of pollutants and mineral resource materials.

In X-ray fluorescence analysis, the specific secondary radiation intensities of the elements are generated and measured by a spectrometer. Usually, the measured intensities are corrected for instrument drift first, then converted into element concentrations. In routine analysis, the intensity is always affected by the instability of the instrument. Instrumental instability consists of two components: short and long term drift Short-term instability is caused by fluctuations in the ambient laboratory conditions and the instrument's components. Long-term drift is caused by aging of the instrument's components (mainly X-ray tube, crystals, detectors, electronic circuitry) and results in a gradual intensity decrease. For example, the X-ray tube output decreases due to pitting of the target and sublimation of metal on the inside of the window. The quantum efficiency of detectors gradually decreases due to drift in potential supply and changes in ambient pressure and temperature.

A feasibility test at the Naval Research Laboratory has shown that a miniature X-ray Fluorescence (XRF) sensor can be constructed for the cone penetrometer. Such a sensor would have detection limits for heavy metal contaminants in soils of a few parts per million. The next step is to demonstrate the capabilities of such a sensor in the cone penetrometer. A sensor for this purpose is being constructed and will be tested both in the laboratory and in the field. The XRF sensor will be capable of evaluating the in-situ detection limits and field screening (semi-quantitative) capabilities of x-ray fluorescence and can be transitioned to field activities for further evaluation and feedback. The sensor will consist of a miniature x-ray tube and an x-ray detector, together with appropriate apertures and x-ray filters, in a custom fabricated section of penetrometer pipe. The sensor will use commercially available components. High voltage and signal cables will couple the sensor to electronics in the truck. Boron carbide will be used for the x-ray windows which protect the sensor components from soil abrasion.