Laser interaction experiments have been conducted on Sandia Laboratories' four-beam laser system. In these experiments, pulses of 1.06 μm light of up to 50 J each were focused in a tetrahedral geometry onto CD2 microspheres. A 22-channel x-ray spectrometer which utilises silicon diodes with appropriate K-edge prefilters was used for x-ray measurements. Typically, bremsstrahlung-recombination spectra were observed in the photon regime below about 5 keV. The electron temperatures for this part of the spectrum ranged from a few hundred eV to 1 keV with up to 15 percent of the total laser energy converted to x-rays. Less than one percent of the total energy emitted as x-rays appeared in the spectral range above 5 keV.

This paper presents the theoretical and practical aspects of measuring residual stresses by X-ray diffraction with emphasis on the analysis of aluminum alloys. The theoretical considerations of radiation) beam geometry, and peak location will be discussed in regard to establishing optimum analysis techniques. The precision and reproducibility of this technique have been investigated so that results can be applied accurately. The approach, however, is basically a practical one, with the intent of studying residual stress systems as they affect engineering applications. Residual stress systems produced by thermal and mechanical treatments have been determined and the effect of treatment modifications and variations on the resultant stress system have been analyzed. The effect of operational variables such as time and temperature on the developed stress system are shown. From this, the merits of a particular treatment can be determined with respect to its intended application.

Analysis of solution heat-treated and quenched 2014 aluminum has shown a significant effect of the quench temperature on the resultant residual stress system. The results obtained from shot-peening this alloy are presented, as well as the effect of time and temperature on the shot-peened stress gradient.

The ability to predict fatigue failure has long eluded scientists and engineers. Because they can be applied nondestructively, X-ray diffraction methods have been employed to measure fatigue induced lattice misorientation, lattice strain, residual stress and subgrain formation. The changes in the X-ray patterns, however, were found to be restricted principally to the very early and late fractions of the fatigue life. Their invariance during the intermediate portion of the life has hampered the evaluation of cumulative fatigue damage and prediction of ultimate failure.

The primary difference between previous investigations and our recent X-ray diffraction studies is the emphasis we placed on characterizing both the surface and subsurface response to fatigue. By evaluating the prefracture damage with depth from the specimen surface a more reliable procedure for failure estimation emerged.

An irradiation of solid samples with x-rays causes an electron emission from the sample surface, owing to photoabsorption. These electrons can be detected under vacuum conditions and are photo, Auger and secondary electrons. Due to inelastic collisions most of these electrons have lost some of their original kinetic energy along the path from the atom of origin to the surface. With nondispersive electron detection the total electron yield (TEY) is observed.

For measurements performed with a tunable x-ray monochromator information on the qualitative composition can be obtained by the following procedure. The photon energy has to be timed from below to above of one of the absorption edges of a given element. In case of its presence in the specimen an increase of the TEY-signal can be observed.

Several design concepts were evaluated for on-stream X-ray analysis, chief among which were: (1) sample presentation, (2) X-ray spectrograph and (3) data handling. The sample is presented to the X-ray spectrograph through a vertical cell having a mylar window and a device to measure variations in sample density. The X-ray spectrograph is of fixed-channel, modular design, with a capacity of up to six channels, and is designed for use in industrial environments. The complete spectrograph can be translated in a horizontal plane to position itself and determine the elemental composition in a series of sample cells. The data handling uses digital circuitry to permit normal use of analog readouts or digital data logging systems. Operational data are given for on-stream analysis.

Our experience using Mo Kα radiation in coal related research indicates that minerals can be detected and quantitatively measured at the 0.2% level in an amorphous substance such as coal. Since the linear absorption coefficient for most elements is about a factor of eight lower for Mo radiation than it is for Cu radiation, the matrix affect is greatly reduced and the intensity is a more linear function of concentration.

Although there is considerable overlapping of peaks when complex mixtures are analyzed using Mo radiation, the use of second derivative techniques to locate peaks, and least squares techniques to fit peaks can resolve many of these problems. The reduced time needed to collect a diffraction pattern, and the increased intensity obtained more than compensate for the extra computer time needed to analyze the data.

Two methods are described for computing multielement x-ray absorption corrections for aerosol samples collected in IPC-1478 and Whatman 4l filters. The first relies on scatter peak intensities and scattering cross sections to estimate the mass of light elements (Z < l4) in the sample. This mass is used -with the measured heavy element (Z ≥l4) masses to iteratively compute sample absorption corrections. The second method utilizes a linear function of ln(μ) vs. ln(E) determined from the scatter peak ratios and estimates sample mass from the scatter peak intensities. Both methods assume a homogeneous depth distribution of aerosol in a fraction of the front of the filters, and the assumption is evaluated with respect to an exponential aerosol depth distribution. Penetration depths for various real, synthetic and liquid aerosols were measured.

The production of standard x-ray diffraction patterns at NBS imposes special requirements in the data processing of powder patterns. The patterns should be complete and have an overall accuracy of better than 0.01 degree two theta. To ensure completeness all the observable peaks should be indexed. To make certain that the sample is a pure phase, weak peaks have to be identified as well.

The indexing of all the peaks implies that the cell constants must be known and there should be a good agreement between all the calculated and observed peak positions. In practice this is achieved by a least-squares refinement of the unit cell parameters. This serves as a test of the assumed unit cell and also as an interpretation of the observed peaks. Finally, an attempt is made to identify the space group. This step also requires the identification of weak peaks. The agreement of a known space group with the observed reflections further confirms the purity of the sample.

In the X-ray fluorescence analysis of homogeneous specimens, the correlation between the characteristic line intensity of an analyte element and the concentration of that element, is typically non-linear over wide concentration ranges, due to interelement effects between the analyte element and other elements making up the specimen matrix. Although in many cases limiting the analyte concentration range may allow the use of linear calibration curves based on type-standardisation, it is usually more desirable to work with general purpose calibration schemes which are applicable to a variety of matrix types over wide concentration ranges.

The development of materials with optimum fatigue characteristics hinges on a better understanding of the fatigue mechanism ( i .e ., fatigue crack nucleation and propagation) under specific loading conditions. A correlation was established between the residual macroscopic stress level--as measured by x-ray diffraction analysis, the fatigue damage in the form of slip-band formation and intensification, and the fatigue life at various applied stress levels of pure iron and low-carbon steel.

Residual stresses were measured by an automated diffractometer technique (Fe 211 Kα reflection, Cr radiation) and computer calculation of both macroscopic (line shift) and microscopic (line broadening) stresses . Surface fatigue damage was observed by optical microscopy.

We have studied a series of laminated thin films by x-ray diffraction to correlate their structural and magnetic properties. Previous works have shown that the signal-to-noise characteristics of laminated magnetic films with non-magnetic interlayers can exceed that of single layer magnetic films. In the case where the magnetic layer is known to have low signal-to-noise performance, the signal has been observed to increase as the number of layers whereas the noise increases as the square root of the number of layers. This yields a net improvement of the signal-to-noise ratio, making the overall film more attractive as a magnetic recording medium. In this paper, we investigate films which are laminated layers of magnetic CoPtCr and non-magnetic Cr. The films were deposited with sputtering parameters that generally give low noise characteristics in single layer films. Up to four layers of CoPtCr films were made with Cr spacer layers of 2 nm. We observe some improvement in signal-to-noise characteristics and reduction in coercivity. X-ray diffraction analysis shows that the crystallographic c-axis, which corresponds to the magnetic easy axis, becomes more preferentially oriented perpendicular to the film plane with each additional layer. This change in preferred orientation is consistent with the reduced in-plane coercivity of the film. In the double CoPtCr layer with one Cr spacer layer experiment, we see that as the Cr spacer layer is increased from 0.5 to 8 nm, the c-axis of the CoPtCr again becomes more preferentially oriented out of the film plane, resulting in decreased in-plane coercivity. The media signal-to-noise improves once the Cr spacer layer is beyond 2 nm, consistent with previous observations.

We are engaged in a study of the ash produced by combustion of lignite in a 750-MW power station. The aim is to follow the transport of elements with Z> 16 from the mine, through: a) the combustion process, b) emissionto the atmosphere or c) deposition in a land fill, d) transport in the environment and e) subsequent uptake by animals and humans. The resulting data will be used to estimate potential adverse impact on human health caused by operation of the power station.

The Microemission X-ray Spectrograph is the result of the consolidation of the fine focus electron optics employed in the X-ray microscope, and the spectrograph goniometer used in fluorescent X-ray analysis.

The electron beam, 5 microns in diameter, directly bombards the sample under study. The beam is focused using a three element electrostatic lens system.

Provisions are made for continuous sample viewing with light optics. Sample manipulation, provides for complete coverage of a sample one-half inch in diameter.

The characteristic X-rays generated at the sample are allowed to pass through a beryllium window and fall on the analyzing crystal.

The curved crystal diffracts the characteristic X-ray wavelengths and refocuses them at the bilateral slit ahead of the detector. The goniometer may either be hand operated or motor driven through the various 2 θ angles. Electron beam currents are regulated by controlling filament power oscillator output. Signals are fed through a preamplifier into a rate me ter and recorder or into a high speed sealer which may be set to count for accurate preset periods of time. Samples may be investigated either by complete spectrum analysis of a single point on the sample or by determining concentration changes of a particular element by moving the sample across the electron beam.

Recent advances in MOS integrated circuit technology have opened new, high-volume applications utilizing epitaxial silicon-on- insulating substrates. To provide good quality heteroepitaxial silicon films for the semiconductor industry, a development program has been established to improve both the crystalline quality and the fabrication techniques for the most promising current substrate, magnesium aluminum spinel.

The role of X-ray diffraction techniques in the investigation of crystal quality, substrate surface quality, and epitaxial film quality are discussed, and results interpreted as the program is traced from crystal growth to epitaxial film analysis.

The results of the fourth year of observations on the effects of self-irradiation on the lattice of 238(80%)PuO2 confirm the predictions derived from previous observations. Namely, the lattice constant continues to decrease with time but at a slower rate indicating an approach to equilibrium. Very small reductions are also noted in the half-width of the diffraction lines.

The development of X-ray fluorescence analysis of light elements (e.g. O, C, B and Be) has been carried out for many applications. Recently, the revolutional expansion of semiconductor electronic and memory devices has roused the needs of analysis and identification of the surface and the single- and multi-layered film structure in devices, using the fundamental parameter method for the soft and ultrasoft X-ray region. From the view point of the extensive studies of soft and ultrasoft X-ray measurements.

During the course of catalytic experiments on bulk copper single crystals, several crystals were intentionally oxidized to form thick (6000 Å) Cu2O films on the copper substrates. These oxidized crystals were investigated by means of a high temperature chamber installed on a General Electric XRD-5 X-ray diffractometer. It was discovered subsequently that the lattice spacings of the Cu2O decreased upon heating and increased upon cooling. Bulk single crystals and polycrystals of copper were oxidized at 3 Torr of air for several hours. All of the oxidized crystals were examined with copper and chromium radiation and both showed similar results. Typical of the results was an oxidized (110) copper disc which showed a net contraction upon heating of 1% for the (110) Cu2O planes. This slightly oriented Cu2O film was distinguished because -it contracted on heating to 440°C from room temperature, then expanded from 440°-540°C, and then expanded again when cooled from 540°C to room temperature. CuO also was detected in the diffraction pattern and the CuO and copper spacings were behaving normally with the temperature changes. A polycrystal of Cu2O was'examined and that, of course, also acted normally as its temperature was varied. Borie and co-workers have reported and explained very nicely similar anomalous behavior for thinner (500 Å) (110) oriented Cu2O films grown on (110) copper substrates. They showed that the epitaxial forces would cause an oxide film grown at high temperatures to contract parallel to the metal interface and expand normal to the interface as the copper cools and contracts. The oxide would expand normal to the surface in. order to keep its unit cell volume constant.

It is felt that epitaxial forces are not causing the anomalous behavior in the present work mainly because the 6000 Å of Cu2O is too thick for epitaxy to exert a meaningful force. The oxide film on the (110) copper was slightly (110) oriented but all of the Cu2O reflections behaved similarly. An additional reason to discount epitaxy is that this Cu2O film expanded upon heating from 440°-540°C. For these thick oxide films epitaxial forces do not seem to be the controlling factor; therefore, a point defect mechanism must be the cause. Changing oxidation and diffusion rates with temperature would produce various vacancy concentrations in the oxide layer and cause the spacings to vary.

The mass absorption coefficient is a useful parameter for quantitative characterization of materials. If the chemical composition of a sample is known, the mass absorption coefficient can be calculated directly. However, the mass absorption coefficient must be determined empirically if the chemical composition is unknown. Traditional methods for determining the mass absorption coefficient involve measuring the transmission of monochromatic X-rays through a sample of known thickness and density. Reynolds (1963,1967), however, proposed a method for determining the mass absorption coefficient by measuring the Compton or inelastic X-ray scattering from a sample using Mo radiation on an X-ray fluorescence spectrometer (XRF). With the recent advances in solid-state detectors/electronics for use with conventional powder diffractometers, it is now possible to readily determine mass absorption coefficients during routine X-ray diffraction (XRD) analyses.

Using Cu Kα radiation and Reynolds’ method on a Siemens D-500 diffractometer fitted with a Kevex Si(Li) solid-state detector, we have measured the mass absorption coefficients of a suite of minerals and pure chemical compounds ranging in μ/ρ from graphite to Fe-metal (μ/ρ = 4.6-308 using Cu Kα radiation) to ±4.0% (lσ). The relationship between the known mass absorption coefficient and the inverse count rate is linear with a correlation coefficient of 0.997. Using mass absorption coefficients, phase abundances can be determined during quantitative XRD analysis without requiring the use of an internal standard, even when an amorphous component is present.

Measurements have been made on the FeLII/LIII intensity ratio on oxide free iron surface produced by evaporating a 50 Å Ti film on iron. These results show that the reported increase in the FeLII/LIII ratio with decreasing accelerating voltages is due largely to surface oxide and not self absorption. Also, for the vacuum presently used by soft x-ray spectroscopists the oxide surface on metals contribute strongly to the soft x-ray spectra of the bulk material for accelerating voltages below 4 kV.

The intensity of Compton scattering, Fe, and Ca chatacteristic radiation can be used to estimate the amount of ash in coal by Xray fluorescence spectroscopy. Mo, W, and Cr radiation were used to study a suite of New Mexico coals, and the best results were obtained with Mo and W X-ray tubes. If the actual concentrations of Fe2O3 and CaO and the mass absorption coefficient, μ*, at the Compton wavelength of scattered Mo K radiation can be determined, the regression equation:

%Ash - 24.2μ* - 6.28(%Fe2O3) - 1.96(%CaO) - 3.4

estimates the ash content with an average error of 0.5% ash at 0.71Å.