Over the past several years there has been considerable interest in computer search/match programs for qualitative analysis of powder diffraction patterns. This interest has been stimulated by the availability of modern minicomputers supported by relatively inexpensive mass storage devices capable of containing the entire JCPDS (l) data base on line. As the traditional search/match algorithms have been reviewed for possible implementation on the slower speed and restricted memory minicomputers being supplied with today's automated diffractometers, new ideas have emerged for such algorithms. One very extensive set of new algorithms has been developed by our group and these are contained in the SANDMAN search/match/identify program which was described at this conference last year (2). Experience has shown those algorithms to be extremely effective, particularly in handling eases where the presence of systematic errors in the data has precluded the correct analysis by other computerised search/match systems.

An IBM 7090 computer program has been written to determine precise lattice parameters for cubic, tetragonal, orthorhombic, and hexagonal systems. Leastsquares analysis is made with data fitted to the equation

where E is the eccentricity and A. is the absorption-divergence error. The computer program will make the least-squares analysis with neither, either, or both of the error(s) included. Data can then be reprocessed for other combinations of errors. After having determined the lattice parameter(s), on request, the computer program will predict the interplanar spacings, including the errors, so that observed data in the high-angle region may be indexed by comparison. Use of the program indicates that the most consistently reproducible parameters are obtained using only A, the absorption—divergence error.

A prototype of a new high temperature chamber has been developed at our institute. Like most of such chambers it has an evacuated housing which is watercooled, and in its center a tungsten heating strip is mounted on watercooled clamps (fig.1). A special way of clamping compensates for thermal expansion automatically and thus keeps the specimen in an aligned position. The specimen is mounted directly onto the heating strip's surface. Specimens are prepared using fine powders mixed with distilled water and acetone to give a thin slurry. This mixture is put onto the heating strip and carefully dried with a heatgun. This way of preparing a specimen makes it cling to the heating strip quite well even at temperatures above 3000K and therefore provides good thermal contact.

While x-ray fluorescence spectrometry is a highly sensitive and highly repoducible method of analysing samples, its one weakness is its relatively low sensitivity for light elements. This is mainly due to two problems: firstly the low fluorescent yield of the low atomic number elements, and secondly to the inherent inefficiency of exciting these elements. While it is not possible to improve the fluorescent yield, considerable improvements in light element sensitivity can be achieved by improvements in x-ray tubes.

Bremsstrahlung emission from four x-ray tubes operating at 12 to 300 kV was measured. Spectral distributions are given in terms of absolute-photon and energy fluxes. Silicon and germanium semiconductors, sodium iodide scintillators, and a xenon proportional counter were used to measure the spectra. Detector distortions were corrected by assuming an undistorted spectrum, distorting the spectrum with a Monte Carlo computer program, and comparing the results with measurement. The assumed undistorted spectrum was revised until the Monte Carlo calculation gave satisfactory agreement with spectral measurements from all four types of detectors. The effects on the spectra of varying the tube potential, tube current, target aperture, and detector aperture were investigated. Corrections for the intervening material and the solid angle subtended by the detector were applied to obtain the absolute-photon and energy flux from the target. Total fluxes in the L lines, K lines, and continuum are given. X-ray-production efficiencies varied from 0.026% at 12 kV to 1% at 300 kV. The constant of proportionality varied in the range (0.23 to 0.73) x 10-6 kV-1.

Improving the detection limits in TXRF by optimizing the excitation conditions is the goal of this work. The properties of the exciting radiation due to spectral distribution, polarisation, intensity and energy are investigated and compared to find best conditions. Results are given from experiments performed with synchrotron radiation, Bragg polarized monoenergetic x-rays, high energy cut-off reflector in the primary beam path of a high power x-ray tube and several geometries for the sample reflector.

X-ray tubes are used extensively in energy dispersive x-ray spectrometers in preference to radioactive sources because of their high output, variable intensity and tuneable energy spectrum. Tubes for this application have certain requirements which make them different in detail from the more common radiographic or therapy tubes and this paper sets out to present a review of some of the fundamental features of modern spectrometry grade tubes.

A low temperature attachment based on a miniature open-cycle Joule-Thomson refrigerator has been developed for x-ray diffractometry measurements over the temperature range from 65 - 400 K, By use of a special mounting plate, the device can be substituted for the heater assembly of a high temperature attachment and thereby utilize the available vacuum chamber and x-ray transparent beryllium window. The device is demonstrated by investigating the polymorphic phase transformations that occur in barium titanate.

Different diffraction patterns were compared one to the other in order to evaluate the contribution of different effects: Thus, in order to arrive at observing true differences between the patterns, “Diffraction Instrumental Monitoring” was adopted to assess reproducibility, stability, as well as differences in the instrumentation set up. To this end aberrations affecting peaks centroid position and variance were taken into account, Moreover the variation of variance of single peaks was analysed to achieve information on microcrystalline properties of real crystalline lattices.

The variations in the threshold registration of a number of plastic dielectric nuclear track detectors, DNTD's, have been investigated in terms of range energy relationships and the changes in structure affecting electron density distributions studied, using small angle X-ray diffraction. A similar mechanism has been employed to investigate the presence and formation of microcrystallite nucleation sites in lunar and terrestrial minerals, following proton and charged particle bombardments of 10-18 particles/cm2.

Clay minerals are one of the most difficult classes of materials to analyze by x-ray powder diffraction, yet powder diffraction is the only technique which can yield the important crystallographic information necessary to identify and classify the minerals. The importance of clay minerals in industry and in the studies of rocks, due to their chemical properties and sensitivity to geological changes, often requires the analyses of large numbers of samples in short periods of time. Such sample throughput requires computerized analysis* Because definitive, meaningful d-I data are difficult to obtain from the broad diffraction peaks obtained from most clay samples, this problem has been approached by using the whole diffraction, trace as the basis of a computerized analytical scheme.

A wavelength dispersive spectrometer which consists of a flat crystal analyser and a position sensitive proportional counter has been developed for X-ray fluorescence analysis using synchrotron radiation. The advantages of this spectrometer are high energy resolution, multielemental nature, and high efficiency, and these match well "with the high brightness synchrotron X-ray source. The minimum detection limits are of the order of ppm or pg. An application to elemental mapping has also been demonstrated. The present system is useful for practical analysis of small samples or small regions.

A low-temperature X-ray diffraction apparatus has been constructed to study structure and structural changes of electrolytes in the frozen state. This apparatus, which is inexpensive and easy to construct, is an attachment to a standard wide-angle diffractometer. Diffraction patterns may be obtained of various types of materials at any temperature from room temperature to −196°C with a control of ±1°C. The diffraction patterns are recorded on a strip-chart recorder as they are being obtained. Thus, this diffractometer method has several advantages over the camera methods usually employed for low-temperature X-ray diffraction work. A unique sample-introduction method is described which ensures a polycrystalline material suitable for obtaining diffraction patterns. Such patterns are shown for various concentrations of salts in water at several low temperatures, phase transformations being in evidence.

Escape peaks occur when the incident X-ray quantum, energy exceeds the absorption edge energy of the detector element and the resulting X-ray fluorescence is lost from the detector. The most common escape peaks result from 1 K-fluorescence in NaI-scintillation counters and Xe K-, Xe L-, and Kr K-fluorescence in proportional counters. The average pulse amplitude of the escape peak is proportional to the difference of the Energies of the incident and fluorescent X-rays. If the intensity of the escape peak is high as in the case of Mo Kα and a kryptoopreportional counter, and the lower level of the pulse height analyzer is raised to reject the escape peak, the quantum counting efficiency may be reduced by a factor of two. When the pulse height analyzer is set for characteristic incident radiation, escape peaks appear in powder patterns at small diffraction angles. These broad low-intensity peaks are often mistakenly identified as resulting from misalignment, scattering, etc. Each powder reflection can produce its own escape peak which occurs at an angle slightly smaller than the absorption edge of the detector element. In a silicon powder pattern the three strongest reflections produce three resolved escape peaks whose peak intensities are about 4% of their corresponding Cu Kα peaks when the X-ray tube is operated at 50 kV. The escape peak intensities decrease with decreasing X-ray tube voltage and disappear when the voltage is lower than the absorption edge energy of the detector element. Absorption edge peaks observed without the upper level of the pulse height analyzer are similar in appearance, intensity, and diffraction angle to the escape peaks. In complex powder patterns the escape peak pattern is unresolved and may produce a number of very broad peaks.

When an x-ray diffraction profile Is measured for stress analysis or profile analysis by the use of a linear (straight line) position sensitive proportional counter (PSPC) , a convex-type background line is obtained because of the geometrical problem and the absorption of x-rays. Such phenomenon is remarkable when a wide angular range is set on a linear PSPC and it is, in particular, necessary to correct with a straight background for accurate measurement of diffraction angle or half-value breadth of the broadened diffraction profile.

Applications to nonmetallic specimens such as minerals will be shown and the special techniques required for such specimens described. These include coating the surface with a thin conducting layer and prepho to graphing to map out the areas of interest. Specific examples of copper-iron minerals will be given. Other applications to metallic systems such as mass transfer studies in liquid metal cooling systems will also be shown.

The P-L2,3 emission spectra of the phosphorus compounds were obtained using a secondary excitation. We found that the spectra depended upon the chemical state, the main peak of L2,3 emission spectra shifts to a higher energy, and the peak of intensity of higher energy increases with an increase of oxidation number. It should be noted that the phosphorous spectra of the phosphate anions scarcely reveal influences of the phosphate compounds, except that of H3PO4. We concluded that the spectral feature for the phosphorus compounds is influenced by the condition of surrounding atoms but is not influenced by the bond condition.

This paper reports and discusses the results of a computer modeling study on powder diffraction profile analysis for crystallite size and strain of polycrystalline materials. The results of this computer modeling show that if the spans of diffraction profiles in reciprocal space (1/d) are not carefully chosen, an overestimation on size and an underestimation on strain may result in analysis by both the Warren-Averbach and the Hall-Williamson methods. A general way to eliminate such errors based on profile fitting and regeneration is presented and discussed in this paper.

Increasing attention is currently focused on the generation of characteristic x-ray by proton irradiation. This has the advantage of yielding “clean” x-ray- i. e. free from background brerasstrahlung radiation, from even the lightest elements. The disadvantage is that the yields are naturally much lower than those produced by electrons of the same energy. A recent study has extended characteristic x-ray production to a variety of heavy ions and has shown that the cross- sections for the production of clean x-rays are often higher , by as much as several orders of magnitude, than those produced by protons of the same energy. In addition, there has emerged a further advantage, viz. the ability of specially chosen heavy ions to excite characteristic x-ray from a particular element in a selective manner. Since heavy ions penetrate only a few hundred Angstroms in to most solids, the phenomenon can be used as the basis of a technique for the examination of surface deposits, or to measure depth distributions of impurities. For example, Kr ions can be used t o determine the range distribution of antimony which had been implanted in to silicon at 100 keV. The antimony concentration was determined as a function of ∼ 150 Å steps, and was found to exhibit a maximum concentration of ∼ 1 part in 103 of silicon at 450 Å below the surface, falling to zero concentration at ∼2000 Å a depth. In the past, in order to obtain the required degree of sensitivity, such range determinations have relied on radio active tracer techniques.

An entirely new type of proportional counter has been developed during the course of these studies. This instrument, because of its special construction, can be positioned very close to targets in non-dispersive studies, so as to collect the highest possible fraction of emitted x-ray. It incorporates a replaceable anode unit, together with a built- in miniature head amplifier, and exhibits extremely good performance, particularly for ultra-soft x-ray. In addition, rotation of a dial on the end of the counter body allows alteration of the active gas volume during operation, and so permits tuning into x-rays of a particular energy.

A model is under development at this laboratory to predict the mobilization of Th from an estimated 20,000 metric ton deposit, in place and weathering as long as 80 million years on the Morro do Ferro, a hill on the Pacos de Caldas plateau in Minas Gerais, Brazil. The significance of this deposit lies in the marked similarities, chemically, between Th and Pu with reference to the problem of Pu waste management from the nuclear fuel cycle. One of the objectives of this program is to determine the elemental composition of the Morro do Ferro soil and its relationship to the mobilization of Th from the deposit. X-ray fluorescence is used for the analysis of Th, U, Ba, La, Ce, Pr, Nd, Sm, Dy, Eu, Gd, Yb, Hf , Fe, Zr, N b , Mo and Pb. This paper describes the XRF system and methodology used for the determinations and presents the results of 72 core, soil and sediment sample analyses for the above 18 elements. Analyses of three United States Geological Survey (USGS) rock standards are also presented.