We describe an adaptation of photon excited x-ray fluorescence analysis which is optimized for the analysis of small samples. A fine focus x-ray tube is used in conjunction with small diameter detector collimators in order to focus on a small sample volume with as high sensitivity as possible. Sample areas of less than 1 mm diameter can be analyzed with ppm detectability. In applications involving the analysis of human hair samples, a minimum detectable limit of 10 ppm Hg can be realized in a 1 mm long segment of a single hair in a counting time of 200 seconds. Simultaneous measurements of the sample mass can be obtained from the intensity of the incoherent scattering. An automated x-ray fluorescence analysis system using the technique for the scanning of elemental profiles in such hair samples will be described.

This paper presents an investigation on factors which contribute to the properties of the proportional counter system. The effect of the counter and the electronics has been discussed. A low noise detector preamplifier combination has been described. The resolution has been measured as a function of gas gain for the mixtures Ar-CH4, Ar-CO2, Ar-Xe and Ne-Ar. The gas gain ranges from 5 to 100. It has been found for all mixtures that the resolution of the detector improves slightly with lowering the gas gain. The recovery is most effective in Ne-Ar mixtures. The noise of electronics prevents the use of very low gas gains and for that reason determines the optimum gas gain regarding the resolution.

A distributed on-line analyzing system has been developed for automatic multielemental analysis of mineral slurries and solutions. The elements to be measured should be heavier than potassium. The system consists of measuring probes, a communication loop and a minicomputer with its peripherals. The measuring probe may either be directly immersed into the process stream or it is used with a sample cell in a by-line stream. Measuring probes are located at separate positions in the process. The measurement is based on X-ray fluorescence radiation which is excited with a sealed radioisotope source. The radiation is detected with a sealed high resolution proportional counter without filters. Spectrum stripping is based on reference samples which are measured in a computer controlled sequence in the same geometry as the sample. Thus possible instabilities in gain and resolution are under control. Chemical assays and slurry density are calculated from fluorescence and backscatter intensities. The minicomputer also controls the probes in the system and gives reports.

A Monte-Carlo model has been developed to calculate the effect entrance windows, or dead layers, have on the spectral shape and the counting efficiency of semiconductor detectors used in the low energy x-ray region (1 – 5 KeV).

Comparisons of energy- and wavelength-dispersive spectrometry inevitably focus on the count rate limitations of the ED electronics. In some cases the use of amplifiers without pulse pileup rejection, or worse, misadjusted pileup rejection circuits, has led to erroneous results and assumptions regarding maximum tolerable count rates which are far too low.

Proper evaluation of pileup rejection must consider both the count rate and energy dependence of the circuits. For example, using a typical ED spectrometer (EDAX, 154 eV, 10 mm2, 6 μsec amplifier time constant) we can first measure the total amplifier throughput curve as shown in Figure 1. This curve is only slightly dependent on photon energy, at least over the range from about 1-10 keV which usually contains the major part of the X rays, and shows a maximum stored count rate of slightly over 3000 cps for an input count rate of slightly less than 10,000 cps. Changing the amplifier shaping time constant will change the scale of the curve, but not its general shape.

Most integration of peaks in energy dispersive X-ray spectra is carried out using fixed energy “windows” or “regions of interest” set in terms of channels in the multi-channel analyzer (whether of the hardware or software based type). This gives rise to two sources of error that can be very significant hut can each be corrected with modest calculation effort.

Instrument specifications as published by manufacturers generally include values for stability of various parameters or components. For an X-ray fluorescence system, a typical example might be the generator high voltage stability (perhaps 0.01%). Parameters of this sort are of course of some use in comparing systems, and they may be (and often are) of great importance to the manufacturer as a criterion of manufacturing quality. It is difficult for the user to know how any single one, or combination of these factors really affect the total system performance as it may relate to his application.

Soft X-ray L-emission spectra of tin in second order diffraction and of niobium in first order have been studied in pure elements, in oxides, and in intermetallic Nb3Sn compound.

The study was done by a newly designed soft X-ray vacuum spectrograph. The curved crystal spectrograph is of the Johann type mounting. The radius of curvature of the bent crystal was 50.8 cm. The essential parts of the instrument are (i) an interchangeable bent crystal holder so that the spectrograph can cover a wide range of energy spectra by using crystals of different d-spacings to obtain highest resolution for the particular wavelength range; (ii) an adjustable Hartmann slit to control the effective width of the bent crystal; (iii) a half-shadow device to take two spectra onto the same film in the lower and upper half of the film; (iv) a sharp edge metal fixed to the Rowland circle to obtain a fiducial mark on the film; (v) a water-cooled rotatable Cu anode target; and (vi) a filament with both translational and rotational freedom to ensure optimum beam focusing.

The sensitivity of proton induced X-ray analysis (PIXE) as a multi-element, non-destructive technique has been exhaustively reviewed recently. This follows the pioneering work of Johansson et al. in this field, in which sensitivities of 10-12g were announced. Between the dates of these two references (1970 and 1976 respectively), numerous papers have been published on the use of this technique and on the optimization of experimental conditions (choice of incident particle and energy in particular). The wide range of analytical applications reported at the Lund conference showed conclusively that PIXE has established itself as a viable and powerful analytical method.

The use of particle-induced X-ray emission (PIXE) analysis as a standard analytical tool in the study of trace elements is well known. In the present investigation, an attempt is made to correlate human diseases with the presence or absence of trace elements and/or the changes in their concentration in healthy and diseased tissues. If such correlations do actually exist, trace element analysis could certainly be used as a diagnostic tool for the early detection of diseases and there is considerable interest in such information.

The former Deep Sea Drilling Project (DSDP) automated X-ray diffraction data collection and analysis system located at the Riverside campus of the University of California has been upgraded for use in the characterization of samples from natural hydrothermal systems by the addition of an interactive graphics terminal and the rewriting of the computer programs.

The system has the capability of collecting and interpreting patterns from 25-30 samples in one night's unattended operation. The computer's interpretation can be monitored and corrected easily. The pattern and the computed baseline are displayed with the peak locations and intensities, as predicted by the mineral standards file, and calculated mineral intensities superimposed. The system can display a pattern and accept and remember corrections to its interpretation in less than two minutes. The system can also organize and display the interpretations of a suite of samples in both tabular and graphical form.

The mineral identifications, minimum levels of detections and quantities calculated were tested using artificial mixtures of known composition and comparisons with other techniques and found to be adequate. As an example of the system's output, approximately 500 samples of cuttings from 12 boreholes drilled in the Salton Sea geothermal field in California have been run. The mineral modal analyses for samples from each well was produced in a diagrammatic format suitable for displaying on maps to show the three-dimensional distribution of mineral abundances.

The system gives adequate quality of analysis for the mapping of mineral abundances. The main benefit is the assumption of bookkeeping functions thus allowing the analyst to concentrate on the more difficult interpretation problems. The current drawback of the system is the difficulty in dealing with clays.

The analysis of mixtures of phases which produce complicated composite x-ray powder patterns is greatly facilitated by use of our profile fitting method and the technique of applying it is illustrated with a five-compound mixture. Profile fitting gave higher precision in the determination of the reflection angles and Intensities and resolved overlaps in a much shorter time than with other methods. If the reference standards are obtained with the same precision, a smaller error window width can b e used in the search/match procedure.

The inclusion of an internal calibrant in specimens prepared for Guinier-type focusing cameras is a well-established practice. The true reasons for performing calibration are, however, not always clearly understood. Accordingly, procedures adopted on the basis of this calibration for converting distances measured on the film into reliable values of θ vary in detail from one laboratory to another. The possibility that calibration curves can exhibit different degrees of reliability, depending upon camera alignment, is even less generally appreciated. The following account records efforts made over the years to come to terms with these problems in order to obtain unit cell dimensions at the 0.01 % level of precision from the routine measurement of Guinier diffraction patterns.

The method presented In 1976 for measuring stresses in polymeric materials including fiber-reinforced composites (1,2) yielded directly only one or two of the principal stresses and (elastic) strains in the embedded crystalline particles. The method is now extended so as to yield determinations of all three principal stresses σ1, σ2, σ3 and strains, ε1, ε2, ε3, The method applies to both residual and applied stresses and strains.

High angle diffractometry such as is used in ordinary X-ray stress determinations in metal objects is used, with suitable particles being embedded in a homogeneous plastic or reinforced composite before curing.

In X-ray diffraction and wavelength dispersive X-ray fluorescence, it is necessary to determine the intensity of a coherently diffracted X-ray peak with respect to its position, two-theta. To accomplish this, most X-ray diffractometers are provided with a scanning goniometer mounted X-ray detector that scans the angular two-theta region of interest and obtains X-ray Intensity as a function of time and therefore two-theta.