This paper presents a review of the current status of photodiode array systems adapted for Energy Dispersive EXAFS (EDE) using a synchrotron radiation source. The performance of a conventional Reticon PDA is compared with that of a hybrid CCD. The specification of a new detector system for EDE is discussed in the light of experience gained with current linear detectors.

Existing Solid State Detector systems exhibit limitations in throughput rate and stability when used with intense synchrotron radiation sources. Recent work on a prototype detector system for Fluorescence EXAFS has allowed evaluation of new techniques, made possible by recent improvements in integrated circuit products. The knowledge gained from this investigation is enabling the design of high-count rate detector systems.

Historically, the development of XRF spectrometers has followed 2 main paths which are characterized by the means of spectral resolution they use. Those employing diffraction crystals and Braggs law to disperse the X-ray wavelengths are known as wavelength dispersive (WDX), whilst those usinq only the energy resolution of the detector, as enerqy dispersive (EDX). In the past these two have not normally been directly compared, because the WDX systems have always been the more expensive.

X-ray photoelectron spectrometry (XPS) has been a well established surface analytical technique for approximately 20 years. Fhotoelectrons are ejected by characteristic x-radiation. In our investigations we use Alκα-radiation. The depth from which l-l/e of the measured signal comes, is restricted to a few nanometers by inelastic mean free paths of photoelectrons in solids.

Proper sample preparation is very important for quantitative X-ray fluorescence analyses. Our first approach to fusing geological samples was a slight modification of a method described by Taggart(l) of fusing in platinum crucibles, with 1 g of sample to 10 g lithium tetraborate fired over bunsen burners. This method provided good results and was used until recently. Due to physical constraints, the required exhaust hoods could not be installed which prompted our investigation into new methods of fusion. The first reported application of a borate-glass fusion was in 1913(2); the melt consisted of 0.3 g of sample, 1.5 g of lithium carbonate, and 1.5 g of boron oxide (or about 3 g of lithium tetraborate). This mixture was heated in a graphite crucible at 1150 °C for twenty minutes and then poured into a brass ring on a copper-surfaced hot plate. Ironically our current procedure resembles this early technique.

X-ray micro fluorescence imaging refers to the use of an x-ray beam as a probe to excite XRF in a specimen and produce a spatially resolved image of the element distribution. The advantages of high sensitivity and low background, together with the nondestructive nature of the measurement, have lead to applications of x-ray microfluorescence analysis in biology, geology, materials science, as well as in the area of nondestructive evaluation. Previous reports have described the development of an x-ray microprobe which uses a conventional source of x-rays to produce a 10-μm beam. This paper describes improvements to the microprobe which have increased the beam power and the solid angle of detection. The data collection and display software have also been enhanced.

A non-contacting displacement measuring system utilizing focussed x-rays is being developed for use in hostile environments. Ultimately, this method will be used to measure mechnical strain under adverse conditions such as high temperatures, flame, cutting fluids, and gases with high velocity and pressure gradients. The foundation of the technique is the use of xrays, which are immune to the various environmental factors mentioned above. The proposed system uses a highly focussed, intense x-ray line which is scanned across markers that fluoresce secondary radiation. This secondary radiation level is then monitored using a photon detector and marker-focussed line overlap can be discerned. These targets can be used as fiducial markers demarcating a gage length, and the change in pointing angle of the focussed beam at target overlap is used as a measure of relative displacement. The present experimental systemcan consistently resolve 1.27 microns at ambient conditions, and 2.54 microns have been measured at a target temperature of 1900 de-grees F through an open flame. Given the performance of the current apparatus, equipment improvements should permit increases in resolution by a least a factor of 10 and measurements at much higher temperatures are possible.

X-ray fluorescence has a long tradition as an on-line analysis method in many kinds of industrial processes. It is capable of determining elemental concentrations in material flows even under severe and varying process conditions with an accuracy which is often sufficient for on-line control purposes. Many times the elemental concentrations correlate highly enough with those of the minerals of interest to give useful mineral analysis. In general, a rather well-defined geometry in the XRF measurement is necessary for accurate results, which may impose strict requirements on the sampling system.

In nuclear power plants the fast neutron fluence on the pressure vessel (PV) inner wall is measured by the scraping sampling method (1). As the inner plating of the pressure vessel contains 0.5 - 0.6 % of niobium, 93mNb (tt/2 = 16a) isomer is produced by the reaction 93Nb (n, n’). The activity of 93mNb is related to the fast neutron fluence.

Scraping samples (few hundred of mg) were taken from the PV inner wall. The niobium was chemically extracted from steel by using a HAP column. This extraction was needed to reduce matrix effects and to avoid interferences of other activities with 93mNb

Trace element determination by X-ray fluorescence spectrometry is subject, like almost all instrumental analytical techniques, to systematic errors, also known as matrix effects. This paper deals with the determination of mass absorption coefficients (MACs), using Compton peak intensities, for the correction of matrix effects arising only from elemental absorption in the sample.

When absorption effects are significant the relationship between net analyte peak intensity and concentration will no longer be constant, and corrections will be necessary for accurate analyses.

Undoubtedly the most important applications of X-ray fluorescence spectrometry (XRF) have been in the analysis of major elements where the technique provides a unique method of measuring the concentration of all elements having Z > 10 with extremely good precision in a wide range of matrices. However, XRF is in addition a powerful method for trace element analysis. In this discussion, the principles of the method for the trace element analysis of rocks are outlined, its capabilities are summarized, and the advantages and disadvantages of the technique are pointed out.

This paper describes the determination of the individual platinum-group elements by X-ray fluorescence after nickel-sulphide fire-assay collection. The platinum-group sulphide residue obtained after the dissolution of the nickel is dissolved in acid, and reduced to the metal by use of sodium borohydride. The finely divided metals are then filtered onto a millipore filter, and measured by X-ray fluorescence spectroscopy. The procedure makes use of gold as an internal standard. Factors affecting the accuracy and precision are investigated.

High-density brines are used to control high pressure during oil and gas well operations. These dense brines (15 to 20 lb/gal) are solutions prepared from sale such as calcium chloride, calcium bromide, zinc bromide and/or combinations. During stages of completion, excessive losses of these expensive brines to the production zone can occur. Before the brine is reused in other oil and/or gas well operations, the brine may need to be reweighted. An analysis of the brine composition must be obtained to properly add the correct amount of salts.

Standard addition or internal standardization methods are commonly used in X-ray fluorescence (XRF) applications but negate one of the advantages of XRF-elimination of tedious sample preparation. Scattered X-ray intensity has been used successfully to correct matrix effects in XRF applications. A Compton scatter ratio method is very advantageous for samples having a low atomic number, for which the scattered intensity is high. This paper describes an XRF method for determining Ca, CI, and Zn in high-density brines as well as the matrix correction for Br using a scattered X-ray ratio technique.

Environmental lead exposure continues to be a health hazard, especially to young children, and is a serious problem In the U.S. Since lead is stored in the skeleton, measurement of lead in bone (e.g. finger or tibia) can serve as an Indicator of lifetime exposure. Energy-dispersive x-ray fluorescence (XRF) currently seems to be the method of choice for non-Invasive testing, and is expected to be further developed for screening purposes.

Films of borophosphosilicate glass (BPSG) or phosphosilicate glass (PSG) are deposited on single crystal Si (100) wafers (typically 4 to 6 inches in diameter) by chemical vapor deposition processes during the fabrication of radiation-hardened microcircuits. These films act as insulator and as passivation layers. Since the P content of the glass layer is critical because of fluidity and corrosion problems, careful certification is required. The certification analysis has been accomplished here previously by empirical energy dispersive (ED) X-ray fluorescence (XRF) methods which use a set of expensive and fragile PSG wafer calibration standards. The results obtained were uncertain and the standards were sometimes broken.

Non-destructive analysis of Venezuelan pottery samples of different sizes and shapes from various archeological sites along the Orinoco River in the middle of Venezuela was performed by radioisotope X-ray fluorescence. The method employed a low intensity 109Cd source. The precision of the measurements for Fe, Rb, Sr and Zr from three different areas on each side of one of the artifacts was about 5%. A comparison of the data analysis using gross peak intensities and net peak intensities employing a digital filter technique to eliminate the background is presented. Finally an attempt to discriminate the samples of one location from another one or ones, assuming that the potter's clays were from different sources, is described.

Wavelength dispersive X-ray fluorescence spectrometry (WDXRF) is used for many types of routine analysis in the paper industry. Examples of routine elemental analysis include analysis of pigments in papers and coatings, analysis of fuels, and analysis of paper-mill waste. In the central analytical laboratory, however, WDXRF is frequently called upon in unique problem-solving situations. In some cases, these problem-solving applications later develop into routine methods.

In this paper, three examples of WDXRF being used as a problem-solving technique are discussed. These situations are: the determination of the cause of ring formation in lime-kilns, failure analysis of ceramic limekiln linings, and the determination of pigment distributions in alkaline papers.

With the ever increasing emphasis on computer-controlled hardware, computerized data processing and computer-based display of results, there is a tendency to forget the operating characteristics of some of the older, more mundane, components of X-ray diffractometers and X-ray fluorescence analysis units. We place our trust in the specifications of the components supplied by the equipment manufacturers and, while usually complete, it nevertheless behooves us to be well aware of the operation of the various hardware components of diffractometers and spectrometers.

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.

Many of the scientific programs proposed for implementation at existing and future synchrotron radiation sources involve measurement of the spatial distribution of transmitted or diffracted x-ray beams. The design of a general purpose position-sensitive detector for use in such experiments must address several conflicting requirements. Ideally, such a detector would meet the following criteria: high detection efficiency over a wide energy range, large dynamic range in measured photon intensities and response to a wide range of measurement intervals. Existing detector systems only partially meet these requirements, although much work has gone into improving the current technology.