Over the last several years there has been growing interest directed toward high-resolution energy-dispersive x-ray detectors which operate at room temperature. The goal has been to develop a detector which combines the advantages of room-temperature operation characteristic of scintillation and proportional counters with the excellent energy resolution of silicon and germanium cryogenically cooled spectrometers. The elimination of the cryogenic coolant and the associated vacuum cryostat will permit the design and construction of really miniature and practically convenient x-ray detection systems which will find applications In already existing instruments as well as in various new fields.

Preliminary study of performance of an HPGe detector with an ion implanted entrance window in the spectrometry of the ultralowenergy x-rays is presented.

For the first time it has been shown that almost symmetric photopeaks and absence of low energy tailing can be obtained in this region from HPGe detectors.

Current developments in the recently introduced method of HgI2 crystal platelet growth by polymer assisted vapor transport are described. Crystal parameters are evaluated by making electrical measurements on x-ray detectors fabricated from HgI2 platelets, Selection for detector fabrication is on the basis of size and apparent crystalline perfection. Detectors have been fabricated with active areas averaging 2 to 3 mm2 and thicknesses ranging from 20 to 400 µm. Values of electron mobility and mobility-lifetime product measured for HgI2 platelet material are among the highest ever observed for HgI2.

The combination of low leakage current and good electron transport makes HgI2 platelets suitable for room-temperature x-ray spectrometry. An energy resolution of 370 eV (FWHM) for the 5.9 KeV Mn Kα line has been obtained, and representative low-energy x-ray fluorescence spectra are presented.

A review of the basic physical principles of the gas proportional scintillation counter is presented. Its performance is discussed and compared with that of other room-temperature detectors in regard to applications to portable instruments for energy-dispersive X-ray fluorescence analysis. It is concluded that the gas proportional scintillation counter is definitely superior to all other room-temperature detectors, except the mercuric iodide (HgI2) detector. For large areas or soft X-rays it is also superior to the HgI2 detector.

Two recent improvements in energy dispersive spectrometry are the development of time variant amplifiers and the introduction of pulsed X-ray sources. Either pulsed X-ray tubes or electron beams with fast beam blanking may be used.

Time variant amplifiers designed by Kandiah (1 ,2) used control logic to co-ordinate charge restoration of the detector preamplifier, pole-zero cancellation and baseline restoration. In the pulse shaping circuit, time constants are switched during the processing of each pulse to optimize throughput, baseline stability and pileup rejection. Pulse processing techniques have been discussed by Statham (3) .

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.

Our objectives in Instrument design & development are to improve the QUALITY OF THE DATA which can be obtained and presented to a computer system for analysis and to explore the corresponding choices which such improved data quality allows.

In usual EDXRF systems, the detector views the entire scattered and fluorescence radiation from a sample illuminated either by a direct beam or by a secondary target. In either case, the beam may be filtered before it strikes the specimen. Most efforts to mono-chromatize the exciting radiation or to reduce the background under the fluorescent peaks from the sample result in (a) decreases in X-ray flux available for excitation, (b) significant increases in power expended in the X-ray tube, or (c) extremely close coupling of the system components. These are NOT THE ONLY CHOICES AVAILABLE.

The use of polarized x-rays to excite fluorescence spectra with decreased backgrounds and improved detection limits is reaching a mature state of development. With bulk, low-Z specimens, polarized x-ray sources have produced detection limits which are ~℩ to 3 times lower than are obtained with the best unpolarized photon sources. Based upon experience and the known properties of larger solid angle geometries, further significant to dramatic improvements are anticipated.

The use of polarized x rays as the excitation source for x-ray fluorescence (XRF) measurements has been shown to significantly improve signal-to-background ratios. However, previous studies on polarized x rays applied to XRF techniques have concentrated on low-energy fluoresced x rays (<30 keV). In many cases strong matrix effects exist or the analyte is encased by a material that strongly attenuates low-energy x rays. These situations may preclude accurate assays based on L x-ray detection, and techniques based on the detection of higher energy K x rays may be more suitable because of the increased penetrability of higher energy x rays. The measurements and calculations reported in this work were made to assess the improvement in signal-to-background ratios and the increase in accuracy and detection sensitivity achievable by using polarized x rays as the excitation source for fluoresced x rays having energies between 25 and 110 keV.

Methods of correction for matrix differences are required in X-ray Fluorescence (XRF) Analysis when the overall composition of the unknowns is substantially different from the available standards. Sample preparation techniques used to minimize matrix differences often require development time and can consume irreplaceable sample material. Alternatively, the increasing computer power available to the analyst and the refinement of computer programs using fundamental parameter calculations has made this approach more attractive.

A system-consisting of a Siemens SRS-1 wavelength dispersive spectrometer (WDS), a KEVEX 0810-A/NS880 energy dispersive spectrometer (EDS), software for data collection and manipulation and a 40 element version of the NRLXRF fundamental-parameters analysis program has been put together to simplify XRF analysis of samples lacking standards of a similar composition. This configuration is shown schematically in Figure I.

Multichannel analyzers, as used in energy dispersive X-ray spectrometers using Si (Li), High Purity Ge, or other types of detectors, receive a series of pulses, generally in the 5 to 10 volt range full scale, which they measure and count in memory. Some are constructed using hardwired digital logic circuits to perform these memory control operations, while others incorporate standard computer memories and central processing units, with programmed logic for storing, displaying and (generally) processing the spectrum, with the advent of ever more powerful and lower cost microcomputers, it becomes increasingly attractive to adapt one to this purpose. We have done so, using an Apple II, and will describe the hardware of the interface, the logic of the data acquisition programs, and the utilization of memory in the computer.

The fusion technique for sample preparation for x-ray fluorescence analysis has been proven very successful for a wide variety of sample types. An inherent problem in the fusion technique has been the loss of sulfur during the fusion process. To extend our quantitative major element analysis method for geologic materials we have examined the problem of sulfur volatilization and have tested a variety of fluxes to determine their suitability to quantitatively retain sulfur during fusion, to produce a homogeneous glass disc that is suitable for presentation to an x-ray spectrometer with no additional sample preparation, and to help protect platinumware from attack by sulfide minerals.

Highly oxidizing conditions are necessary both to retain sulfur and to protect platinumware from sulfide attack. Previous researchers have shown that sulfur may be lost under reducing conditions. All of the fusions in this study were performed in an oxidizing environment, using a muffle furnace.

Since first introduced by Claisse, twenty-five years ago, borate fusions have been used in XRF analysis of a wide variety of materials because fusion eliminates many of the problems associated with particle size and matrix effects encountered in the analysis of powders. Geological and environmental materials such as rocks, ores, sediments, slags, air-borne particulates, etc., lend themselves nicely to lithium or sodium tetraborate or lithium metaborate fusion because the inherent presence of silica in these materials stabilizes the resultant glass from crystallization.

Elements of importance in a uranium-vanadium solvent extraction process can be monitored using EDXRF. Fifteen independent circuits were monitored for six different elements on a hourly basis. The precision of the analysis varies from element to element and from circuit to circuit, but all precision was within acceptable limits set for mill control by more conventional means of analysis. The elements of primary interest were uranium and vanadium.

The assessment of the environmental impact of mining and mineral processing is an important part of the research program of the U.S.D.I. Bureau of Mines. Under the Minerals Environmental Technology program, the Avondale Research Center evaluated the accessory minerals and elements, associated with the mining, beneficiation, and processing of phosphate rock in the central Florida phosphate district. In support of this project, a resinloaded paper (RLP) X-ray fluorescence (XRF) method was developed for determining uranium in these processing and waste materials.

Hydrogen peroxide is used to extract uranium by the in situ leaching of sandstone ore deposits containing uraninite (UO2). Since FeS2 minerals, marcasite and pyrite, also occur in these deposits and they consume hydrogen peroxide in their oxidation, it is important to determine their concentration.

A quantitative X-ray diffraction (XRD) method was therefore developed in order to monitor the concentration of marcasite and pyrite in sandstone ores.

The analysis of geological samples by x-ray fluorescence analysis is complicated by matrix effects and sample variability. Diluting the sample in a suitable matrix such as lithium tetraborate and then fusing it helps to reduce problems associated with sample inhomogeneities and reduces matrix effects considerably.

Unfortunately, many of the trace elements in the sample can be diluted below their detection limits by this technique. Pressing the ground powder into a hard disk avoids this problem and is less time consuming. Matrix effects can be very serious however, but can be calculated and compensated for by fundamental parameters programs.

Obsidian from eight localities in the San Francisco volcanic field of Northern Arizona was analyzed for 21 minor and trace elements (Ti, Mn, Fe, Co, Zn, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, W, Au, Hg, Th) usincf x-ray fluorescence analysis. All samples exhibited irregular analyzing surfaces. This was a more in-depth study of a previous study (1) in which a very small number of standards were used.

The data, in the form of intensity ratios relative to iron, were statistically analyzed and the trace and minor element patterns established. The obsidian clustered into four well-defined groups each consisting of two localities: Government Mountain/Obsidian Tank, Slate Mountain/Kendrick Peak, Robinson Crater/O'Leary Peak, and RS Hill/Spring Valley. The four distinct groups were treated individually to refine the separation between the similar sites. Classification function coefficients were calculated for each locality, then used to identify the source of thirteen obsidian artifacts recovered from a Northern Arizona archaeological site.