It is of interest today to use polarized X-rays in X-ray secondary fluorescence as a means of improving signal to noise ratios in the analysis of trace elements. Current experimental design makes use of two mutually perpendicular scatterings from plane parallel materials. Radiation with the electric field vector in the scattering plane (scattering angle = 90°) will be annihilated. Hence, after the mutually orthogonal, 90° scatterings no source X-rays should reach the detector. In practice source X-rays will only be greatly reduced at the detector due to such things as multiple scatter and collimator divergence. An experimental problem associated with this design however is the reduced intensity of the signal because of the scatterings with concomitant increase in analysis time.

In the previous paper, ZRI, we have discussed the properties of single scatter radiation emanating from a point source, displaced a distance e° from the inside radius r* of a cylinder wall, scattering inside the wall, and reaching a point analyte on a diameter line with the source but removed a distance eA, from the inside radius. Figure 1 shows the instrumental design. It is to be recalled that a triangle inscribed by a circle with two of its verticles defining a diameter is always a right triangle. Thus all such scattering events described above are approximately 90°. This in turn almost annihilates the electric field vector in the scattering plane and creates essentially plane polarized X-rays at the analyte. If the analyte-detector line lies perpendicular to the plane of the cylinder, scattering of the polarized source X-rays by the analyte into the detector Is also a 90° event, and being perpendicular to the first scattering plane, should essentially annihilate the source X-rays at the detector.

The Refuse-Fired Steam Generating Facility (RFSGF) funded jointly by NASA, the U.S. Air Force, and the City of Hampton is presently in operation at the NASA/Langley Research Center in Hampton, Virginia. The facility b u m s approximately 200 tons/day of refuse and supplies approximately 170x103 tons/year of steam at 350 psig to the Langley Center. Concentrations of trace elements in the bottom ash and in the ash from the electrostatic precipitators were determined using the Murray State Polarized X-Ray Fluorescence Spectrometer (PXFS), The PXFS uses x-rays from a Phillips PW1140/96 x-ray generator in a double scattering process to make quantitative measurements on elements in pressed briquette samples. The double scattering process is used to produce polarized x-rays for excitation of the samples, Minimum detectable limits (MDL) of 1-3 ppm are achieved for elements with Z = 26 to 42. Lower Z elements have significantly higher MDL's; the lowest Z element detected, sulfur, has an MDL of 100 ppm. Elements with Z's higher than 42 have MDL's in the range of 4-10 ppm. Elements detected in the RFSGF ash were S, Cl, K, Ca, Ti, V, Mn, Fe, Cu, Zn, Br, Rb, Sr, Zr, Sn, Sb, and Pb. The concentrations ranged from a few ppm to several mg/g.

Energy dispensive X-ray spectrometry has been used extensively for the rapid, simultaneous deterninaion of elements in a variety of sample types. Excitation of the analytical sample can be by either X-ray tube, secondary targets, or radioactive isotopic sources. Tube sources have the advantages of convenient control of the excitation conditions, whereas an isotopic source or secondary target must be physically replaced by another to affect an excitation change. The use of primary filters between the sample and X-ray tube can greatly enhance the flexibilitty of the excitation conditions.

The detection limit of the proportional counter spectrometer is determined by the low-energy background caused by the wall effect. The choice of the filling gas of the proportional counter has been studied to minimize the background. Detection limits (3σ) for different elements have been calculated. Theoretical results have been compared with the experimental value obtained with Cd-109 and Am-24l excitation. The results are applied to the analysis of metal concentrations in oil samples and mapping the contents of zinc in the bark of living trees with a portable XRF-analyzer.

Spectrographic analysis for carbon and boron using fluorescent x-rays has been studied over the past few years; principles and applications for using those ultra-soft x-rays were described, based on the combination of total reflection and filtering rather than on the wavelength dispersive method of Bragg reflection (1, 2). However, oxygen and nitrogen, with x-ray wavelengths of 23.7lÅ and 31.60Å, respectively, cannot be detected as easily because of their high absorption by the detector window materials such as polypropylene, polyester or formvar films.

The ability rapidly and quantitatively to detect trace elements in a host matrix is of great importance in many areas of science and engineering. This fact is underlined by the considerable amount of effort that has been put into developing such techniques as electron probe microanalysis, proton Induced x-ray emission (Pixe), the laser microprobe mass analyser (Lamma) as well as conventional x-ray fluorescence methods. Recently the availability of electron storage rings partially or wholly dedicated to producing intense beams of synchrotron radiation has provided a new tpol to complement the above mentioned techniques. This paper reports on work at Daresbury Laboratory on synchrotron x-ray fluorescence (SXRF) fo r quantitative trace element analysis.

52 elements of the periodic system are considered as potentially usable by living organisms. Most of them, as some heavy metals, are required only in trace amounts. If a certain concentration of a given trace element is exceeded in an organism it becomes toxic. Plant analyses are considered in agronomy as a diagnostic tool and as a guide to fertilizer practice as the plant uptake is the best criterion of nutrient and micronutrient availability. But nowadays also toxic metals may be assimilated by plants due to the increasing contamination by inorganic compounds containing these toxic elements. In geosciences plant analyses may be of importance because indicator plants are employed for the geochemical prospection of certain heavy metals.