Robert D. Giauque

X-ray microprobe using multilayer mirrors

Abstract Multilayer reflectors for the X-ray region have now progressed beyond the experimental stage to the point where they can be relied upon as optics for experimental systems, in synchrotron radiation research as well as in other fields. This paper reviews the design considerations for an X-ray microprobe, and summarizes experience with prototypes tested at both SSRL and NSLS. The optical systems described employ multilayer-coated spherical mirrors arranged in the Kirkpatrick-Baez configuration to demagnify the X-ray source by a factor of several hundred. By this means a spot of X-rays less than 10 μm square can be produced. The optical aberrations and other factors that limit the performance are detailed, and possible ways to improve the performance are discussed. In the prototypes the spot is directed on the specimen which is carried on a stage that can be translated horizontally and vertically. The characteristic fluorescent X-rays excited by the focused 10 keV photons are analysed by an energy-dispersive Si(Li) detector, so that by scanning the stage an elemental concentration map of the specimen is built up. In a companion paper [A.C. Thompson, J.H. Underwood, Y. Wu, R.D. Giauque, K.W. Jones and M.L. Rivers, these Proceedings, p. 318] some experimental programs are described, and estimates of the elemental sensitivity are provided.

RAPID QUANTITATIVE ANALYSIS BY X-RAY SPECTROMETRY

An x-ray fluorescence analysis method applicable to the case of fluorescent spectra excited with monoenergetic x-rays has been developed. The technique employs a minimum number of calibration steps using single element thin film standards and depends upon theoretical cross sections and fluorescent yield data to interpolate from element to element. The samples are treated as thin films and corrections for absorption effects are easily determined. Enhancement effects, if not negligible, are minimized by sample dilution techniques or by selective excitation.

Biological trace-element measurements using synchrotron radiation

The feasibility of performing X-ray fluorescence trace-element determinations at concentrations substantially below the ppm level for biological materials is demonstrated. Conditions for achieving optimum sensitivity were ascertained. Results achieved for five standard reference materials were, in most cases, in excellent agreement with listed values.Minimum detectable limits of 20 ppb were measured for most elements.

X-ray induced x-ray fluorescence analysis of suspended air particulate matter

This .report reviews critical aspects of x-ray induced x-ray fluorescence analysis that should be considered for quantitative elemental analysis of suspended air particulate matter. Included are considerations which influence sensitivity and precision in x-ray fluorescence analysis using semiconductor detector spectrometers. The analytical capabilities of spectrometers employed during these studies will be illustrated. Also, a method employed to compensate for particle size effects when analyzing for lower atomic number elements is discussed. ... This report was prepared as partial fulfillment of an agreement with the Rockwell International Science Center, Thousand Oaks, Calif., to participate in Phase II of. the California Aerosol Characterization Experiment during 19731974. This program was sponsored by the California Air Resources Board. In addition to .this report, approximately 550 time related aerosol specimens were analyzed by x-ray fluorescence. The program manager has been supported in analysis and interpretation of the data obtaihed during the study. Work performed under the auspices of the u. s. Atomic Energy Commission.