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The Washington Electron Probe Users' Group which consists of approximately 35 persons representing some twelve laboratories in the area was established in December, 1964. This group meets monthly for an informal exchange of information concerning current research practices and techniques. Instruments of three commercial firms, as well as laboratory constructed instruments, are represented. It became apparent to the group that there were problems of importance which could not be resolved through discussion alone. In order to clarify these problems, several systems of alloys and minerals were carefully selected for collective study and comparison. Wherever possible, these systems were chosen so that absorption, fluorescence, and atomic number factors could be individually evaluated. For example, in the iron-nickel system only an absorption conversion is required for nickel, while a relatively large fluorescence correction is necessary for the iron. In each of these tests, relative X-ray intensity data taken from instruments of the same manufacturer were compared in order to determine variations in the measurement process; in virtually all cases, agreement was excellent. Thus, it was deemed possible to evaluate conversion procedures for their relative merits. In cases where absorption is important, the major source of variability has been the X-ray mass absorption coefficient uncertainty rather than the conversion procedure. Also, when fluorescence corrections are required, the available conversion procedures seem to lead to results having approximately the same variability. The need for an atomic number conversion has been established, but the variability associated with the procedures postulated in the literature leads to greater uncertainty than the absorption or fluorescence conversion or both; this may be due to the fact that no completely acceptable theoretical basis for this conversion has yet been proposed. In all of this work, an interesting observation has been that addition of the concentrations to 100 per cent is not a suitable criterion for judging the correctness of either the measured data or the conversion procedure. As a result of the experience of the Washington Electron Probe Users' Group, advantages to individual laboratories from such group participation can and will be pointed out and suggestions given for the formation of electron probe users' groups in other sections of the country.
metallography, electron probes, interlaboratory tests, X-ray analysis, spectrochemical analysis
Birks, L. S.
Head, U.S. Naval Research Laboratory, Washington, D. C.
Gilfrich, J. V.
Research chemist, U.S. Naval Ordnance LaboratoryU.S. Naval Research Laboratory, Silver SpringWashington, MdD. C.
Metallurgist, National Bureau of Standards, Washington, D. C.