Complete Analysis of Uranium-Niobium-Zirconium Alloy by X-Ray Absorption Edge Technique J, H. Stewart, Jr., T. H. Barton, Jr., and M. R. Ferguson Nuclear Division, Union Carbide Corp., Oak Ridge, Tenn. 37830 The x-ray absorption edge techniqup has been extended to include the complete analysis of a U-Nb-Zr alloy. The alloy is dissolved in 6N HCI, HNOI and HF are added, and the U is determined. A rapid tri-nbutyl phosphate (TBP) extraction removes the bulk uranium. The Nb and Zr are then both determined in the aqueous phase. The intensity of the transmitted primary x-ray beam taken at wavelengths on each side of the three absorption edges is used to determine the concentrations of the three components. Twelve samples may be analyzed for the three components in an 8-hour period. The relative standard deviation of this method for the analysis of metal chips is 0.34% for U, 0.90% for Nb, and 2.2% for Zr.
CONTINUING INTEREST in alloying of uranium with one or more other metals has stimulated the investigation of new analytical techniques to replace classical colorimetric and gravimetric methods now used. The experimental work of Peed and Dunn (1) established the practical value of x-ray absorption edge spectrometry as a precise, accurate, analytical technique. Extensive preparation required for conventional analysis is not necessary, and matrix effects caused by varied concentrations of the constituent metals are absent (2). The method has been used (3, 4) for the determination of single elements in solutions and for the analysis of binary metal alloys. X-ray absorption edge spectrometry has now been extended to the complete analysis of a three-component metal alloy to utilize the inherent speed, accuracy, and economy of the method. If it is assumed that a sample consists of an element E, under analysis, and other impurities, it follows (5,6)that: I = Ioe-’[(PEcE)
+
(PSCS)
+
~.(PimpCirnp)l
(1)
where x is sample thickness; I, and I are the incident and emergent x-ray beam intensities; PE, ps, and pirnpare the mass absorption coefficients of element, solvent, and impurities; and CE, CE, and cimpare the respective concentrations. From the above relationship, a mathematical expression has been derived (1) relating the concentrations of the desired elements to x-ray intensity measurements taken at 20 angles (A, and XZ) on either side of the absorption edges. Concentration = KI log
(2)
where : (3) (1) W. F. Peed and H. W. Dunn, USAEC Rept. ORNL-1265, 1952. (2) R. E.Barieau, ANAL.CHEM., 29,348 (1957). (3) E. H.Liebhafsky, E. H. Winslow, and H. G. Pfeiffer, Ibid., 34,282R (1962). (4) W. J. Campbell and J. D. Brown, Ibid., 36,312R (1964). (5) A. H. Compton and S. K. Allison, “X-Rays in Theory and Experiment,” 2nd ed., Van Nostrand, New York, 1935,p. 513. (6) A.H.Compton, Ibid., p. 534.
and XIN
Kz = XPX,XZN
- XPX*XIN
(4)
This equation, in which t refers to the sample count time at A1 and at XZ corrected for counter resolving time and tw refers to the water count time corrected for counter resolving time at X1 and XZ, is utilized in the determination of the element in samples. The equation is valid whenever there is no absorption edge of an impurity element between X1 and Xz, the wavelengths on either side of the absorption edge of the element being measured. The values of N in Equations 3 and 4 refer to the atomic absorption coefficients at XI and at XZ, and the exponent has a value near 3 (6). The Kl and KZvalues are functions of the wavelengths XI and Xz and the absorption coefficient of the element at these wavelengths, and are not related to the element concentration. Thus, it is not possible to determine the K1, and KZvalues using only a single element in pure standard solutions. Two standard solutions, at least one of which contains added impurities, are counted at XI and XZ, and Kl and KZ values are obtained by solving the two absorption equations simultaneously. An average of several Kl and K2 values obtained from five or six standards containing uranium, niobium, and zirconium in the concentration range of interest is used. Of the possible uranium K, L, and M absorption edges, the L I absorp~ ~ tion edge was chosen since the absorption edge ratios are smaller for the LI and L11edges than for the LIIedge. The 116-keV x-rays required for the uranium K absorption edge were not available with the XRD-3 equipment, while the 16.3keV x-rays required for the LIIIedge were easily obtained. The K absorption edges of niobium and zirconium require only 19 keV and are used for the analysis. EXPERIMENTAL Equipment. The instrumentation consisted of the following components: General Electric Model XRD-3 x-ray spectrometer provided with a constant-potential filter and modified for monochromatic x-ray absorption as described by Barringer (7). The goniometer was fitted with the source and detector soller collimators and slits. General Electric Type CA-7 x-ray tube having a W target and operated at 30 kV (c.P.) and 9 mA. Lucite liquid-specimen cells mounted in a special cell holder on the source soller collimator. NaCl(lO0) analyzer crystal. Scintillation detector consisting of NaI :T1crystal and RCA Type 5819 multiplier phototube. Oak Ridge National Laboratories Model A1D preamplifier. Atomic Instruments Co. Model 218 linear amplifier. Berkeley Model 5426 preset counter. Berkeley Model 1556 timer, including Hewlett-Packard low frequency standard. Berkeley Model 1450 digital printer. In the modified spectrometer, the x-ray beam from the (7) R. E.Barringer, USAEC Rept. TID-7516 (Part l), 1956. VOL 40, NO. 1, JANUARY 1968
27
Table 1. Precision of Metal Chip and Standard Solution Analyses Std. solution analyses __ Metal chip-analyses . Rel. std. Rel. std. drv.. "
