Table IV.
(16) Horrigan, V. &I., Fassel, V. A., Goetzinger, J. W., Zbid., 32, 787 (1960). (17) McDonald, R. S., Fagel, J. E., D.C. Ballis, E. W., Ibid., 27, 1632 (1955). carbon-arc, (18) McKinley, T. D., Pitt. Conf. on wt. % Anal. Chem. and Applied Spectroscopy, Vacuum fusion, oxygen Pittsburgh, Pa., March 1959. wt. oxygen Gas (19) McKinley, T. D. “Procedure for chromatoPt bath, Pt-Sn bath, Preparation of Absolute Oxygen Stand1700” C. graphic 1900” C. ard,]’private communication, 1959. 0.48 0.49 (20) Mallett, hl. W., Talanta 9, 133 0.45 0.31 0.31 0.31 (1962). 0.20 0.23 (21) hlilko, J. A., Adams, R. E., Harms, 0.20 0.14 0.13 W. O., in “The Metal Thorium,” Wil0.13 0.080 helm, H. A. ed., Chap. 13, American 0.079 0.083 Society for Metals, Cleveland, Ohio, 0.46 0.50 0.47 1958. 0.29 0.32 ... (22) Schutze, M. Ber. 77B, 484 (1944). 0.27 0.30 0.30 (23) Simmons, C. R., in “The Rare 0.25 0.26 0.23 Earths,” Spedding, F. H., and Daane, 0.12 0.13 0.11 A. H., ed., Chap. 18, Wiley, Kew York, 0.047 ... 1961. 0.047 (24) Sloman, H. A., Harvey, C. A., 0.039 0.040 ... Kubaschewski, O., J. Znst. Metals 0.038 0.036 ... 80, 391 (1951-52). (25) Smiley, W. G., Nucl. Sci. Abstr. 3, 391 (1949). (4) Booth, E., Bryant, F. J., Parker, A,, (26) Smiley, W. G., ANAL. CHEM.27, Analyst 82, 50 (1957). 1098 (1955). (5) Booth, E., Parker, A., Zbid., 83, 241 ( 2 7 ) Stanley, J. K., von Hoene, J., (1958). Weiner, G., Ibid., 23, 377 (1951). (6) Booth, E., Parker, A., Zbid., 84, 546 (28) Tucker, R. C., Gibson, E. D., Carl(1959). son, 0. N., Nucl. Metall. Series X, ( 7 ) Carlson, 0. N., Bare, D. W., Gibson, 315 (1964). E. D., Schmidt, F. A., in “Symposium (29) Turovtseva, Z. M.,Litvinova, N. F., on Newer Metals,” ASTN Spec. Tech. “Proceedings of the Second U. N. InterPubl. SO.272, pp. 144-159 (1959). national Conf. on Peaceful Uses of (8) Everett, &I. R., Thompson, G. E., Atomic Energy,” Vol. 28, pp. 593-603, Analyst 87, 515 (1962). United Xations, New York, 1958. (9) Fassel, T’. A., Dallmann, W. E., Winge, R. K., Fassel, V. A., ANAL. Skogerboe, R., Horrigan, T’. M., A N ~ L . (30) CHEM.37, 67 (1965). CHEM.34, 1364 (1962). (31) Wood, D. F., Oliver, J. A., Analyst (10) Fassel, I-. A., Goetzinger, J. W., 84, 436 (1959). Spectrochim. Acta 21, 289 (1965). (32) Yeaton, R. A., Vacuum 2, 115 (1952). (11) Fassel, T. A., Gordon, W. A., ANAL. CHEX.30, 179 (1958). (12) Guldner, W. G., Talanta8,191 (1961). (13) Guldner, W. G., Beach, A. L., AXAL.CHEW22, 366 (1950). RECEIVEDfor review October 29, 1965. (14) Hanin, &I., Rev. MBt. 57,1133 (1960). Accepted December 13, 1965. Con(15) Hansen, W. R., hlallett, hl. W., tribution No. 1822. Work performed in Trzeciak, hl. J., AXAL. CHEM. 31, the Ames Laboratory of the U. S. Atomic 1237 (1959)r Energy Commission.
Comparative Analytical Data on Determination of Oxygen in Yttrium
Absolute synthetic Carrier-gas fusion, wt. % oxygen standards, Pt flux, Pt-Sn bath, wt. 7 0 2100-2200’ C. 2300’ C. oxygen 0.46 0.48 0.48 0.29 0.32 0.31 0.18 0.20 0.20 0.11 0.13 0.13 0.069 0.081 0.080 Samples 1 0.4!3 0.50 2 0.30 0.32 3 0.27 0.32 4 0.22 0.25 n. 12 0.13 -.i 0.043 6 0.040 7 0.033 0.040 0.036 8 0.031 ~~
other metals, a t lower fusion temperatures than are required for a simple platinum bath. ACKNOWLEDGMENT
The authors are indebted to Royce
K. Winge and John W. Goetzinger for performing some of the analyses reported in Tables I11 and IV. LITERATURE CITED
(1) Albrecht, W. hl., hlallett, M. W., ANAL.CHEM.26,401 (1954). ( 2 ) Banks, C. T’,, O’Laughlin, J. W., Kamin. G. J.. Ibid.. 32. 1613 (1960). (31 I , Beach. A. ‘L.. duldner. JV’. G..’ in “Svmnosium on ‘Determination of Gases in “hI&als,” ASThl Spec. Tech. Publ. NO. 222, pp. 15-24 (1957).
Three-Wavelength X-Ray Absorption Edge Method for Determination of Plutonium in Nitrate Media E. A. HAKKILA, R. G. HURLEY, and G. R. WATERBURY University of California, 10s Alamos Scientific laboratory, 10s Alarnos, N.
b A new x-ray absorption edge method was developed for determining plutonium in nitrate solutions, In this method the transmitted x-ray intensities a t three wavelengths are measured. The KP x-ray for niobium and the K a x-rays for molybdenum and niobium are produced by irradiating a niobium-molybdenum secondary target with x-rays from a tungstentarget x-ray tube, and the intensities of these x-rays are measured after passing through an absorption cell filled successively with water and a solution of known plutonium content. Then the reduction in the transmitted intensities of the KP x-ray for niobium
M.
and the K a x-ray for molybdenum, which bracket the L 111 absorption edge for plutonium, are measured through the same cell filled with the sample solution. The absorption of these x-rays is related to plutonium concentration using accepted absorption principles. The method is applicable to the determination of plutonium concentrations of 10 to 25 mg. per ml. with a relative standard deviation of approximately O.6Y0.
A
method for determining plutonium in nitric acid solutions was needed to supplement potentiometric titration and radiochemical RAPID
methods for plutonium assay (3). The main requirements of the method were that it have a relative standard deviation no greater than 0.5% and produce results within 4 hours of receipt of sample. X-ray absorption edge methods, which provide the required speed and precision, have been applied to the determination of numerous elements, including plutonium ( 2 ), that have x-ray absorption edges in the 0.5- to 2-A. wavelength region. However, the conventional x-ray absorption edge method, in which measurements are made a t two wavelengths ( I ) , does not lend itself to reliable analysis of materials contaminated only with impurities that VOL. 38, NO. 3, MARCH 1966
425
Table 1.
Typical Data for Three-Wavelength X-Ray Absorption Edge Determination of Plutonium
Solution Water Standard (14.91 mg ./ml ,) Sample (0.8043 gram)
Parameter counts sec., corr. counts sec., corr. ratio (Io/I) log R counts sec corr. ratib (I~/I) log R
Wavelength where measured XZ (0.7107A.) Xa (0.7476A.) 512,000 1,024,000 1,024,000 49.90 28.70 30.20 512,000 1,024,000 1,024,000 213 0 71.9 86.3 4.269 2.505 2.858 0.63033 0.39881 0.45606 512,000 1,024,000 221.2 70.7 4.433 2.463 0.64670 0.39146
XI (0.6657 A.)
have low mass absorption coefficients. This can be shown by differentiation] with respect to R1, of the following equation for the concentration of the element being determined:
Table II. Precision of Three-Wavelength Absorption Edge Method for Determining Plutonium
Pu concn., mg./ml. 0
5.00 10.00 15.00 20.00 25.00
Std. dev., mg./ml. 0.040 0.070 0.064 0.091 0.134 0.120
Rel. std. dev.
...
1.4 0.64 0.61 0.67 0.48
Table 111. Three-Wavelength X-Ray Absorption Edge Determination of Plutonium in Nitrate Solutions
Pu found, mg./gram Po tentiometric X-Raya 191.3 191.9 228.6 229.1 216.5 215.5. 205.5 206.1 215.0 215.9 200.1 198.6 230.9 232.6 217.8 219.2 180.5 179.6 243 3 239.2 ~ .~ . . 206.6 207.0 248.7 250.9 210.3 211.2 209.8 210.6 231.9 235.9 197.7 196.4 149.9 150.6 156.5 158.1 155.1 155.2 154.7 154.8 155.7 157.6 151.0 150.6 151.1 151.1 156.0 155.1 155.5 155.7 182.5 182.6 176.3 175.5 Av . Rel. std. dev. a
Recovery,
% 100.3 100.2 99.5 99.7 99.6 100.8 99.3 99.4 100.5 98.3 100.2 99.1 99.6 99.6 98.3 99.3 100.5 101.0 99.9 99.9 98.8 100.3 100.0 99.4 99.9 99.9 100.4 99.8 0.67
Av. of duplicate detns.
426
ANALYTICAL CHEMISTRY
I
(water) errors in measurement of ki/k2 increase. The measurement of kl/kz may be performed indirectly by measuring the transmitted intensity through the standard solution containing the matrix impurity elements plus plutonium at a third wavelength, AS, selected so that an absorption edge for plutonium does not occur between Xz and AB. An equation analogous t o Equation 1, but with c = 0, can be written to relate measured intensity ratios at.% and X3:
k z / h = log Ra/log Rz = (Xs/Xz)"
(4)
If we assume that n does not change between X 3 and XI, Equations 3 and 4 can be combined to obtain: k,/k, where c is concentration in mg./ml., 11" is the intensity a t hl transmitted through the cell filled with water; I l is the intensity a t hi transmitted through the cell filled with the blank, standard, or sample; I z o and I z are corresponding intensities a t Xz; and kl and k0 are constants for a particular cell and impurity element system. For reagent blank solutions c = 0, and solution of the equation for kl/kz and differentiation with respect to R1 yields:
It is apparent from Equation 2 that as the mass absorption coefficients of the major matrix elements approach that of water, or as R1 approaches unity, log R1 approaches zero and errors in determining kl/kz become excessively large. Therefore, in absorption edge analysis of samples such as nitric acid solutions, it is difficult to obtain accurate measurements of kl/kz. For this reason, a new approach was developed for absorption edge analysis of nitric acid solutions for plutonium. THEORY
I n conventional two-wavelength xray absorption edge analysis, the values for kl and k z (Equation 1) are dependent on the absolute values of the two wavelengths used, the mass absorption coefficients of the impurity elements] and the path length of the cell (6). The ratio of the values can be expressed by the equation:
ki/kz = (Xz/XJn
(3)
where n represents the slope of the plot of log vs. log ( p / p ) for the matrix elements. Measurement of kl/kz by Equation 1 determines the value n. As the mass absorption coefficient of the matrix approaches that of the reference
=
(log R3/log
R2)log(Xz/Xl)/log(Xs/h2)
This expression and Equation 1 are utilized in calculating the concentration of plutonium in the unknown solution. The assumption that n does not change between X I (0.6657 A) and AB (0.7476 A) is not strictly valid because in determining kz/k3, plutonium is included as a matrix element and plutonium has an absorption edge (L I11 at 0.6863 A) between XI and Xz (0.7107 A,). The effect of plutonium on the value for kl/k2,as determined by the three-wavelength technique, is reflected in the consistently lower value of approximately 1.18 for kl/kz as compared to 1.24 measured for solutions containing only nitric acid. However, if the plutonium concentration of the sample is about equal to that of the standard, the error is insignificant. Although the calculations are more involved for this method than for the conventional (two-wavelength) absorption edge method, the analysis time is reduced because a reagent blank solution is not required. I n selection of the third wavelength, an x-ray line to the long wavelength side of an L 111 edge should be chosen. I n analyses where a K edge is used, the third wavelength may be to either side of the edge, and should be designated Xo if a t the short wavelength side of X i , with appropriate changes in derivation of Equations 4 and 5. EXPERIMENTAL
Instrumentation. A Philips Electronics Corp. inverted three-position x-ray spectrograph with a lithium fluoride analyzing crystal, scintillation detector, and Philips FA60 tungstentarget x-ray tube was modified for absorption edge analysis ( 1 ) . The x-ray tube was operated a t 50 kv. and 40 ma., and the multiplier phototube a t 680 volts. Polystyrene absorption cells of 1.0- and 1.5-cm. path lengths were fabricated for this study (1). A
niobium-molybdenum solid alloy, containing equal weights of the two metals, was inserted in the sample holder of the spectrograph and served as the secondary target. Reagents. *Analytical reagent grade chemicals and low conductivity water were used in all reagents. The plutonium standard solution was prepared using metal of 99.9801, purity which was prepared at Los Alamos by an electrorefining process (4). A 10.000-gram portion of the metal was dissolved by heating with 16N nitric acid and adding 2 2 5 hydrofluoric acid dropwise to maintain the reaction a t a reasonable rate. The resulting solution was diluted to 200.0 ml. with distilled water and nitric acid to provide a solution containing 50.00 mg. of plutonium per inl. in a final acidity of approximately 3 5 . Procedure. Accurately weighed or volumetrically measured aliquots of the nitrate solution (sample) containing 100 to 200 mg. of plutonium were transfeired t o calibrated 10.00ml. volumetric flasks, 4.0 ml. of 16N nitric acid were added t o each, and the solutions were diluted t o volume with distilled water. A plutonium solution containing 3.00 ml. (150.0 mg. of plutonium) of t h e standard plutonium solution and 4.0 ml. of 16N nitiic acid waq prepared in a final volume of 10.00 nil. in the same manner. The absoiption cell having a 1.00-cm. path length was filled with water, and the transmitted intensities of the Kp line for niobium (A]), the Ka line for molybdenum (A?), and the KO line for niobium (A,) were measured. A minimuin of 266,000 counts were accumulated a t each wavelength. The abiorption cell was next filled with the plutonium solutioii (150 nig. of plutonium) and tkx three intensity measurements mere r e p e a t ~ d . The cell was then filled successively with the other plutonium solution. (samples) and the measurements were made a t x1 and A?. -4t the conclusion of the analyses, the measurements for the water and known plutonium solution were repeated. A11 counting times were corrected for coincidence loss by sub-
tracting 4.0 seconds per each 106 counts accumulated. Typical data are shown in Table I. From the values for XI, Xz, and As, the exponent for Equation 5 is calculated to be 1.293. Using this value and measured values for log Rs and log Rz for the standard, k l / k z (Equation 5) is calculated t o be 1.190. Substituting measured values into Equation 1, one obtains 14.91 = (1.190) (0.63033)kz 0.39881 k2; or k z = 42.44 and kl = 50.50. The sample is then calculated to contain 16.05 mg. of plutonium per ml. in the 10.00-ml. volume, or 199.6 mg. of plutonium per gram of sample. RESULTS AND DISCUSSION
Precision. T h e relative standard deviations of t h e method were obtained by analyzing 6 N nitric acid solutions having known plutonium concentrations in the 0 to 25 mg. per ml. range (Table 11). The analyses were performed as discussed. Each value shown is calculated from duplicate measurements on each of seven samples. Effect of Nitric Acid. The effect of nitric acid concentration was investigated by analyzing 0.5 t o 11.2N nitric acid solutions containing 0 t o 20 mg. of plutonium per ml. Recovery of plutonium was determined using a solution containing 25 mg. of plutonium per ml. in 6N nitric acid as t h e known. Results indicate a significant deviation from 1007, in plutonium recoveries for solutions having low nitric acid concentrations and plutonium concentrations below 10 mg. per ml. The data show that the method is applicable to solutions containing 10 mg. per ml. or greater concentrations of plutonium in 2 to 1 l S nitric acid. Reliability. The method was applied t o t h e determination of plutonium in 27 nitrate solutions t h a t were analyzed previously by a wellestablished potentiometric method (3). -4s compared to the results obtained by
the potentiometric method (Table 111), the average of the plutonium found using the x-ray method was 99.801, with a relative standard deviation of 0.67. A statistically significant bias of the method was not indicated. The relative standard deviation was slightly higher than desired; however, the method is very rapid. One analyst can analyze approximately 15 samples in duplicate for plutonium per day, or a single sample in duplicate in 1 hour. Total operator time is reduced by 25y0 when calculations are performed by a computer. I n view of this rapidity of analysis, the small sacrifice in precision was considered acceptable. Although the method was developed specifically for analysis of samples having matrix elements of low mass absorption coefficient, it can be applied to any sample that can be analyzed by the conventional method, provided that the third wavelength is conveniently available. The main advantage would be that a blank solution is not required; the value for k l / k z can be obtained from either the standard or the sample solution. LITERATURE CITED
(1) Hakkila, E. A., Waterbury, G. R.,
“Developments in Applied Spectroscopy,” Vol. 2, p. 297, Plenum Press, hew York. 1963. ( 2 ) Hurley, R. G., Hakkila, E. A , , Waterbury, G. R., U . s. A t . Energy Comm. Rept. LA-3258 (1965). (3) bIeta, C. F., Waterburv. G. R.. “Treatise on Analytical Chemistry,” I. RI. Kolthoff, P. J. Elving, eds., Part 11, Vol. 9, p. 352, Interscience, New York, 1962. (4) Mullins, L. J., Leary, J. A , , U . 8. At. Energy Comm. Rept. LA-3118 (1964). ( 6 ) Peed, W. F., Uunn, H. W., Ibid., ORNL-1265 (1952). RECEIVED for review November 22, 1965. Accepted January 7, 1966. Work done under auspices of the Atomic Energy Commission.
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