(1971). (283) C. Solomons, in "Techniques of Metals Research, Vol. IV, Part 2. Physicochemical Measurements in Metals Research," R . A. Rapp, Ed., Interscience, New York, N.Y., 1970, Chap. 6B, Sect. B, esp p 63. (284) H. Hoff, Electrochim. Acta, 16, 1059 (1971). (285) R. P. Van Duyne and C. N . Reilley, Anal. Chem.. 44. 142 11972). . , (286) lbid.. p 153. (287) lbid.. p 158. (288) J . Ruzicka and K. Rald, Anal. Chim. Acta. 53, 1 (1971). (289) E. Herczynska, Z. Phys. Chem. (Leipzig), 217, 139 (1961). (290) V. P. Maksimtchuk and I . L. Rosenfeld. Dokl. Phys. Chem.. 131, 253 (1960) (291) I . L. Rosenfeld and W. P. Maximtschuk, Z. Phys. Chem. (Leipzig), 215, 25 (1960). (292) N. Hackerman and R . A. Powers, J. Phys. Chem.. 57, 139 (1953). (293) S . P. Wolsky, P. M . Rodriguez, and W. Waring, J. Eiectrochem. Soc.. 103, 606 (1956). (294) N A . Balashova, V. V. Eletskii, and V. V Medyntsev, Sov. Electrochem., 1, 235 (1965). (295) W. W. Harvey, W. J. LaFleur, and H. C. Gatos, J. Electrochem. Soc.. 109, 155 (1962) (296) E. Herczynska and I. G. Campbell, Z. Phys. Chem. (Leipzig), 213, 241 (1960). (297) F. Jo1iot.J. C h m . Phys.. 27, 119 (1930). (298) K. Schwabe and W. Schwenke, Electrochim. Acta. 9, 1003 (1964). (299) K. Schwabe. ibid.. 6, 223 (1962). (300) K. Schwabe. Chem. Tech. (Beriin), 13, 275 (1961). (301) K. Schwabe, lsotopentechnik., 1, 175 (1960-1961) (302) K. Schwabe, K. Wagner, and Ch. Weissmantel, Z. Phys. Chem. (Leipzig), 206, 309 (1957). (303) K. E. Heusler and G. H. Cartledge, J . Electrochem. Soc.. 108, 732 (1961). (304) Z. A . lofa and V. G . Rodgdestvenskaya, Dokl. Akad. NaukSSSR, 91, 1159 (1953). (305) K: Schwabe, Z. Phys. Chem. (Leipzig), 226, 1, (1964) (306) J J Bordeaux and N Hackerman J Phys Chem 61, 1323 (1957)
(307) L. A . Medvedeva and Ya. M. Kolotyrkin. Zh. Fiz. Khim.. 31, 2668 (1957) (308) B. J. Bowles, Electrochim. Acta, 10, 717 (1965). (309) lbid.. p 731 (310) N . A. Balashova, V. E. Kazarinov, and G. N . Mansurov. Sov. Electrochem.. 6, 18 (1970). (311) K. Schwabe and Ch. Weissmantei, Z. Phys. Chem. (Leipzig). 215, 48 (1960). (312) F. Nagy, G. Horanyi, and J . Solt. Magy. Kem. Foly., 75, 530 (1969). (313) Yao Lu-an, V. E. Kazarinov, Yu. B. Vasiliev, and V. S . Bagotskii. Sov. Electrochem., 1, 146 (1965). (314) V. E. Kazarinov and N. A. Balashova, Dokl. Phys. Chem.. 134,911 (1960). (315) Y. Tot, Sov. Radiochem.. 5, 379 (1963). (316) G. P. Girina and V. E. Kazarinov, Sov. Eiectrochem.. 2, 776 (1966). (317) N . A. Balashova and G. G. Zhgmakin. Dokl. Phys. Chem.. 143, 217 (1962) (318) G. Horanyi, J . Solt, and F. Nagy, Magy. Kem. F o b . 75, 539 (1969) (319) J. Solt. G. Horanyi, and F. Nagy. ibid.. p 535. (320) A. N. Frumkin, G. N. Mansurov, V. E. Kazarinov. and N . A . Balashova, Coilect. Czech. Chem. Commun.. 31, 806 (1966) (321) N . A . Balashova. V. E. Kazarinov. and M . I . Kulezneva, Sov. Electrochem.. 6, 393 (1970). (322) V . E. Kazarinov, ibid., 2, 1070 (1966) (323) V. E, Kazarinov and G. N. Mansurov, ibid.. p 1223. (324) N . A. Balashova and V. E. Kazarinov. Russ. Chem. Rev.. 34, 730 (1965). (325) J . Richter and W. Lorenz, Z. Phys. Chem. (Leipzig). 217, 136 (1961). (326) N. A. Balashova and V. E. Kazarinov. Sov. Radiochem.. 7, 742 (1965) (327) N. A . Balashova, Doki. Akad. Nauk SSSR. 103,639 (1955) (328) E. Gileadi, L. Duic, and J . O'M. Bockris, Eiectrochim. Acta. 13. 1915 119681. (329) N A Balashova A M Kossaya and N T Gorokova Sov Electrochem 3, 583 (1967) (330) L A Medvedeva and Ya M Kolotyrkin Doki Phys Chem 143, 311 (1962) (331) C V King and B Levy J Phys Chem 60, 374 (1956)
(332) J . A. Kafalas and H. C. Gatos, Rev. Sci. Instrum., 29, 47 (1958). (333) R. Dreyer and I. Dreyer, Z. Phys. Chem. (Leipzig), 223, 423 (1963) (334) Jbid., D 283. (335) A. N . 'Frumkin, V. S. Bagotskii. 2 . A. lofa. and B. N. Kabanov, "Kinetics of Electrode Process," University Press, Moscow, 1952, p 53. (336) K. Hampartzumian and G. Raichevsky, in "Proceedings of the Third International Congress on Metallic Corrosion, Moscow 1966," Moscow, 1969, Vol. I l l , pp 421-7: distributor: Swets-Zeitlinger/Amsterdam. (337) A. V. Byalobzhesky, ibid., Vol. IV. pp 287-94. (338) K. H. Lieser and J . Ensling, Z. Phys. Chem. (Frankfurt), 67, 233 (1969). (339) N . A. Balashova, N. T. Gorokhova, and M. I . Kulezneva, Sov. Electrochem.. 4, 787 (1968). (340) T. Hurlen and G. Lunde, Electrochim. Acta. 8, 741 (1963). (341) R. D . Srivastava and H. Gesser, ibid.. 9, 1405 (1964). (342) G. M. Budov and V. V. Losev. Doki. Akad. Nauk SSSR, 122, 90 (1958) (343) D. M . Ziv, G. M. Sukhodolov, V. F. Fateev, and L. I . Lastochkin, Sov. Radiochem.. 8, 190 (1966). (344) V. Kuvik, Chem. Listy. 61, 149 (1967). (345) N. A . Balashova and V. E. Kazarinov, Sov. Electrochem., 1, 445 (1965). (346) K. E. Heusler and G. H. Cartledge. J. Electrochem. Soc.. 108, 732 (1961) (347) G. H. Cartledge and D. H. Spahrbier. ibid.. 110, 644 (1963). (348) G. H. Cartledge, ibid.. 113, 328 (1966). (349) G. H. Cartledge, in "Radioisotopes in the Physical Sciences and Industry," IAEA, Vienna, 1962, pp 549-57. (350) G. H. Cartledge, Corrosion. 11, 335t (1955). (351) / b i d . 15,469t (1959) (352) G H Cartledge. J Phys. Chem , 65, 1009 (19611 (353) G . - H.'Cartledge, Brit. Corros. J . . 1, 293 (1966). (354) J. O'M. Bockris. Ed., "E!ectrochemistry of Cleaner Environments, Plenum, New York. N.Y., 1972.
NOTES I
I
Rapid, Instrumental Neutron Activation Analysis for the Determination of Uranium in Environmental Matrices Jack
N. Weaver
Nuclear Services Laboratory, Nuclear Engineering Department, North Carolina State University, Raleigh, N.C. 27607
In the past few years, there have been many methods developed for the analysis of natural occurring uranium in a wide spectrum of materials. A recent article by Becker and LaFleur (1) discusses these and references the various techniques in a comparison of their method of NAA coupled with radiochemistry us. the other methods such as alpha counting, fission track counting, NAA, Amiel's (2) delayed neutron counting, etc. However, the point to be made is that although the Becker and LaFleur (and Amiel) methods are accurate and highly selective for uranium in trace quantities below 50 ppb, they still retain either the drawbacks of radiochemical procedures (when above 50 ppb) which require extra equipment, glassware, chemical manip(1) D. A. Becker and P. D. LaFleur, Anal. Chem., 44, 1508 (1972) (2) S. Amiel, Anal. Chem., 34, 1683 (1962).
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ulations in hoods, and a skilled chemist; or the handling of samples with significant gamma activity, the isolation and shielding of a nuclear reactor pneumatic terminal strictly for this use, and the use of a somewhat limited analytical system consisting of B'OF3 counters. As with all such techniques, the tendency is to use them sparingly only on important samples on a limited basis. The procedure described in this paper departs from these more detailed methods in that it represents a rapid instrumental method of neutron activation analysis for uranium in concentrations above 25 ppb, utilizing only a multichannel analyzer coupled to the Low Energy Photon Detector (LEPD). This procedure readily adapts to the typical scheme of a neutron activation analysis laboratory where irradiation, decay, and counting of the samples fit an efficient schedule, and it utilizes a detector (LEPD) which
A N A L Y T I C A L C H E M I S T R Y , VOL. 46, NO. 9 , A U G U S T 1974
has broad analytical capabilities other than uranium analysis (3, 4 ) . The LEPD detector operates on the principle that a wafer thin crystal of lithium drifted germanium is highly sensitive to the X-rays and low energy gammas from reactor irradiated materials, and it is basically insensitive to the usual interferences from higher energy gammas that are experienced with large volume Ge(Li) detectors typically used in neutron activation analysis. Considering the analysis of uranium by NAA, one of the fission products produced from the bombardment of 235U by thermal neutrons is 1331 with an 8% fission yield. This fission fragment has a half-life of 21 hours, and X-rays and low energy gammas a t 14.4, 18.32, 21.40, 100.08, 106.80, and 109.32 keV. The analysis of uranium in coal, bovine liver, orchard leaves, sea water, and various ores using the LEPD method is presented with significant improvements over other methods. These are: 1) No chemical dissolutions are required as is the case with many other techniques when applied to environmental samples. 2) Chemical separations which can give technique and recovery errors are unnecessary. 3) Either liquids or solids can be analyzed because of direct measurement of the X-rays emitted after irradiation in the reactor. 4) The analysis can be performed by a technician a t less expense rather than by a highly trained chemist.
URANIUM STAND A R0 _ ___ __
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Figure 1. X-Ray spectrum of 1331 (500 nanogram) standard after 4 hours of irradiation at l O I 3 n/cm2-sec., 48-hour decay, and a 400second count on a 16-mm ORTEC LEPD COAL OK -
v1
EXPERIMENTAL
w
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Apparatus. The apparatus used consisted of a 16 mm Ortec (LEPD) Low Energy Photon Detector and an ND2200 MCA coupled to a Hewlett-Packard computerized data retrieval system. This detector and its dewar are very similar in dimensions to a standard large volume Ge(Li) detector except in the actual construction of the germanium crystal itself. The windowless (less than 1 ym) lithium drifted germanium crystal wafer has a standard end cap window of a 5-mil thickness of beryllium. The detector is liquid nitrogen dewar cooled. The LEPD when coupled with a 1024 or greater multichannel analyzer has a useful range from 3 to approximately 600 keV. However, for practical purposes sensitivitywise, it is best below 300 keV. Typical resolution is 255 eV a t 5.9 keV, 600 eV a t 122 keV, and 750 eV a t 270 keV. Reagent Preparation. Weigh approximately 1 gram of freeze dried uranyl nitrate in 1 liter of distilled water and 0.1N nitric acid. Micropipetting is used to reduce standards to 0.1, 1.0, and 5.0 yg dried concentrations in poly irradiation vials. As a check on the uranium standards, three (0.10-gram) samples of an NBS Reference coal containing 1.35 ppm U were also heatsealed in poly vials and used as uranium standards. Procedure. After freeze drying, 0.25 gram of the solids (coals, liver, orchard leaves, etc.) were heat sealed in standard poly irradiation vials as per the uranium standards. Likewise liquids were transferred in 0.5-ml portions to poly vials for heat sealing. Both samples and standards, with flux monitors attached, were irradiated for 4 to 8 hours in a flux of 3 X l O I 3 n/cm2 sec. The irradiated samples were then allowed to decay for 48 hours before counting the 331activity. A decay of 40 to 50 hours provides the best decay time (especially for coals, ores, etc.) in a tradeoff of 13.31 decay us the background decay from other isotopes in the sample. As in a previous study ( 5 ) ,the solids are prepared in a special counting tray which provides a duplicate condition for both standard and unknown, while the liquids are simply transferred to clean standard poly vials for counting; since self-attenuation of the low energy photons in solids poses more problems than that with liquids. The standards were counted (decay monitored) on the 16-mm Ortec LEPD for approximately 400 seconds a t a calibration 0-125 keV. Figure 1 illustrates the spectra of 1331 from 236Ufissioning. All six photons are clearly defined but only four are abundant enough for quantitative analysis a t ppb levels. The photopeaks used were 14.4, 18.32, 106.80, and 109.32 keV. Hence, ratios between these photopeaks were used for ruling out interferences from other iso(3)J . N. Weaver, Amer. Lab., March, 1973. (4)M. H. Friedman, E. Miller, and J. T. Tanner, Anal. Chem., 46,236 (1974). (5) J. N. Weaver, Anal. Chem.. 45, 1950 (1973).
5
0 VI
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Figure 2. X-Ray spectrum of a coal sample after a 4-hour irradiation at 1013 n/cm2-sec., 48-hour decay, and a 400-second count on a
16-mm ORTEC LEPD topes present in the sample, thus providing a very accurate means of analysis. The coal samples were counted for 400 seconds while the bovine liver, orchard leaves, and sea water were counted for 1000 seconds because of a lower concentration of uranium in these SRM reference standards. Figure 2, an X-ray spectra of irradiated coal, clearly illustrates the fine resolution of the LEPD detector and the sensitivity with which it detects low energy photons. In the coal sample, only the 106.80-keV photopeak exhibited any interferences while the other three main peaks showed the correct half-life and internal ratios as the uranium standard. Data analysis was performed by the Covell (6) method and also by a computerized Hewlett-Packard, APT, and Nuclear Data ND2200 system.
RESULTS AND DISCUSSION
Listed in Table I are the results of the analyses of various environmental matrices for uranium. These range in substance from liquids (sea water) to solids (coals, bovine liver, and orchard leaves). An indication of the accuracy of the instrumental NAA-LEPD method is given in the comparison of SRM 1571 Orchard leaves a t very low ppb levels and with the NBS-EPA Round Robin Coal at ppm levels. Very good agreement is obtained at these levels. Because of the interest expressed in the trace element concentrations in fuels such as coals, Table I1 presents the uranium concentrations found in the U.S. Bureau of Mines (6)D. F. Covell, Anal. Chem., 31, 1785 (1959)
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Table I. Uranium Determination i n Environmental Matrices, ppm Sample No.
I N S . N A A , " LEPD
Other analytical techniques
Orchard Leaves, 0.032 f 0.009 0.026, 0.028 NBS SRM 1571 0.03 Beef Liver
