indium-115m could not have been produced by nuclear reactions on other elements. ACKNOWLEDGMENT
The authors express appreciation t o R. K.Durham for his helpful advice during the course of this investigation, and one of the authors to the International Atomic Energy Agency, Atomic Energy of Canada Ltd., and the Comisi6n Nacional de Energia At6mica (Argentina) for a postdoctorate fellowship. LITERATURE CITED
(1) Gaittet, J., Albert, P., Compt. rend. 247, 1861-3 (1958). (2) Goulding, F. S., Atomic Energy Can.
Ltd., Rept. AECL-431 [IRE Convention Record 4, 76-81 (1956)l. (3) Hawkings, R. C., Edwards, W. J., Zbid., Rept. AECL-819, 1-32 (1958). (4) Heath, R . L., U. S. Atomic Energy Comm., Rept. IDO-I6408,1-195 (1957). (5) Jenkins, E. N., Smales, A. A,, Quart. Revs. (London) 10, 83-107 (1956). (6) JerviR, R. E., Atomic Energy Canada Ltd., Rept. CRDC-730, 1-47 (1957). (7) Jervis, R . E., Mackintosh, W. D., Proc. Second Intern. Conf. Peaceful Uses Atomic Energy, Geneva 28, 470-7, paper 189 (1958). (8) Karabash, A. G., Peizulaev, Sh. I., Sl-yusareva, R. L., Rleshkova, V. M., Zhur. Anal. Khim. 14, 598 (1959). (9) Leddicotte, G. W.,Mullins, TV. T., Bate, L. C., Emery, J. F., Druschel, R. E., Brooksbank, W. A., Jr., Proc. Second Intern. Conf. Peaceful Uses Atomic Enerav, Geneva 28, 478-85. paper 927 ( i 9 G j . (10) Rleinke, W. W., ASAL. CHEX. 28,
736-56 (1956); Ibid., 30, 686-728 (1958); Ibid., 32, 104R-136R (1960). (11) Nat. Research Council, Natl. A d . Sci. ( U . 8.) Nuclear Data Sheets, NRC 58-9-66 (1958). (12) Plumb, R . C., Lewis, J. E., Nucleonics 13, No. 8, 42-6 (1955). (13) Stewart, J. C., Zweifel, P. I?. Proc. Second Intern. Conf. Peacefui Uses Atomic Energy, Geneva 16, 650-62, paper 631 (1958). (14) Trapp, E. C., Proc. Sixth Hot Laboratories and Equipment Conference, Chicago, Ill., 1958, 306-11. (15) Yakovlev, Y. V., Kulak, A. I., Ryabukhin, V. A., Rytchkov, R. S., Proc. Second Intern. Conf. Peaceful Uses atomic Energy, Geneva 28, 496505, paper 2023 (1958). RECEIVED for review September 6, 1960. Accepted November 17, 1960. 4th Conf. on Anal. Chem. in Nuclear Reactor Technology, Gatlinburg, Tenn., October 12-14, 1960.
Separation of Radioactive Zinc from Reactor Cooling Water by an Isotope Exchange Method W. 8. SILKER Hanford Atomic Products Operation, General Electric Co., Richland, Wash.
b A method was developed to separate radioactive zinc from reactor cooling water b y isotope exchange with inert zinc in the form of zinc amalgam. The radioactive zinc is recovered in high yield and free from all other activities except C d 4 and traces of Md6 b y a single contact with zinc amalgam. The C d 4 interference can b e removed quantitatively b y a pre-extraction into cadmium amalgam. The procedure is rapid, and simple enough to warrant application to an automatic analyzer for continuous measurement of radioactive zinc in waste streams.
T
HE
HAKFORD PRODUCTION REACTORS
use treated Columbia River water to remove the heat formed by the fiqsioii proceqq. I n the reactor, the impurities in the n-ater are exposed to a high neutron flux, where a fraction absorb neutrons and become radioactive. These radioactive materials are discharged nith the water to retention basins where the short-lived radioisotopes are allowed t o decay. The water from these basins is then returned to the river. d long-lived radioisotope introduced to the rii-er in this manner is Zn", which is useful as a tracer in the study of biological systems that are dependent on the Columbia Rirer. Perkins and Nielsen measured the Zn65 concentrations in farm produce and livestock from land m-hich was irrigated n i t h Columbia River water, and measured the resultant
accumulation of individuals I\ ho obtained their food from these sources (4). Certain marine organisms in the Columbia River estuary achieve a high concentration factor for zinc; oybterP, for example, concentrate ZnG5by a factor of about 2 X 106 from their mvironment ( I . 5 ) . The interpretation of data from these studies requires a n accurate measurement of the amount of radioactive zinc continually discharged t o the river. Zinc-65 in reactor cooling water is currently determined by gamma spectrometric analysis of a n evaporated sample m-hich is allowed to decay for more than 5 days. If a n a n a l p i s is required prior to thia time foi or for Zn6gm,a short-lived isotope, a more complicated chemical separation iq required t o obtain radiochcmically pure isotopes of zinc. The possibilitiey for a iimple one-step procedure that could be adapted for automatic anal! were investigated. The radioisotopes in reactor cooling water that are present in amounts that n-ould interfere n i t h a y-spectral analysis. for Zn65 are KaZ4, As76, BaI40, and several of the rare earth isotopes. Copper-64, in addition to the previously mentioned isotopes, n ould interfere v-ith the measurement of the gamma photons from b e g r n , and euclusion of theqe i-otopes from the final product is required. Preliminary studies by DeVoe ( 2 ) suggested that isotope exchange on amalgams might find application in radiochemical analyqis n-here a high
decontamination factor is required. This paper presents a procedure using zinc ainalgani exchange to separate radioactive zinc from a complex mixture of other radioactive isotopes. This procedure can be used for the automatic determination of Zn65in waste streams, and is. suitable for routine determination of radioactive zinc isotopes by laboratory perronnel. EXPERIMENTAL
The zinc amalgam used in this work was prepared by the method of Morse and Burton (S), in which granular zinc and mercury in the ratio of 1 gram to 5 ml. were mixed in the presence of 0.1X tartaric acid. Simultaneous amalgamation and isotope exchange were equally effective in recovering radioactis-e zinc; consequently the use of 0.1X t,artaric acid 11-as adopted as the electrolyte for this procedure. A reasonable aliquot of reactor cooling water that could be used for the radiochrniical determination of Zn85 was 100 ml. T o determine the optimum amount of zinc amalgam for iise with this volume of samplt~,100 nil. of 0.1N tartaric acid was spiked nith Zn65 tracer and shaken for 5 minutes with various amounts of amalgam. The tn-o phases were separated and the amounts of radiozinc in each phase measured by conventional y-ray spec,trometric methods. The results, presented in Table I, indicate that 6 ml. of amalgam \\-w the minimum quantity to be used. Since the removal reaction is baaed on the interchange of atoms betn-em the VOL. 33, NO. 2, FEBRUARY 1961
233
solution and the amalgam t o a n equilibrium value, the degree of completion is time dependent. The reaction rate is at least partially diffusion controlled, and is dependent on the relative amounts of solution and amalgam as well as the degree of mixing. A time study under the conditions selected for this separation (6 ml. of amalgam, 100 ml. of sample, and mixing iTith a mechanical wrist shaker) indicated a n exponential rate reaction with a half time of about 1 minute. A contact time of 8 minutes was selected, which was long enough to ensure greater than 99% of equilibrium.
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Table I. Effect of Amount of Zinc Amalgam on Zn65 Distribution
Zinc -4malCounts per Minute gam, Aqueous Amalgam yoin MI. phase phase amalgam 2559 90.2 2 275 4 225 2495 91.7 97.2 (i 71 2586 96.8 8 78 2438 10 64 2325 97.3
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ANALYTICAL CHEMISTRY
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RESULTS AND DISCUSSION
Analysis of eight samples of reactor cooling water yielded a n average recovery of 98,9yo of the Zn65, with a standard deviation of 4.7%, of which 2.501, was due to the statistical counting error. A y-ray!pectrum of the radioisotopes present in 2 ml. of the sample is presented in Figure 1,A, and a typical spectrum of t h e isolated product is shown in Figure 1,B. Effective decontamination was obtained from all isotopes except CuB4and A h " . The amount of MnS6 transferred to the amalgam caused a positive error of only 2% in the zinc counting channels due to the Compton contribution, and repre5ents a M n a decontamination factor of 4.5 X lo3. This would not be a serious interference in monitoring applications. The Cu64in the sample was transferred quantitatively to the amalgam subsequent t o reduction by the zinc. This isotope also contributed to the counting rate in the Zn66channels and introduced a positive error of about 10%. Corrections for these errors can be made by a set of simultaneous equations for purposes of absolute assay of the Zn65 concentration in any given sample. When it is necessary to obtain radio-
'
-CADMIUM
Procedure. A 100-ml. sample of reactor cooling water was made O.1M in tartaric acid and was added t o 6 ml. of stock amalgam in a 125-ml. separatory funnel. The mixture was agitated for 8 minutes on a mechanical wrist shaker. The amalgam phase was separated into a suitable container and counted on a y-ray spectrometep.
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2 ml. of reactor cooling water Zinc amalgam extract from 100 mi. of reactor cooling water Showing effect of pre-extraction with cadmium amalgam on product purity
chemically pure isotopes, as Zn69m, the Cua4can be removed by pre-extraction into cadmium amalgam. The cadmium amalgam, prepared in the same manner and ratio as the zinc amalgam, will reduce and extract the copper, and leave the radiozinc in solution. A sample treated in this manner is compared with a single zinc amalgam extraction in Figure 1,C. The pre-extraction did not affect the radiozinc recovery, and made possible the measurement of Zn69m. The influence of electrolytes other than tartaric acid on the zinc amalgam exchange was tested by agitating the amalgam for 5 minutes with spiked solutions of the various reagents. Ammonium hydroxide in the concentra-
tion range of 0.1 to 1M and 111f HC1 did not differ significantly from 0.1M tartaric acid. Molar solutions of H2S04, "03, NaC1, and Na2SO4 reduced the Zn65recovery to 70 to 80%. If analysis were required from such a matrix, a predetermination of the yield under standard conditions n-ould permit the application of amalgam exchange. The counting efficiency for Zn6.J was lowered by about 1570 by counting the mercury phase, because of attenuation of the y-rays. To compensate for this error, a correction factor could be applied, or the zinc could be transferred to a n aqueous phase by back extraction into an acid solution containing cupric ions. This could either be counted
directly, or evaporated to a small volume to provide a higher counting geometry. The advantages of this method are the simplicity, rapidity, and selectivit) by which radioactive zinc can be recovered from reactor cooling water. The usefulness of amalgam exchange extends beyond this immediate application and
adaption to a number of additional radioisotopes is suggested. LITERATURE CITED
(1) Chipman, IT-,
A., Rice, T. R., Price, T. J., Fishery Bull. 135, Fish and Wild Life Service, U. s. Department of the
Interior, 1958. ( 2 ) &Toe, J. R., Kim, C. K., Meinke,
R.iv., Z'alanta 3,298-9 (1960). (3) Morse, H. N.,Burton, W. M., A m . Chem. J . 10,321 (1888). (4) Perkins, R. W., Wielsen, J. M , Scrence 129, 94-5 (1959). ( 5 ) Ibzd., to be published. RECEIVED for review July 2, 1960. Accepted November 4, 1960. Work performed under Contract KO.,4T(45-1)-1350 for the U. S.Atomic Energy Commission.
Solvent Extraction Method for the Radiochemical Determination of Zinc WILLIAM J. MAECK, MAXINE ELLIOTT KUSSY, and JAMES E. REIN Phillips Petroleum Co., Atomic Energy Division, ldaho Falls, Idaho This method for the determination of radiozinc in fission product mixtures is based on strong base scavenging of basic medium insoluble ions with amphoteric zinc remaining in solution, followed by solvent extraction of the diethyldithiocarbamate complex into ethyl acetate. Zinc is removed from the organic phase by stripping with dilute hydrochloric acid. The yield determination is based on an EDTA titration with Eriochrome Black T indicator. Counting is done in a welltype Nal(TI) scintillation crystal. The method was evaluated by measuring the fission yield of zinc-72 in a thermal neutron irradiated sample of uranium235. A value of 2.6 X lO-'% is reported.
R
especially aluminum-clad, often contain zinc as an impurity in the cladding. Because corrosion of fuel cladding is a serious problem in nuclear reactor operation, reactor coolant waters are routinely analyzed for various corrosion products. The zinc activity encounterrd and usually analyzed for is zinc-65 produced by neutron capture. While many methods are available for the determination of nonradioactive zinc,, few procedures exist for the radiochemical determination of zinc in fission product or radioactive corrosion product solutions. Siegcl and Glendenin ( 7 ) have reported a procedure for the isolation of zinc activity from fission products based on repcated precipitations of zinc mercuric thiocyanate. A reliable but lengthy ion exchange separation has also been reported ( 1 ) . After the completion of the work reported in this paper, Silker (8) reported a method for the separation of zinc-65 from reactor cooling waters by isotopic exchange 11 ith zinc amalgam. A simple solvent extraction procedure has not been noted in the literature, and because EACTOR FUEL ELEMENTS,
this technique is generally simple and efficient, this study was undertaken to develop one. The method is based upon a preliminary separation of most hydrolyzable ions from amphoteric zinc with strong caustic folloffed by extraction of the diethyldithiocarbamate complex of zinc into ethyl acetate. EXPERIMENTAL
Apparatus. A 3 X 3 inch SaI(T1) well-type scintillation crystal coupled to a 256-channel pulse height analyzer vr as used for all counting. p H measurements were made with a Leeds &. Northrup miniature needletype pH electrode assembly. Reagents. .\nalytical grade reagents vere used throughout ivithout purification. Fission product mixtures n ere prepared by irradiating highly enriched uranium in the Materials TestingReactor. The zinc carrier solution was Dreixred by dissolving sufficient Zn(kO,j? in 0.1A- HKO, to make a 0.05X solution. The carrier solution was standardized with an EDTA titration as described in the procedure. Procedure. Pipet a sample aliquot into a 50-nil. centrifuge tube containing 5 ml. of 0.05M zinc carrier solution, dilute to about 20 ml. n i t h water, and acidify with perchloric acid if the sclution is basic. A4dd 0.5 nil. of 0.05X Ce(1V) in 1111 perchloric acid and heat to just belolv boiling until the color changes from amber to pale yellow. Do not boil as the solution may froth out of the tube. Add 3 ml. or more if necessary of 1OA' NaOH to obtain a pH of 14. Centrifuge and transfer the supernatant liquid to a clean 50-ml. centrifuge tube. Discard the precipitate. Acidify with SA' HC1 until the maximum amount of precipitate is formed (which occurs a t pH 8.2). A convenient means of adjusting the pH is to use a magnetic stirrer and a needle-type pH electrode assembly. (Indicators interfere with the final yield determination.) Centri-
fuge and discard the supernatant solution. Wash the precipitate with water, centrifuge, and discard the supernatant solution. Add concentrated NHdOH to dissolve the precipitate. Aluminum if present remains precipitated, but does not interfere. Transfer t o a 125-ml. separatory funnel with a 5- to IO-ml. water wash. Add 4 ml. of an aqueous 6% solution of sodium diethyldithiocarbamate, 50 ml. of ethyl acetate, and extract for 5 minutes. Discard the aqueous phase and pipet as much as possible of the organic phase to a clean 125-ml. separatory funnel. Strip for 3 minutes with 25 ml. of 0.2147 HCl. Drain the strip into a 100-ml. beaker and adjust to p H 9.5 with concentrated NH40H. iidd 2 drops of 0.2% Eriochrome Black T in nitrilotriethanol and titrate with 0.05,11 EDTA from the purple to blue end point. Transfer the titrated sample to a suitable tube for counting in a well crystal. DISCUSSION
Past experience in this laboratory has indicated that extractions of fission product complexes are more selective from basic media than from acidic media. Of the solvent extraction systems for zinc described in the literature (4, 6), the extraction of zinc diethyldithiocarbamate from an ammoniacal medium was thus selected. The amphotericism of zinc provides a convenient means of scavenging fission products that form insoluble hydroxides from a strongly basic medium. Iron (111)was initially tried as the scavenger. With fission product mixtures excessive amounts of ruthenium carried along with the zinc in the extraction. The substitution of Ce(1V) for Fe(II1) plus heating in an acidic medium prior to the basic precipitation satisfactorily decreased the extraction of ruthenium. This is attributed to oxidation of ruthenium to an oxidation state which appears to carry with the cerium precipitate. The scavenging action of cerium was as efficient as that of iron. VOL. 33, NO. 2, FEBRUARY 1961
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