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. pH 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 pH 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
0
235
The interference of ruthenium in many fission product solvent extraction systems is well known. The use of Ce(1V) as a combined oxidant and scavenger offers advantages for such systems. However, Ce(1V) may oxidize the ion of interest to a nonextractable state or form a n insoluble complex. -4fter scarenging, the p H of the solution was lowered to approximately 8.2 to precipitate zinc and improve the decontamination. dluminum, if present, will also precipitate at this pH, but does not interfere. The zinc precipitate \X as dissolved in ammonia, diethyldithiocarbamate was added, and the zinc complex was eltracted into ethyl acetate. Ethyl acetate, with a density lower than that of water. iTas chosen as the solvent rather than chloroform (4) to simplify the procedure. After extraction, the zinc was stripped with dilute hydrochloric acid in a separate separatory funnel for higher decontamination. The transfer was made with a pipet rather than draining the organic through the stem of the first separatory funnel. If extremely high decontaniination is not required. this strip niay be done in the original separatory funnel. The high degree of decontamination, using two separatory funnels, is shown in Figure 1. The yield determination n a s conveniently performed by adjusting the strip phase to p H 9.5 and titrating with EDTA to the Eriochrome Black T end point. Errors associated with a gravimetric yield are thus eliminated. ilfter titration, the sample v a s counted in a well-type scintillation crystal. The average yield was approximately 60%. h proposed radiochemical inethod for a n element which has a fission product isotope can be evaluated by confirming the U235 thermal neutron fission yield value. Confirmation indicates purity of separation and that chemical identity was attained between the sample and Mog9appears to be the most carrier suitable isotope to establish the number of fission events which have occurred. Its fission yield of 6.06% ( 2 ) is fairly well k n o w and the analysis is simple. Measurement of the 1.62-m.e.v. gamma peak of Lala groning in from a separated BaI4O fraction is often used as a fission monitor. Because some question exists as t o the branching ratio through this level, Mog9is preferred as a fission monitor in this laboratory. The proposed method was evaluated by measuring the U235thermal fission yield of 211’2. Three aliquots of a 4day-old fission product mixture, each containing approximately 2 X l O I 4 fissions based on Nog9 analyses, were carried through the procedure. GaT2 \\as allowed to grow in, and the 0.835m.e.v. ganima peak was analyzed 50 and 120 hours after the zinc separation. 236
ANALYTICAL CHEMISTRY
--
Figure 1. Distribution of fission product activity in method
E
IO‘
IO2 SEPARATED Zn FRACTION
IO
o
0.1
0 2 03 04 05 06 07 aa 09 IO II 12 1 3 1 4 ENERGY (hlE.V.)
The data from both times agreed and are given in Table I. A photon abundance of 81 per 100 disintegrations (3) was used in the calculations. The gamma spectrum of the zinc fraction 50 hours after separation is shown in Figure 1. The Ga72 peak analyzed is designated. No claim is made that the (Table I) value of 2.6 f 0.3 x is more reliable than the 1.6 X value reported several years ago by Siegel and Glendenin (6). The fact that the values are reasonably close indicates the degree of decontamination and reliability associated with the proposed method. Fission Yield Value of Zn7’ Table I. Based on the Proposed Method
Time After Zn Sepn.,
Hours 50 120
Sample, %, X 1
2.6 2.2
2 2.8 2.5
3
2.5 2.9
Average,* %, x 10-5 2.6 2.5
5 Computed absolute standard deviation for a single determination is 10%.
LITERATURE CITED
(I) Hicks, H. G., Stevenson, P. C., Nethaaay, D. R., U. S. Atomic Energy Commission, ReDt. UCRL-4377 (1954). (2) Katcoff, Seymour, Nucleonics 16, No. 4, 73 (1958). (3) Miller, C. F., U. S. Atomic Energy Commission, Rept. USNRDL-TR-160 (1957).. (4) Morrison, G. H., Freiser, Henry,
“Solvent Extraction in Analytical Chemistry,” Wiley, New York, 1957. (5) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” Interscience, X‘ew York, 1959. (6) Siegel, J. M., Glendenin, L. E , “Radiochemical Studies: The Fission Products, Book 3,” C. D. Coryell and N. Sugerman, eds., National Kuclear Energy Series, Division IV, Vol. 9, Paper 53, McGraw-Hill, Xem- York, 1951. (7) Zbid., Paper 226. (8) Silker, W. B., Paper 10, Analytical
Division, Northwest ACS Regional PIIeeting, Richland, Washington, 1960.
RECEIVED for review August 15, 1960. Accepted November 1, 1960. Division of Analytical Chemistry, 138th Meeting, ACS, New York, N. Y., September 1960. Work done under Contract At (10-1)-205, for the U. S. Atomic, Energy Commis51011.
