Chemical Behavior of Carrier Free Iodine Produced by Beta-Decay and Effects of Iodine Carriers

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1 Journal of NUCLEAR SCIENCE and TECHNOLOGY. 7 [2] p. (February 1970). Chemical Behavior of Carrier Free Iodine Produced by Beta-Decay and Effects of Iodine Carriers Tetsuo HASHIMOTO*, Tadaharu TAMAI*, Rokuji MATSUSHITA* and Yoshiyuki KISO* Received September 10, 1969 The effect of carriers on the chemical behavior of 131I produced from the 130Te(n, r)131te-> I processes was investigated with paper electrophoresis, autoradiography and 131r-ray spectrometry. If no carrier was added, the chromatograms of the iodine species revealed significant deposits of an unexpected chemical species between the spots of the iodide and iodate species. The addition of either iodate or periodate as carrier converted the species into iodate in the former case, and into iodate and periodate in the latter. Referring to the already known exchange reactions between different iodine species, hence was concluded that the species observed in the experiment without carrier was the iodite species (10+2), as surmised by previous authors. I. INTRODUCTION Radioactive 'I can be appropriately produced by neutron capture of Te followed by a subsequent b-decay or obtained as nuclear fission productsc(1). However, after these procedures efficacious recovery of the 131I from the target material is difficult, because the chemical states are unstable without addition of carriers(2). Separation with carrier has been tried by many authors(3)~(6), from different radioactive nuclides. While this expedient may simplify the chemical separation of iodine, the resulting products are liable to be influenced by the carriers. Object of the present experiment is to elucidate the effect of carriers on the distribution of iodine species. In order to produced in carrier free concentration, Te compounds as K2TeO4, H2TeO4 and K2TeO3 were irradiated with thermal neutrons in a flux of 5x 1012nlcm2 sec. After the decay of short lived Te (24.8 min), the iodine species were sepa- 131 rated by paper electrophoresis. The radioactivity of 131I on the chromatogram was determined by means of r-ray spectrometry. The distribution of radioactive iodine species was obtained as a function of the carrier concentration and the irradiation period. The chemical state of an unexpected iodine species observed on the chromatogram is discussed based on the experimentally obtained data and referring to the already known exchange reactions between different iodine species(7)(8). II. 1. Materials EXPERIMENTAL Powdered telluric acid was purchased from Mitsuwa Chemicals Co.; potassium tellurate and potassium hypotellurate from Wako Chemicals Co. The results of paper electrophoresis and neutron activation analysis indicated that the purity of these reagents was satisfactory for the present experiments and hence they were used without further purification. All other chemicals used were guaranteed grade. 2. Neutron Irradiation Solid (ca. 100 mg) and liquid (ca. 0.1 ml of a 0.5 M solution) samples were sealed in polyethylene vials, placed in a large polyethylene capsule, and irradiated under a thermal neutron flux of 4.7 x 1012n/cm2-sec in the pneumatic tube of the Kyoto University Reactor (KUR). The Cd ratio at the irradiation position was 5.7, the r-dose rate at 1 MW operation 2.7x 107R/hr, and the temperature about 40dc. The irradiation was continued for 2~120min. * Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka. 32

Vol. 7. No. 2 (Feb. 1970) 93 3. Method of Chemical Separation The irradiated samples were kept for about 12 hr at dry ice temperature until the short lived radioactive Te was decayed completely.

2 Vol. 7. No. 2 (Feb. 1970) Method of Chemical Separation The irradiated samples were kept for about 12 hr at dry ice temperature until the short lived radioactive Te was decayed completely. The decomposition of the samples before analysis was avoided by storage at low temperature. Then, the samples were dissolved in 0.5 ml distilled water and an aliquot of the solution was subjected to paper electorophoresis. An apparatus with multicells was used(9). As background electrolyte a 1N NaOH solution was selected for the separation of iodine species(10)(11). After dipping a paper strip in the background electrolyte solution and removing the excess solution with another paper, about 5 ml of solution containing the irradiated sample was placed on filter paper (Toyo Roshi No. 50, 1 x40 cm). A potential gradient of 200 V/30 cm was applied for 1 hr. The temperature of the migration cell was kept at 10dc by circulating cooling water, to prevent the thermal decomposition of the sample during the migration. After the migration, the chromatogram was dried in an electrical oven for about 10min, and then subjected to autoradiography. 4. Autoradiography and Radioactivity Measurement The distribution pattern of radioactivity on the paper was examined by autoradiography using a Fuji medical X-ray film. The paper strips were cut into a number of segments, each corresponding to one chemical species, on the basis of visual observation of the autoradiogram. The r-ray spectrum of each sample was determined with a TMC- 400 channel pulse height analyzer connected to a well type (NaI) scintillation crystal. The 364 kev photopeak was used for the measurement of 131I. 5. Identification of Iodine Species on Autoradiograms Neutron irradiated iodine compounds such as NH4I, KIO3 and KIO4 were used for identifying the migrated iodine species. It is known that iodine changes from the higher to the lower states of oxidation by the hot atom effect based on the 127I(n,r)128I reaction(12) so that one can obtain all of the labeled iodine species from the irradiated compounds mentioned above. Some typical autoradiograms are shown in Photo 1. Photo. 1 Autoradiograms of radioactive iodine species obtained from Te and I compounds irradiated in reactor The migration behavior of the different iodine species was found to agree fairly well with what has been reported by Gordon-. From these migration patterns, the migration velocity of I and Te compounds falls into the following sequence: I->TeO3->IO3- >IO4-=TeO4-. In the case of electrophoretic run without addition of carriers, considerable radioactivity was often found between the spots I- and IO3 on the paper strip. The reason will be discussed in the following chapter. III. RESULTS AND DISCUSSION The distribution of iodine species in different oxidation states produced from three Te compounds are shown in Fig. 1, where iodide, iodate and periodate were identified by the migration patterns of iodine species produced by the 127I(n, r)128i reaction as already described. When free of carrier, in addition to these species, an unidentified fourth species (which we shall name *X) was usually found at a position lying between iodate and iodide on the chromatographed paper. Hexavalent tellurium, such as telluric acid and its salt, forms a larger proportion of higher valency iodine species compared with 33

3 94 J. Nucl. Sci. Technol., acid would be markedly affected by surrounding substances such as decomposition products and target materials. The *X species was found among the iodine species obtained from all Te compounds, and the yield of the species was found to be as such as 74% in the case of potassium tellurate. The reproducibility of distribution however was always poor. This evidences that this species would be very unstable. In order to examine the species in detail, three kinds of iodine carriers were added to a carrier-free solution, and the effect of carrier on the yield of the iodine species was observed in the same way as without carrier. The results obtained are shown in Figs. 1 and 2. Fig. 1 Effect of I carriers on oxidation states of 131I tetravalent tellurium. This can be explained as follows: When the radioactive parent Te decays into its daughter iodine, the chemical bond between Te and O partly remains as that between I and 0. In fact, most of the "'re was found after the neutron capture in the same valency state as that of the original Te. The tendency of the hexavalent tellurium (K2TeO4 and H2TeO4) to produce a larger proportion of higher valency iodine species (IO4- IO3-) is well revealed in Fig. 1. However, there are some differences between the distribution of four kinds of iodine species. The ph value of the aqueous solution of the neutron irradiated compounds exceeded 12 for potassium tellurate and 3.5 for telluric acid. Chemical reactions between iodine and other species take place more freely in acid than in alkaline solution(13). This would indicate that products resulting from telluric Fig. 2 Effect of carrier concentration on oxidation states of 131I These figures reveal the following facts: The addition of carrier iodine tends to diminish the *X species on the chromatogram strip, and converts it mostly into iodate and periodate. On the other hand, the yield of iodide species is not affected by the addition of iodide carrier, which transforms the *X 34

4 Vol. 7, No. 2 (Feb. 1970) 95 species in potassium tellurate into iodate. This precludes the possibility of species being hypoiodite (IO-), because hypoiodite would undergo rapid isotopic exchange reaction with iodide species(7) : where the asterisk ( *) indicates a radioactive species. The concentrating effect of I carriers on the *X species was also examined, as shown in Fig. 2. The amount of iodate and periodate carriers was varied from to 0.1 M. The *X species is affected even by the smallest amounts of carrier (0.001 M) considered practically as carrier concentration(14). The results obtained with iodate carrier are suggestive of the reaction which converts most of the *X species into the same chemical form as the carrier. The periodate species increases with increasing concentration of periodate. The results in Fig. 2 suggest neutron irradiation time. The yield of the *X species attains maximum value at about 30 min after the start of irradiation and then decreases with irradiation time. The iodide species, on the other hand, is seen to increase continuously with irradiation time. This would indicate that the *X species can be converted into iodide and iodate species by long irradiation. The *X species is reduced by certain substances derived from radiolysis of the target material such as metallic Te(15). On the basis of the foregoing results, and in consideration of its migration behavior, it is indicated that iodite (IO2-) would be the identity of the *X species. This is in fact what was previously surmised by other authors in the course of studies in the hot chemistry of iodine (6)(16) and in the chemistry of 131I at low concentrations(17). The present confirmation of these previous reports is validated by the fact that the experiments were facilitated by the treatment without carrier. Arnikar et al. have studied the isotopic exchange reaction between iodide and iodate species by chromatography, and report that the reaction rate is very slow even at 240dc(8). Such a reaction is beyond consideration in the present experiments at room temperature. Figure 3 shows the variation of the yield for the four iodine species as a function of Fig. 3 Distribution of oxidation states of '"I as a function of irradiation time in a reactor REFERENCES (1) KAHN, M.: "Inorganic Isotope Synthesis", 227 (1962), W.A. Benjamin, Inc. (2) INARIDA, M.: J. Chem. Soc. Japan, Pure Chemistry, 84, 731 (1963). (3) STEVOVIC, J., JACIMERIC, L., VELJKOVIC, S.: J. Inorg. Nucl. Chem., 27, 29 (1965). (4) ORTEGA, J. : ibid., 28, 668 (1966). (5) KRONRAD, L.: Radiochim. Acta, 3, 191 (1964). (6) BERTET, P.M., CHANUT, Y., MUXART, R.: ibid., 2, 116 (1964). (7) HELLAUER, H., SPITZY, H.: Biochem. Z., 325, 40 (1953). (8) ARNIKAR, H. J., TRIPATHI, R.: J. Chromatog., 7, 362 (1962). (9) KISO, Y.: J. Sci. Hiroshima Univ., Ser. A-II, 27, 24 (1963). UKLA, (10) S.K., SH BACHER, M., ADOLOFF, J.P.:J. Chromatog., 10, 93 (1963). ) GORDON, B. M.: J. Inorg. (11 Nucl. Chem., 29, 287 (1967). (12) TEN, AA. H. W., Komi, G.K., Jr., W ESSELINK, G.A., et al.: J. Amer. Chem. Soc., 79, 63 (1957). 35

5 96 J. Nucl. Sci. Technol., (13) GUTMANN, V.: "Halogen Chemistry", Vol. 1, p. 83 (1967), Academic Press. (14) CUMMISKY, B. C., HAMILL, W. H., WILLIAMS, R., Jr. : J. Inorg. Nucl. Chem., 21, 250 (1961). (15) CONSTANT, R.: Proc. znd Geneva Conf., 28, 117 (1958). (16) CLEARY, R E., HAMILL, W. H., ni ILLIAMS, R.R., Jr. : J. Amer. Chem. Soc., 74, 4675 (1952). (17) KAHN, M., WAHL, A. C. : J. Chem. Phys., 21, 1185 (1953). 36

Production of Fluorine-18 by Small Research Reactor

Journal of NUCLEAR SCIENCE and TECHNOLOGY, 4[4], p.185~189 (April 1967). 185 Production of Fluorine-18 by Small Research Reactor Yoshiaki MARUYAMA* Received October 4, 1966 High purity 18F was prepared