Indian Journal of Chemistry Vol. 22A,June 1983,pp. 514-515 Studies on Recoil Chemistry of Iodine-128 The distribution of 1281 activity in various in Aqueous Sodium Periodate Solution radioactive products during radiolysis ofaq. Nal04 in under (n, y) Process] the presence of additives is given in Table I. The yields of radioiodide and radioperiodate fractions increase with increase in [additive], whereas, that of s P MISHRA*, R TRIPATHI & R B SHARMA radioiodide fraction decreases. Also, with increase in Department of Chemistry, Banaras Hindu University, Varanasi 221005 [additive], the radio-iodate, -iodide and -periodate yields reach the limiting values of about 36, 50 and 16% Received 16July 1981,revised II October 1982;accepted 5 November 1982 respectively. It is difficult to provide quantitative treatment of per 128 128 The retention of 1 in the form of 104- ions following(n, y) cent yields of stable end products of recoil 1 in the process,in aqueous solutions of Na104, has been measuredin the form of 1-, 103 and 10i on the basis of various presenceof chloride and acetate additives.The retention value in models of reentry processes. It appears that the crystallineNaI04 at room temperature (25°C)is-4% whereas in aqueous solution irradiated at 25°C and also at liquid nitrogen ultimate fate of recoil atoms is mainly decided by temperature the values are 6.9 and 15% respectively.Yields of chemical reactions. In aqueous solution the target ions radioperiodateand radioiodidefractionsincreasewith the increase are surrounded by large number of water molecules in [additive] whereas that of radioiodate fraction decreases.The and except in very concentrated solutions the results are explained in the light of a model which invokes the probability that 1281 atoms will hit an inactive target oxidizing-reducingnature of the intermediates produced during ion in a hot collision is much smaller, because of a large neutron irradiation. separation between a pair of 10i ions. In 0.07 Miodate A large volume of work on the chemical effects and 0.065 M periodate solutions the distance between following (n, y) recoil has been carried out on organic two target ions is a little more than 20 A which systems, both in liquid and vapour phases; but only decreases to about 10 A with increase in [additive] (see little is known about the recoil chemistry of 1281 in ref. 7). solution phase 1. Cleary et al? and Arnikar et al+" The effect of ionizing radiation on water depends to reported the yields of only radioiodate and radioiodide some extent upon the experimental conditions and the but radioperiodate fraction was detected by these nature of the radiation. However, the main radiolytic authors. Bellido ' was able to collect 8% of products are H202, H, H2, OH, e,;q, H02 etc. The radioperiodate fraction from neutron irradiation of primary oxidizing species are OH and H02 and H202 aqueous Nal03 in the presence of periodate carriers. being a secondary product. The present work has been undertaken for The irradiation of aqueous periodate solution with comparing the contribution of various physical and (n, y) most probably, yields r ': I ,10,102 etc. as the chemical processes on the observed data both in reactive intermediates which are finally converted into crystalline and aqueous phases and to arrive at a radio-iodide, -iodate and -periodate. Cleary et at? 128 reasonable explanation ill the light of new showed that quite a large fraction of the recoil 1 information. atoms is initially in zero state of oxidation except in The aqueous solutions of target (NaI04) were case of internal conversion. The presence of 10 and irradiated with thermal neutrons from a 300 mCi (Ra 102 in aqueous solutions was confirmed spectro- + Be) source with an integrated flux of 3.2 x 106 2 n/s/cm . The irradiation of frozen aqueous phase was Table I-Distribution of 1281 Activity in 1-, 103 and 10; carried out in a sealed soda glass tube dipped in liquid Ions Produced during Thermal Neutron Irradiation of nitrogen ( -196°C) along with the neutron source. The Nal04 additives used were KCI, NaCI, KOAc and NaOAc. Phase [NaI04] % Activitydistribution The three stable radioactive products, i.e. iodide, M iodate and periodate were separated by fractional 10 ;, 103 1- precipitation and solvent extraction methods". Crystallinesolid 0.00 3.9 84.8 11.3 (25 C) Frozen aqueous phase 0.07 14.5 61.5 24.0 tPresented at the Nuclear and Radiation ChemistrySymposium, (-196°C) held under the auspices of Department of Atomic Energy, Aqueous solution 0.07 6.9 78.4 14.7 Government of India during 25-28 February 1980 at Andhra (25°C) University,Waltair. 514 NOTES metrically". Probably the oxygenated iodine species responsible for the high yield of radioiodate both in are mainly formed from positively charged iodine solid and aqueous phases. atoms. Liebhafsky" proposed + 3 oxidation state of Further, increase of retention with increase in iodine (as HIOz) as an intermediate to explain the concentration'v" of target Nal04 and with the increase oxidation of 1 - to 103-, Henley and Johnson!", on in [additive] can be explained on the basis of the thermodynamic considerations, showed that the exchange reaction (12) primary oxidizing species OH and H0 (oxidation 2 1*02- + 104- -> I*04- + 102- ••. (12) potentials 2.8 and 1.35 V respectively) should be The hot zone of small volume will contain some capable of oxidizing all these intermediate iodine inactive target ions along with radioactive recoil species to 104-, The reaction mechanism shown in species so that exchange reactions are probable Scheme 1 envisages successive oxidation of(n, y) recoil following the radio lytic oxidation reactions. With 1281 species. Scheme 1 indicates that the formation of increase in additive the dimension of the hot volume various radioiodine fragments ~n higher oxidation tends to be more compact and thus increases the states depends on the availability ofOH radicals as are probability of some more high energetic atoms to be expected from local radio lysis as well as internal trapped within this small volume. Also, from a conversion (Auger charging). Some H 0 (OH +OH) 2 2 viewpoint of radiolysis, the additives may take part in may also be formed arid according to Haissinskyll, chemical reactions affecting retention. In the presence H 0 (OH +OH) if produced, will reduce the 2 2 of acetates, probably the oxidizing radical OH is not intermediate radioiodite ion in accordance with Eq. destroyed. At higher concentrations of acetate (II). additives the deviation in activity distribution may be due to association of acetate ions, which subsequently *1- + OH -> *1 + OH- (1) react with OH radicals to afford compounds (like *1+ OH -> H*IO (2) acetone) rather than peracetate ion. H*IO + OR -> *~O + H 0->H*IO;+H+ (3) 2 We thank the UGC, New Delhi for financial H*IO + Ha -> *10 + H 0 (4) 2 2 2 support. *10 + GH -> H*102 -> *10; + H + (5) *10; + aH -> *10 + HO; (6) 2 2 References H*IO; + Ha -> *10; + H 0 (7) 2 2 1 Ambe F & Saito N, Radiochim Acta, 13 (1970) 105. *102 + GH -> H*103 -> *10; + H + (8) 2 Cleary R E, Hamill W H & Williams R R, JAm chem Soc, 74 *10; + Ha2-> *193 + HO; (9) (1952) 4675. 3 Arnikar H J, Dedgaonkar V G & Shrestha K K, J Unio Poona, *103 + GH -> *10"4 + H+ (10) Sci and Tech See, 38 (1970) 169. 4 Arnikar H J, Dedgaonkar V G & Shrestha K K, J Uniu Poona, Scheme 1 Sci and Tech See, 38 (1970) 177. 5 Bellido A V, Radiochim Acta, 7 (1970) 122. ... (11) 6 Boyd G E & Larson Q V, JAm chem Soc, 91 (1969) 4639 . 7 Robinson R A & Stokes R H, Electrolyte Solutions (Butterworths, London) 1955, 16. Hence, it follows that destruction of the intermediate 8 Amichai 0 & Treinin A, J phys Chem, 74 (1970) 830. diminishes the probability of formation of radio- 9 Liebhafsky H A, JAm chem Soc, 53 (1931) 2074. iodates and radioperiodates. This might be the cause 10 Henley E J & Johnson E R, The chemistry and physics of high energy reactions, (Univ Press, Washington DC). for the relatively low values of radioperiodate found 11 Haissinsky M, Jove J & Szymansky W, J chem Phys, (1964) 272. from aqueous periodate at low concentration. 12 Garrison W M, Bennett W,ColeS,HaymondH R&Boyd MW, However, periodate itself being an oxidizing agent is J Am chem Soc, 77 (1955) 2720. 515.