Dissolution of γ-irradiated sodium chloride and potassium sulphate powders in pure water and aqueous sodium nitrate solution results in the emission of light in the former, and the formation of nitrite in the latter case. Appropriate mechanisms have been suggested for the luminescence and NO
 2
 −
 formation in the light of the known radiolytic products formed in the salts during the irradiation. The photoannealing of the irradiated sodium chloride under the influence of visible light and K2SO4 by visible ultraviolet and laser lights has been studied by monitoring the changes in the NO
 2
 −
 yield with annealing times. The observed changes in the nitrite yields have been correlated with the bleaching of the radiolytic products during the photoannealing of these salts.

A comparative study on aqualuminescence, chemical effects and photoannealing of γ-irradiated NaCl and K2SO4

Dissolution of γ-irradiated chlorides of sodium and potassium in a solution of NaNO3 and KI results in the formation of NO
 2
 −
 and iodine as stable products. The variation in the yields of the products with the amount of irradiated salts is studied. The effect of photoannealing of the irradiated salts on the yields of nitrate and iodine in the mixture is discussed on the basis of photoannealing reactions of the colour centres.

Chemical effects induced by γ-irradiated alkali halides in aqueous binary mixtures of nitrates and iodides

Electrical conductivity and Seebeck voltage developed in thermally pretreated and γ-irradiated TiO2 was measured as a function of temperature. The conversion of n-type TiO2 into p-type and vice versa observed after irradiation was explained in terms of ionization of Ti3+ donors and lattice O= species, subsequent trapping of carriers in adsorbed oxygen and further formation of p-type inversion layer on the oxide surface during irradiation. The sign of the EMF of the electrochemical Ag/Ag+ concentration cell by the addition of heated and γ-irradiated TiO2 in one of the compartment of the cell was found to be opposite to that due to the addition of the corresponding heated but non-irradiated oxide sample.

Electrical and electrochemical properties of pretreated thermally and γ-irradiated TiO2

Reduction of nitrate to nitrite takes place when the stored energy in the form of colour centres is released during dissolution of γ-irradiated NaCl crystals in aqueous sodium nitrate solution. Various parameters like dose, amount, storage time and particle size of irradiated NaCl salt which control the yield of nitrite have been studied. Similarly, the effect of concentration of NaNO3 and the role of precipitation on the yields of nitrite in aqueous TlNO3 and AgNO3 have been investigated. The energy transfer parameter has been determined as the ratio of G/NO
 2
 −
 / obtained by the addition of irradiated NaCl to that of direct γ-radiolysis. The data permit the evaluation of the concentration of colour centres in the irradiated NaCl crystals on the basis of the mechanism of reduction of nitrate.

Reduction of nitrate during release of stored energy from γ-irradiated NaCl crystals in aqueous NaNO3 solution

It is well known that paramagnetic centers are formed when Na2SO4 crystals are exposed to -radiation. The dissolution of such crystals in aqueous ammonium nitrate results in reduction of nitrate to nitrite. Various factors which influence the yield of nitrite are investigated. The yield of nitrite is found to vary with the amount of irradiated Na2SO4 added, the dose absorbed by Na2SO4 crystals, the storing period of the irradiated salt, photoannealing time, concentration of aqueous ammonium nitrate and particle size of the Na2SO4 crystals. The G(NO 2 – ) value under optimum conditions of the conversion of nitrate to nitrite by irradiated Na2SO4 in aqueous ammonium nitrate is 0.009. The efficiency of energy transfer is 1.5%. The mechanism of reduction is based on the reactions of paramagnetic centers with nitrate ions.

Chemical effects induced by γ-irradiated Na2So4 in aqueous ammonium nitrate

F → M phototransformation in γ-irradiated NaCl was found to be accompanied by a lower intensity of aquoluminescence and a greater liberation of I2 during the dissolution of the sample in water and in KI solution, respectively. The results are explained on the basis of the different reactions of F and M centres with water during dissolution yielding e–aq due to F and (e–22)aq, a dimer or (e–aq+e–aq) and some complex species due to M centres.

Effect of F → M phototransformation on aquoluminescence from γ-irradiated sodium chloride

Photoconductivity in γ-irradiated alkali halides

Cathodic process in electrolytic coloration of NaCl and KCl

Direct evidence for this type of chemical change was obtained from the following experiments: Ten g of a dry sample of ZnO (BDH, 200 mesh) with adsorbed oxygen was placed in a glass sparger and the air in it was removed by a continuous flow of N2 at a rate of 60 ml per min. The sample was then contained in an N2 atmosphere and irradiated by gamma rays from a 6 0 Co source to the desired dose. The dose was measured by Fricke's dosimetry at room temperature (25 °C). After irradiation the sample was swept with a flowing N2 carrier gas which was allowed to flow through a gas chromatographic column. The 0 2 desorbed due to the irradiation was estimated quantitatively by gas chromatography using a sensitive detector [2]. The sample was then enclosed in an N2 atmosphere and the temperature was rapidly raised from 25 to 100°C and maintained at 100°C for a period of one hour. The N2 gas containing the 0 2 desorbed at 100°C was analyzed as described above, and the amount of 0 2 was estimated. The same sample, still was again enclosed in an N2 atmosphere and was further heated from 100 to 200 and the analysis for 0 2 was repeated. After one hour the procedure was repeated after raising the temperature to 300 °C and the amount of desorbed 0 2 was estimated as before. In this way the desorbed 0 2 from the surface of irradiated ZnO was estimated at 25,100, 200 and 300°C. The same procedure was adopted for the Fig. 1. Changes in the peaks of 0 2 desorbed at (A) 100, (B) 200 and (C) 300°C from the surface of the gamma irradiated ZnO

H. J. Arnikar

Papers

Effect of F → M phototransformation on aquoluminescence from γ-irradiated sodium chloride

Photoconductivity in γ-irradiated alkali halides

Cathodic process in electrolytic coloration of NaCl and KCl

Gamma-Radiolytic Changes in the Chemical State of the Adsorbed Oxygen over Zinc Oxide