QUANTITATIVE STUDY OF FORMATION OF FREE I2 MOLECULES IN GAMMA-IRRADIATED MICROCRYSTALLINE POWDERS OF PURE AND DOPED POTASSIUM-IODIDE

Photodecomposition of pure and doped KI powders [KI:Cs, KI:Rb, KI:Na, KI:Cl, KI:Br, KI:RbCl, KI:RbBr, KI:NaCl, impurity concentration 500 p. p.m.] to produce free I2 molecules during gamma irradiation is studied quantitatively by finding G values with the help of absorption measur ements and calibration plots. Absorption measurements are made on solu tions of irradiated powders after being dissolved in distilled water. G-value or Radiation chemical yield is the fundamental quantitative ch aracteristic of radiation induced chemical change and it is defined as number of ions, free radicals, atoms or molecules formed or destroyed when the system has absorbed 100 eV of energy. G(I2) {Rate of formati on of free I2, molecules} for anion doped KI powder [KI: Cl, KI:Br] is more compared to pure KI powder. G(I2) for cation doped KI powder [KI :Rb, KI:Cs, KI:Na] is less compared to pure KI powder. Comparatively, G(I2) values obtained are small in KI:RbCl, KI:RbBr and KI:NaCl where both cation and anion are different from the host. These results are e xplained on the basis of misfit between impurity ions and host ions (d ifference between ionic radii of impurity ions and host ions). As misf it increases, G(I2) increases in cation doped powders where as in anio n doped powders, G(I2) increases with the decrease in misfit.