Energy transfer in the gamma radiolysis of alkali and alkaline earth metal nitrates dispersed in sulphate and carbonate matrices

Gamma radiolysis of NaNO3, KNO3, Sr(NO3)2 and Ba(NO3)2 dispersed in sulphate and carbonate matrices has been studied over a wide absorbed dose range. Radiolytic decomposition of the nitrate salt depends on the concentration of the nitrate in admixture as well as the total absorbed dose. G(NO2-) values calculated on the basis of electron fraction of the nitrate salt decrease with the increase in the mol% of the nitrate salt. Percent decomposition of Na and K nitrates in sulphate and carbonate admixtures increases with the absorbed dose over a wide concentration range. An admixture of Sr(NO3)2(5 mol.%) with SrSO4 and SrCO3 exhibited an increase of G(NO2-) by 30 and 20-fold respectively. An enhancement of G(NO2-) by 25-fold has been observed in case of (5 mol.%) Sr(NO3)2 + BaSO4 admixture. G(NO2-) values for Ba(NO3)2 admixtures with BaSO4, BaCO3 and SRSO4 have been found to be much larger (16-fold) than that for the pure salt. The additives seem to exhibit sensitizing effect causing enhanced decomposition by the energy transfer process in solid state. A plausible mechanism of energy transfer involving the radical species has been proposed. EPR studies suggest the formation of radicals such as SO4-, SO3-, SO2-, NO32-, NO2 on γ-irradiation. Thermoluminescence (TL) and reflectance spectral studies indicate the possible interaction of defect centres in the matrix with NO3- causing enhanced decomposition. The efficiency of energy transfer seems to depend on the nature of the matrix, concentration of nitrate in the admixture and the absorbed dose. (author)