Effect of sulfate additives on the 60Co gamma ray induced decomposition of lanthanum,europium and terbium nitrates in solid state

Gamma radiolysis of binary mixtures of La(NO₃)₃·6H₂O, Eu(NO₃)₃·6H₂O and Tb(NO₃)₃·6H₂O along with their respective sulfates have been studied over a wide range of absorbed doses up to 500 kGy. Radiolytic decomposition of the nitrate salts is affected by the concentration of the sulfate in the binary mixture as well as on the absorbed dose. G(NO₂⁻) values calculated on the basis of electron fraction of the nitrate salt in the binary mixture are enhanced by 10²–10³ times at >90 mol% of the sulfate additive. A study of binary mixtures of lanthanum nitrate with other mono-, bi-, tri- and tetra-valent sulfate additives shows that G(NO₂⁻) values are also affected by the nature and oxidation state of the cation including electron configuration. ESR and TL measurements suggest the formation of radical species, which may interact with the radical species of nitrate (NO₃²⁻, NO₂ etc.) causing enhanced decomposition by energy transfer. A possible mechanism of decomposition has been suggested. Anomalous behavior of Eu(NO₃)₃·6H₂O has been correlated with the electronic configuration and +2 oxidation state of Eu.