EFFECT OF NO_3~- AND NO_2~- ON WATER RADIOLYSIS KINETICS DURING γ- IRRADIATION

摘要

The effects of NO_3~- and NO_2~- on the continuous γ-radiolysis of water were studied at an absorbed dose rate of 2.1 Gy·s~(-1) at room temperature. Air- or argon-saturated nitrate or nitrite solutions at pH 6.0 and 10.6 were irradiated and the aqueous concentrations of molecular radiolysis products, H_2 and H_2O_2, and the variation in the concentration of NO_3~- and NO_2~- were measured as a function of irradiation time. Computer simulations using a comprehensive radiolysis kinetic model were also performed to aid in interpretation of the experimental results. The impact of nitrate and nitrite present at concentrations below 10~(-3) M on water radiolysis processes occurs mainly through reactions with the radical species generated by water radiolysis, •e_(aq)~-, •O_2~- and •OH. The changes in H_2 and H_2O_2 concentrations observed in the presence of nitrate and nitrite under a variety of conditions can be explained by the reduction in the radical concentrations. The kinetic analysis shows that the main loss pathway for H_2 is the reaction with •OH and the loss pathways for H_2O_2 are reactions with •e_(aq)~- and •OH. This relationship holds even in the presence of impurities such as nitrate and nitrite. Hence post-irradiation measurements of H_2, H_2O_2 and NO_2~-/NO_3~- can be used to calculate radical concentrations and provide information on the redox conditions of the irradiated aqueous solutions.