Transformation mechanisms between solid material and ion in solutions by radiolysis and sonolysis

Radiolytic and sonolytic redox reactions of technetium that was one of long-lived fission products formed in the nuclear materials were investigated.An aqueous solution of pertechnetate(Tc(VII)O_4)that was the most stable chemical species under oxidative conditions was irradiated with bremsstrahlung produced by an electron linear accelerator，and the formation of nanoparticles of technetium(IV)oxide hydrate(Tc(IV)O_2·nH_2O)was confirmed.This reaction was triggered by a bimolecular reaction of Tc(VII)and hydrated electrons produced by radiolysis of water molecules。The mechanisms of the reducing processes involving disproportionation reactions of Tc(VI)and Tc(V)were clarified.Aqueous pertechnetate(Tc(VII)O_4)solutions and Tc(IV)O_2-nH_2O colloids solutions([Tc]=0.1 mM)were sonicated(200 kHz，200W)in a glass cell with flat bottom under Ar or He atmosphere at 20℃。No reduction of TcO_4was observed in this study.However，it was observed that TcO_2·nH_2O colloids dispersed in an aqueous solution were completely dissolved by ultrasonic treatment within30min under Ar atmosphere，and TcO_4was eventually produced.The production of TcO_4was considerably suppressed in the presence of t-butyl alcohol(An Effective Scavenger Of OH Radicals)，indicating that Tc(IV)was oxidized by OH radicals(Produced By Dissociation Of Water Molecules)in hot cavitation bubbles created by ultrasound。The formation rate of TcO_4under.He atmosphere was slower than that under Ar atmosphere.This can be attributed to a difference of the effective maximum temperature in the collapsing bubbles。Because thermal conductivity of He is much higher than Ar，thermal transport effectively occurs from the bubbles to the surrounding liquid.Thus，temperature of cavitation bubbles filled with He should be lower than those filled with Ar，resulting in the slower OH formation rate。

Radiolytic and sonolytic redox reactions of technetium that was one of long-lived fission products formed in the nuclear materials were investigated. An aqueous solution of pertechnetate (Tc(VII)O_4) that was the most stable chemical species under oxidative conditions was irradiated with bremsstrahlung produced by an electron linear accelerator, and the formation of nanoparticles of technetium(IV) oxide hydrate (Tc(IV)O_2・nH_2O ) was confirmed. This reaction was triggered by a bimolecular reaction of Tc(VII)and hydrated electrons produced by radiolysis of water molecules. The mechanisms of the reducing processes involving disproportionation reactions of Tc(VI) and Tc(V) were clarified.Aqueous pertechnetate (Tc(VII)O_4) solutions and Tc(IV)O_2-nH_2O colloids solutions ([Tc] = 0.1 mM)were sonicated (200 kHz, 200 W) in a glass cell with flat bottom under Ar or He atmosphere at 20℃. No reduction of TcO_4 was observed in this study. However, it was observed that TcO_2・nH_2O colloids dispersed in an aqueous solution were completely dissolved by ultrasonic treatment within 30 min under Ar atmosphere, and TcO_4 was eventually produced. The production of TcO_4 was considerably suppressed in the presence of t-butyl alcohol (an effective scavenger of OH radicals), indicating that Tc(IV) was oxidized by OH radicals (produced by dissociation of water molecules) in hot cavitation bubbles created by ultrasound. The formation rate of TcO_4 under. He atmosphere was slower than that under Ar atmosphere. This can be attributed to a difference of the effective maximum temperature in the collapsing bubbles. Because thermal conductivity of He is much higher than Ar, thermal transport effectively occurs from the bubbles to the surrounding liquid. Thus, temperature of cavitation bubbles filled with He should be lower than those filled with Ar, resulting in the slower OH formation rate.