Post-irradiation reduction

Post-irradiation reduction of cerium(IV) occurs when concentrated sodium nitrate solutions in air-saturated 0.4M sulfuric acid containing 10 4M cerium(IV) are irradiated with a kilocurie G0Co source. A kinetic study of the reaction of cerium(IV) with nitrous acid established that the postirradiation reaction is reduction of cerium(IV) by nitrous acid. A computer program SLOPULSE was used to determine G(HNO>) by kinetic analyses of both the post-irradiation reduction of cerium(IV) and reduction of cerium(IV) by nitrous acid during irradiation. The importance of nitrous acid as an intermediate is evidenced by the high values for G(HN02)- For example, about 70% of the reduction of cerium(IV) in 5.0M sodium nitrate solutions is caused by nitrous acid with G(CeIU) = 6.04 and G(HNG2) = 2.22. 

This paper establishes the importance of nitrous acid as a transient intermediate in the reduction of cerium (IV). Post-irradiation reduction of cerium (IV) is conveniently observable when concentrated sodium nitrate solutions in 0.4AI sulfuric acid containing about 10"4M cerium (IV) are irradiated with a kilocurie 60Co source. This paper presents kinetic evidence that the post-irradiation reaction is reduction of cerium (IV) by nitrous acid and reports the dependence of G(HN02) on sodium nitrate concentration. 

Typical experimental data which demonstrate the post-irradiation reduction of cerium (IV) are shown in Figure 2. After an irradiation... 

Figure 2. Post-irradiation reduction of cerium(IV) after 60Co gamma radiolysis of air saturated 0.8N sulfuric acid containing 3.0M sodium nitrate and 10 M cerium(IV) in a 2 cm. cell. Irradiation time was 30.2 sec. Optical densities at 340 m were 1.970 initially, 1.029 after post-irradiation reaction was sensibly complete and 0.855 owing to absorption by 0.8N sulfuric acid containing 3.0M sodium nitrate...

Figure 5. Kinetic evidence that the post-irradiation reduction of cerium(IV) is thermal reduction of ce-rium(IV) by nitrous acid Thermal reduction of cerium(IV) O Post-irradiation reduction of cerium(IV)...

Post-irradiation reduction of cerium (IV) in concentrated sodium nitrate solutions was previously reported by Pikaev, Glazunov, and Yakubovich (20) in pulsed electron irradiations of 0.8IV sulfuric acid containing 0.5M sodium nitrate and 2 X 10"4M cerium (IV). They attributed the post-irradiation reaction to intermediate formation of pernitric acid, originally suggested by Allen (1) as an intermediate in the radiolysis of nitric acid solutions. Furthermore, they ruled out nitrous acid since it has been shown previously that the non-radiolytic reaction between cerium (IV) and nitrous acid goes to completion very quickly under the same conditions. However, they presented no evidence to refute the... 

Since we have obtained evidence for nitrous acid as the intermediate which causes post-irradiation reduction of cerium (IV) for 00Co gamma experiments, nitrous acid must also be the intermediate which causes the post-irradiation reaction in the pulsed electron experiments of Pikaev, Glazunov, and Yakubovich (20). Their failure to reach this conclusion may be because of non-uniform energy absorption which caused cerium-(IV) concentration gradients in their irradiated solutions and made difficult the duplication of identical conditions for the non-radiolytic reaction between cerium (IV) and nitrous acid. Energy absorption in the Ghorm-ley-Hochanadel (9) source, which we used, is essentially uniform. 

Aqueous plutonium photochemistry is briefly reviewed. Photochemical reactions of plutonium in several acid media have been indicated, and detailed information for such reactions has been reported for perchlorate systems. Photochemical reductions of Pu(VI) to Pu(V) and Pu(IV) to Pu(III) are discussed and are compared to the U(VI)/(V) and Ce(IV)/(III) systems respectively. The reversible photoshift in the Pu(IV) disproportionation reaction is highlighted, and the unique features of this reaction are stressed. The results for photoenhancement of Pu(IV) polymer degradation are presented and an explanation of the post-irradiation effect is offered. 

The consequences of post-irradiation effects in polymer materials are progressive reduction in strength, cracking and embrittlement. Some reduction in these effects can be achieved by annealing of the trapped radicals, addition of appropriate... 

Reduction of Cerium(IV) by Nitrous Acid Reaction Kinetics. Since the effect of nitrate ion on G(Cem) was previously attributed (23) to intermediate formation of nitrite ion, the thermal reduction of cerium (IV) by nitrous acid was investigated with reactant concentrations comparable with those encountered in the post-irradiation reaction. We discovered that the reduction of cerium (IV) by nitrous acid was slow, with reaction rates comparable with those rates observed in post-irradiation reactions. Typical experimental data are shown in Figure 3. About 5 seconds were required to prepare the mixture before the optical density could be recorded as a function of time after mixing. 

Field and his associates prepared a variety of novel disulfides and observed "good" protection in mice with 2-acetamidoethyl acetyl disul-fide (< 50 mg/kg), with p-cyanobenzyl 2-(n-decylamino)ethyl disulfide (p-CHo, p-CHO and p-Cl analogs were Inactive) and with. 3-acetamidopropyl 2-(n-decylamino)ethyl disulfide l (30-50 mg/kg). The 2-acetamido isomer of the last-named compound was much less protective. Thiamine tetrahydro-furfuryl disulfide (40 mg/kg, i.p., post-irradiation) protected mice against 600-700r with a dose reduction factor of 1.34. ... 

A dose reduction factor of 3,8 in mice was achieved by combining a variety of drugs and factors.These included MEA (200 mg/kg, 15 min. pre-irradiation), hypoxia (nitrogen atmosphere during irradiation), syngeneic bone marrow (22 hrs. post-irradiation), sodium penicillin G (50,000 I. U., 30 days) and streptomycin (50 mg/kg, 30 days). 

Hi. Lysine. Gamma radiolysis of aerated aqueous solution of lysine (94) has been shown, as inferred from iodometric measurements, to give rise to hydroperoxides in a similar yield to that observed for valine and leucine. However, attempts to isolate by HPLC the peroxidic derivatives using the post-column derivatization chemiluminescence detection approach were unsuccessful. This was assumed to be due to the instability of the lysine hydroperoxides under the conditions of HPLC analysis. Indirect evidence for the OH-mediated formation of hydroperoxides was provided by the isolation of four hydroxylated derivatives of lysine as 9-fluoromethyl chloroformate (FMOC) derivatives . Interestingly, NaBILj reduction of the irradiated lysine solutions before FMOC derivatization is accompanied by a notable increase in the yields of hydroxylysine isomers. Among the latter oxidized compounds, 3-hydroxy lysine was characterized by extensive H NMR and ESI-MS measurements whereas one diastereomer of 4-hydroxylysine and the two isomeric forms of 5-hydroxylysine were identified by comparison of their HPLC features as FMOC derivatives with those of authentic samples prepared by chemical synthesis. A reasonable mechanism for the formation of the four different hydroxylysines and, therefore, of related hydroperoxides 98-100, involves initial OH-mediated hydrogen abstraction followed by O2 addition to the carbon-centered radicals 95-97 thus formed and subsequent reduction of the resulting peroxyl radicals (equation 55). 

After 21 hours of irradiation the concrete was again sampled in close proximity to pretreatment samples (Figure 4). Post-treatment Aroclor 1260 levels were 43 + 13 ug/100 cm (n = 8). The 47 reduction in PCB concentration is statistically significant at the 99% confidence level. 

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