Radiolytic Process

Polyphosphazene films could also be modified very easily by grafting organic polymers onto the surface using chemical, photochemical or y-radiolytic processes. In almost all cases these studies led to the increase in the surface hy-drophilicity and biocompatibility of the phosphazene films without depressing their bulk features. 

Methyl-Cobalamine and Related Compounds. There are three major types of cobalamine in animals and man, the methyl and hydroxo derivatives and the deoxyadenosyl derivative (coenzyme B12). The unique metal-carbon bond in the methyl derivative and in B12 is extremely photolabile, and their photolyses have been widely studied. However, radiolytic processes have not been widely studied. 

The transient absorption spectrum assigned to 9 and intramolecular rr-dimer" of 9 was observed immediately after 8-nsec e , and decayed with the formation of new peaks at 480 and 520 nm assigned to Np"2 (Fig. 6). This indicates that intramolecular dimerization in 9 occurs to reversibly form TV-dimeratk = 1.0 x 10 -1.0 x 10 sec In DCE, 9 and rr-dimer disappeared by neutralization with Cl generated by the initial radiolytic processes at = 4.7 x 10 ° sec From the time profile of the transient absorption at 520 nm involving the formation of Np"2 and decay of tt-dimer" of 9" k, = 5.3 x 10 sec is estimated for the reaction. 

In fact, the rate of formation of the carbonium ions from the 8-decay is simply proportional to the first power of the concentration of the tritiated compound in the system. On the other hand, the rate of formation of labeled radiolytic products varies with a higher power of the concentration of tritiated molecules which determines, in the first place, the intensity of the 3-radiation (and therefore the total rate of the radiolytic reactions), and in the second place, the probability that the radiolytic processes affect, in particular, a tritiated molecule. 

The experimental procedures were adapted to allow the application of a number of physical and chemical techniques, including the use of radical scavengers, ionic interceptors, deuteriated reagents, pressure-dependence studies, competition kinetics, etc. A serious problem, already encountered in the study of the carbonium ions directly formed from the decay of tritiated hydrocarbons (vide supra), arises from the possibility that radiolytic processes, promoted by the j8-radiation of... 

Bruno J, Cera E, Grive M, Eklund U-B, Eriksen T. (1999) Experimental determination and chemical modelling of radiolytic processes at the spent fuel/water interface. Swedish Nuclear Euel and Waste Management Co, TR-99-26. 

Note that solvated electrons can also be produced by photodetachment of electrons from certain anions or photoionization of molecules using UV excitation.Then the mechanism of metal ion reduction is expected to be quite similar to the radiolytic processes of Figures 2a, 2b and 2c. However, the matrices used as cluster hosts are generally not transparent to light, and the reduction is often restricted to the surface. 

A second example is the decomposition of methanol over zinc oxide irradiated with y-rays 120). The enhanced rate of decomposition was said to anneal out rapidly when irradiation was stopped, but the extent to which catalysis is responsible would be more certain if the decay had been measured. The value of the yield also speaks for catalysis rather than radiolysis, because it was about 4 x 10 molecules decomposed per 100 ev absorbed by the total system, an impossibly high number for a nonchain radiolytic process. Since the reaction involved is spontaneous at 400°, there is no requirement for a nonthermal source of energy. 

Although this study of the radiolysis of methane was exploratory, it illustrated the usefulness of the wide-range radiolysis source, and our results contribute to the understanding of the radiolytic process which has been so controversial. Further development of the apparatus and techniques are contemplated, and the methane system will be studied further and in more detail. 

While the generation of carotenoid radical cations was originally achieved by radiolytic processes they have now been prepared photochemically (Tinkler et al., 1996), chemically (Ding et al, 1988), and via electrochemical methods (Grant et al., 1988). In the electrochemical study both one-electron and two-electron oxidation was observed with the two-electron oxidation subsequently producing the radical cation via reactions of the type ... 

From the magnitude of the quantum efficiency and the difference in behavior between the photolysis and radiolysis, it seems unlikely that the lowest excited state plays a major role in the radiolytic processes. However, nitrate has another, much stronger (f — 0.3) absorption at 6 e.v., and we have recently obtained results which suggest that this level may be involved in the radiolysis processes (discussed below). 

Rate constants and pK values for the following radiolytic processes in aqueous p-nitrophenol solutions were obtained ... 

As a preliminary step in this inquiry into the nature of the radiolytic processes that lead to degradation of the peptide chain, we have completed a detailed study of the reaction products formed in the y-radiolysis... 

The usual extrapolation of experimental knowledge back along the time sequence of radiolytic processes has provided us with the picture of a radical track which is formed at the beginning of the chemical stage. While the further development of this track by diffusion and chemical reactions had been successfully treated in great detail by the theory of diffusion kinetics, the initial structure of the track was pictured only... 

In conclusion, it may be said that, at present, theory appears to be able to provide a useful a priori information on primary radiolytic processes and yields. 

A detailed piece of earher work was also concerned with muon end-of-track radiolytical processes in acetone [23], The muonated species observed on a microsecond time scale is the radical formed formally by Mu addition to the carbonyl oxygen. It was shown that two-thirds of the radicals were indeed formed by addition of Mu on a time scale of 0.1 ns. The remaiiting one-third did not involve a Mu precursor and was instead formed by direct combination of a track electron with a muon-acetone complex, or of a muon with an acetone anion, on a time scale of about 3 ns. This conclusion was based on an analysis of the observed initial phases of muon precession as a function of the apphed magnetic field, and it takes advantage of the ct that the muon in a diamagnetic environment precesses in the opposite direction, and with a different precession fi-equency compared with the muon in Mu. 

In radiation chemistry, the muon is an end-of-track probe that is suited to give unique information on radiolytic processes. 

Other radiolytic processes can occur in such proteins that lead to side chain scission and the formation of volatiles from specific amino acid moieties [17],... 

Radiolytic Processes Yielding Active Species for Synthesis of Nanoparticles...506... 

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