Water radiolysis major products

Carbon dioxide is the major product of the radiolysis, and results from the loss of the carboxyl group. Carbon monoxide is found in somewhat smaller yield than carbon dioxide. Vater is also produced, but its yield is often difficult to quantify because of the strong hydrogen bonding which exists between water and carboxylic acid groups. Hydrogen is not normally found in high yield. 

The discussion in the previous section suggests that the track of a heavy ion becomes more like that of a fast electron with increasing velocity. Therefore one expects that in the high velocity limit the yields of water products with heavy ions are the same as with fast electrons or y-rays. The yields for the major products of water radiolysis in fast electron or y-radiolysis are given in Table 1. These values were taken from a number of different sources in conjunction with the results predicted by model calculations [73,116,119-123]. Material balance shows that almost four molecules of water are decomposed for every 100 eV of energy absorbed by fast electrons or y-rays. Because only about six water molecules are initially decomposed, most of the water products escape intraspur reactions in fast electron or y-radiolysis. 

The hydrated electron, if the major reducing species in water. A number of its properties are important either in understanding or measuring its kinetic behavior in radiolysis. Such properties are the molar extinction coefficient, the charge, the equilibrium constant for interconversion with H atoms, the hydration energy, the redox potential, the reaction radius, and the diffusion constant. Measured or estimated values for these quantities can be found in the literature. The rate constants for the reaction of Bag with other products of water radiolysis are in many cases diffusion controlled. These rate constants for reactions between the transient species in aqueous radiolysis are essential for testing the "diffusion from spurs" model of aqueous radiation chemistry. 

A word of caution is needed at this point the radiolytic yields employed in radioly-sis modeling should be the primary yields corresponding to events that occur within the time of scission of a bond within a water molecule. These values are impossible to measure, because no techniques are available for sampling the concentrations of primary radiolysis products in the sub-femtosecond time frame. Thus, the radiolytic yields that are used to devise water radiolysis models are strictly not the values that are appropriate or needed. However, as with many physicochemical models, values for various parameters are often selected so that the original observations are reproduced. A major problem in radiolysis modeling is that there are many more parameters than there are experimental observations, so the values assigned to the models are not unique and they should not be transferred from model to model. Nevertheless, the models have proved to be quite robust, in the sense that reasonable... 

Key water chemistry issues have been identified by Guzonas et al. (2012) predicting and controlling water radiolysis and corrosion product transport (including fission products) remain the major R D areas. In this regard, the operating experience using nuclear steam reheat at the Beloyarsk nuclear power plant (NPP) in Russia is extremely valuable. 

Examination of such degraded solvents is difficult from the analytical point of view. In multicomponent extractant-diluent/aqueous phase systems, free radicals are produced by radiolysis of major compounds water, acid, extractant, and diluent. These radicals, after dimerization or coupling with other compounds, are responsible for the formation of several families of compounds. For instance, in the PUREX process, the exposure of the solvent to radiolysis gives rise to a mixture of over 200 secondary products, most of them in trace quantities. 

The production of H2 in the radiolysis of water has been extensively re-examined in recent years [8], Previous studies had assumed that the main mechanism for H2 production was due to radical reactions of the hydrated electron and H atoms. Selected scavenger studies have shown that the precursor to the hydrated electron is also the precursor to H2. The majority of H2 production in the track of heavy ions is due to dissociative combination reactions between the precursor to the hydrated electron and the molecular water cation. Dissociative electron attachment reactions may also play some role in y-ray and fast electron radiolysis. The radiation chemical yield, G-value, of H2 is 0.45 molecule/100 eV at about 1 microsecond in the radiolysis of water with y-rays. This value may be different in the radiolysis of adsorbed water because of its dissociation at the surface, steric effects, or transport of energy through the interface. 

The technique has been described in detail elsewhere. [26] In short, a pulse of high energy electrons induces a series of chemical reactions that can be monitored, e.g., using time resolved UV-vis spectroscopy. The reaction of interest is usually induced by a reaction between a radical formed from radiolysis of the solvent (usually water) and a solute molecule. The primary radiolysis products in aqueous solution are HO, e q", H, HjOj, H2 and The major radical species, HO and e q, are formed in equimolar concentrations, 0.28 ol/J each, on electron or y-irradiation.[27] As can be seen in reaction 2, the hydroxyl radical does not yield a benzene radical cation instantly upon reaction with a substituted benzene. For this reason, secondary oxidants, such as S04, Brj and N3, are usually used to generate benzene radical cations. To determine one-electron reduction potentials of radical cations, the redox equilibrium between the radical cation of interest and a redox couple with a known one-electron reduction potential is studied. The equilibrium constant can be derived from the rate constants of the electron-transfer reaction and the back reaction and/or the equilibrium concentrations of the two redox couples (reaction 6).[28]... 

Comparative studies are indeed effected especially for aqueous solutions. However, many important differences exist, and the existence of hydrated electrons in the products of water sonolysis are still controversial. In addition, many sonolyses occur primarily in the gas phase of the bubble, while radiolytic reactions occur in the solution. A major limitation, of importance for synthetic chemists, is that little is known concerning the basic aspects of cavitation in organic media, but the situation is still worse concerning their behavior under radiolysis. 

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