Radiation-chemical yield

Nearly all computations of radiation-chemical yields use either diffusion kinetics (see, e.g., Schwarz, 1969) or stochastic kinetics (Zaider et ah, 1983 Clifford et al, 1987 Pimblott, 1988 Paretzke et ah, 1991 Pimblott et ah, 1991). Diffusion kinetics uses deterministic rate laws and considers the reactions to be (partially) diffusion controlled while the reactants are also diffusing... 

Ion-molecule reactions involve a positive ion and a neutral molecule, frequently the parent molecule. Historically, there has been a dichotomy in the interpretation of the radiation-chemical yields in hydrocarbon gases. Early work by Lind (1961) and by Mund (1956) indicated the involvement of ion clustering, exemplified in the radiation-induced polymerization of acetylene as follows ... 

Notwithstanding Platzman s theory, most calculations of radiation-chemical yields in water and aqueous solutions were performed using the free-radical model (see Magee, 1953 Samuel and Magee, 1953 Ganguly and Magee, 1956). The hypothesis was that the recapture time of the electron would be shorter than the dielectric relaxation time. Therefore, recombination would outcompete solvation. 

Spur Theory of Radiation Chemical Yields Diffusion and Stochastic Models... 

In neutral water the radiation chemical yields G are 2.7 x 10 7 mol J-1 for the hydrated electron, 2.8 x ] 0 7 mol, 1 1 for the "OH radical and 6 x 10 x mol J-1 for the H atom. These values vary slightly with the solute concentration, due to increased reaction with the solute in the radiation spurs. In order to study the reaction of one radical without interference of the others, scavengers have to be added to the system. The best scavengers are those which will convert the unwanted radical to the studied one. This can be done with eaq, which can be converted to "OH or to H by the addition of N2O or H+, respectively (equations 3 and 4). 

Changes in the properties of polymer materials caused by absorption of high-energy radiation result from a variety of chemical reactions subsequent to the initial ionization and excitation. A number of experimental procedures may be used to measure, directly or indirectly, the radiation chemical yields for these reactions. The chemical structure of the polymer molecule is the main determinant of the nature and extent of the radiation degradation, but there are many other parameters which influence the behaviour of any polymer material when subjected to high-energy radiation. 

Radiation chemical yields are conventionally expressed in G values for numbers of molecules changed or formed for 16 aJ (100 eV) of energy absorbed. 

There is a large amount of experimental data on the radiation chemical yield of Caq, including direct absorption measurements of the time dependence of the yield in deaerated... 

According to the optical approximation, which was shown by Platzman [4] to be based on the Born-Bethe theory, a radiation chemical yield of channel G, may be estimated from optical data as shown in the following equation ... 

In this chapter, the various radiation chemical yields, known as G-values, are defined as follows g(X) is the yield of the species in reactions (6) and (7) G°(X) is the yield of the initial products of water radiolysis at the end of the physicochemical stage and G(X) is an experimentally measured yield. In some publications Gx, rather than g(X), is used to represent the primary yield of the species X. The yields in reactions (6) and (7) are numerically very similar, but one must be sure of the units that are being used to express them. In the older literature, it was common practice to quote G-values without units when the units were in fact molecules (100 eV) ... 

Experimental approaches to measure the radial dose distribution are also in progress [119], and it was found that the distribution follows r law in the inner region of a critical distance and obeys r law outside of that region. LaVerne and Schuler reported the considerable decrease in the radiation chemical yield for ferric production in the Fricke dosimeter, suggesting a model of a deposited energy density in an ion track, which depends on the LET and the atomic number of an irradiation particle [120,121]. 

Figure 5 Relation between the radiation chemical yield of the benzyl radical and the concentration of benzyl esters in 2-methyltetrahydrofuran and toluene at 77 K.

A Novel Technique for Determining Radiation Chemical Yields of Negative Electron-Beam Resists... 

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