Physical stage of radiolysis

As we have already discussed in Section VIII, at the physical stage of radiolysis the primary active particles (ions, excited molecules, and electrons) are localized in separate microregions—in the track structures. The dimensions of track structures, the concentration of active particles in them, and the subsequent transformations of these particles depend on the density of the medium. 

A survey is given of the theory of the physical stage of radiolysis. Using the optical approximation to cross sections for the interaction between fast electrons and molecules, expressions have been derived for the yield g° of primary optical activations, and for the total absorbed energy Qtot It is shown that the total yield g of primary activations is conveniently discussed as a sum g° + gs, where the first term includes the action of fast electrons, while g8 describes the action of slow electrons (kinetic energy less than about 100 e.v.) on molecules of the medium. This approach is compared with Platzmans considerations on primary yields and the differences are pointed out. Finally, theoretical results of the present approach are applied to the analysis of the initial structure of the track of a fast electron, consisting of spurs, blobs, and short tracks. 

The most characteristic type of primary activations are the electronic transitions of molecules which are much faster than other response of the irradiated medium. This enables one to consider separately the physical stage of radiolysis, at the end of which a certain ensemble of excited and ionized molecules is formed in the medium. Each of the activated molecules possesses a particular amount of energy available for subsequent processes. The initial distribution and yields of individual primary activations are dealt with by the theory of primary radiation chemical yield (PRCY). We have studied the application of this theory to the radiolysis of gases in detail during the last years (16, 17, 18, 19, 20). Thus, in the formal expression—see (5), for the yield G(X) = %ngncompetitive reaction ways and remain much more obscure at the present. 

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