Samuel-Magee model

In summary, the Samuel-Magee model of low-LET tracks consists of isolated spherical spurs distributed exponentially in energy. No distinction is made between primary and secondary tracks inherent slowing down of the particle is also ignored. 

The Samuel-Magee model can be extended to a-particle tracks, considered as cylindrical columns formed by excessive spur overlap due to high LET. To a good approximation, the length I of the cylinder remains constant while its radius grows by diffusion. In this geometry, the normalized radical distribution is given by... 

The numerical and approximate analytical treatments using the Samuel-Magee model and an intercomparison of the results have been presented in an excellent review of diffusion kinetics by Kuppermann (19). He has pointed out that there is a quantitative inconsistency between the model and experiment although the agreement can be... 

The applicability of homogeneous kinetics is attributed to first-order disappearance of H20, excited water, as the rate-determining step for H2 formation, instead of the combination of reducing species as commonly assumed when using the Samuel-Magee model. Two alternative physical models of H20 are proposed. In one, H20 is the HsO + OH radical pair which is assumed to undergo geminate recombination with... 

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. 

Samuel and Magee (1953) employed a 1-radical model to find the relative forward yield in water radiolysis as a function of radiation quality. In such models, no distinction is made between reactive radicals or molecular products. The products of radiolysis are called forward (F) to denote observable molecular yield or radical (R), denoting yield of scavenger reaction at small concentration. The aim of the theory is to calculate the relative forward yield G(F)/[G(F) + G(R)], where the G values refer to the respective yields for 100 eV energy absorbed in... 

In early models (Samuel and Magee [12]), only glancing collisions were considered. Bethe [13] has shown that for non-relativistic electrons, the differential cross-section for glancing collisions is given by... 

The string of beads model has been proposed by Samuel and Magee [12] and has been widely used for the discussion of diffusion-controlled reactions in water. Radicals are supposed to be formed in spherical volumes called spurs . About 40 eV energy is deposited in each spur which are equidistant. The distance between spurs is about 3000 A for a 450 eV electron in water. The initial spur radius is 10—15 A. The picture of an electron track according to this model is given in Fig. 4(a). 

The diffusion model drawn up by Samuel and Magee (59) and later modified in the light of the knowledge that the reducing radical is a hydrated electron rather than a H atom, tried to explain the yield of all entities in the following manner (53, 54, 55, 63). 

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