Track Effects in Radiation Chemistry

In radiation chemistry, the track effect is synonymous with LET variation of product yield. Usually, the product measured is a new molecule or a quasi-stable radical, but it can also be an electron that has escaped recombination or a photon emitted in a luminescent process. Here LET implies, by convention, the initial LET, although the actual LET varies along the particle track also, the secondary electrons frequently represent regions of heterogeneous LET against the background of the main particle. 

In theory, one assumes the formation of radicals before the chemical stage begins (see Sect. 2.2.3). These radicals interact with each other to give molecular products, or they may diffuse away to be picked up by a scavenger in a homogeneous reaction to give radical yields. The overlap of the reactive radicals is more on the track of a high-LET particle. Therefore, the molecular yields should increase and the radical yields should decrease with LET. This trend is often observed, and it lends support to the diffusion-kinetic model of radiation-chemical reactions. 

The quantitative aspects of track reactions are involved some details will be presented in Chapter 7. The LET effect is known for H2 and H202 yields in aqueous radiation chemistry. The yields of secondary reactions that depend on either the molecular or the radical yield are affected similarly. Thus, the yield of Fe3+ ion in the Fricke dosimeter system and the initiation yield of radiation-induced polymerization decrease with LET. Numerous examples of LET effects are known in radiation chemistry (Allen, 1961 Falconer and Burton, 1963 Burns and Barker, 1965) and in radiation biology (Lamerton, 1963). 

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INTERACTION OF CHARGED PARTICLES WITH MOLECULAR MEDIUM AND TRACK EFFECTS IN RADIATION CHEMISTRY... 

Schuler MA, Bhatia K, Schuler RH (1974) Radiation chemical studies on systems related to ascorbic acid. The radiolysis of aqueous solutions of a-bromotetronic acid. J Phys Chem 78 1063-1074 Schuler RH, Hartzell AL, Behar B (1981) Track effects in radiation chemistry. Concentration dependence for the scavenging of OH by ferrocyanide in NqO-saturated solutions. J Phys Chem... 

Papers328,329 by Polyansky and one of the authors contain calculations of the spectral and energy yields of VCR in tracks of electrons with energies attained in accelerators used in radiation chemistry. It is emphasized that the VCR can induce photoradiation processes in tracks of fast electrons, that is, the inner photoradiation effect. 

Samuel AH, Magee JL. (1953) Theory of radiation chemistry. 11. Track effects in radiolysis of water. J Chem Phys 21 1080-1087. 

The fundamental processes involved in the physical formation of a radiation track and in its subsequent evolution by diffusion and reaction are stochastic in nature. Every track is unique and even identical tracks may evolve differently. Thus most recent simulation methods [5-8] are stochastic in these senses (i.e. for the underlying track and for the diffusion and reaction of the reactive particles that can take place). Unfortunately, these methods ignore the spin-dynamics because of the complexity it introduces. As most radicals in radiation chemistry are paramagnetic species, there is a possibility of spin-controlled reactions and other spin effects such as quantum beats [9], chemically induced dynamic nuclear polarisation (CIDNP) [10-13] and chemically induced dynamic electron polarisation (CIDEP) [11, 12], which would... 

While most studies of radiation chemistry track effects have been carried out in condensed phase, and particularly in liquids, evidence of Pl due to interaction with track electrons or other paramagnetic species (e.g. N2 has also been seen in gases at high pressures and as well near the critical point in ethane [19]. 

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