Kinetics of the radiation induced

Isotopic Exchange Reactions. Exchange reactions between the isotopes of hydrogen are well known and well substantiated. The equihbrium constants for exchange between the various hydrogen molecular species have been documented (18). Kinetics of the radiation-induced exchange reactions of hydrogen, deuterium, and tritium have been critically and authoritatively reviewed (31). The reaction T2 + H2 — 2HT equiUbrates at room temperature even without a catalyst (30). 

J. W. Pyper and C. K. Briggs, Kinetics of the Radiation-induced Exchange Reactions of Hydrogen, Deuterium, and Tritium, Eawrence Eipermore Eaboratory Report... 

The effects of minute traces of water on the kinetics of the radiation-induced polymerization of a-methylstyrene have been known and studied for some time by several workers (2, 3, 10, 16). Although these studies have shed much light on the subject, all have been handicapped by irreproducibility in the data from sample to sample. Williams (3) was the first to use dilatometers to eliminate some of the effects of irreproducibility, but even then a wide range in polymerization rates on different dilatometers was obtained. Perhaps then, one of the most sig-... 

Recently, Garreau et al. (1979) reported a careful and rather detailed study of the kinetics of the radiation-induced polymerization of styrene in emulsion with sodium lauryl sulfate under conditions found earlier to lend to close agreement with simple Case 2 Smilh-Ewart kinetics (Smith, 1948). Most of the normal reaction variables were studied, and the rates of polymerization were found to be independent of the luonomer-to-water... 

Kinetics of the Radiation Induced Isotopic Exchange between Iodobenzene and Iodine... 

Effects of dose rate on the concentration of free radicals were examined by performing the test at 163 kGy dose with a dose rate of 1 kGy/h, and the results are shown in Figure 25.25(a). Concentration of free radicals decreases with increasing dose rate, i.e. the lower dose rate produced higher concentration of radicals. Decay kinetics of the radiation-induced carbon black free radicals were measured by taking ESR of samples at an interval of 3-5 min after withdrawal of the radiation source. Figure 25.25(b) shows the measured decay... 

The irradiation of water is immediately followed by a period of fast chemistry, whose short-time kinetics reflects the competition between the relaxation of the nonhomogeneous spatial distributions of the radiation-induced reactants and their reactions. A variety of gamma and energetic electron experiments are available in the literature. Stochastic simulation methods have been used to model the observed short-time radiation chemical kinetics of water and the radiation chemistry of aqueous solutions of scavengers for the hydrated electron and the hydroxyl radical to provide fundamental information for use in the elucidation of more complex, complicated chemical, and biological systems found in real-world scenarios. 

Of special interest in the recent years was the kinetics of defect radiation-induced aggregation in a form of colloids-, in alkali halides MeX irradiated at high temperatures and high doses bubbles filled with X2 gas and metal particles with several nanometers in size were observed [58] more than once. Several theoretical formalisms were developed for describing this phenomenon, which could be classified as three general categories (i) macroscopic theory [59-62], which is based on the rate equations for macroscopic defect concentrations (ii) mesoscopic theory [63-65] operating with space-dependent local concentrations of point defects, and lastly (iii) discussed in Section 7.1 microscopic theory based on the hierarchy of equations for many-particle densities (in principle, it is infinite and contains complete information about all kinds of spatial correlation within different clusters of defects). 

Pulse radiolysis studies concerning the polymerization as well as the degradation, crosslinking and radiation resistance of polymers are surveyed. Initiation mechanisms of the radiation-induced polymerization of styrene and other monomers are discussed on the basis of the direct measurements of the reaction intermediates. Optical and kinetic data on the short-lived chemical intermediates produced in the solution of polymers and in the rigid polymers are surveyed and discussed with special reference to the degradation mechanism of polymers. 

There is a large amount of data on nonhomogeneous track chemistry of energetic electrons at room temperature, and the track structure and diffusion-limited kinetics are well parameterized. This wealth of knowledge contrasts with the limited information about the effects of radiation on aqueous solutions at elevated temperatures. The majority of the studies at elevated temperatures have been performed at AECL, Canada [93], or at the Cookridge Radiation Laboratory, University of Leeds, UK [94]. These two groups have focused on measuring the rate coefficients of the reactions of the radiation-induced radicals and ions of water. The majority of the temperature dependencies can be fitted with an empirical Arrhenius-type expression, k = A This type of parameterization provides a... 

The experimental and theoretical aspects of the radiation and self-induced conversion kinetics and equiUbria between the ortho and para forms of hydrogen, deuterium, and tritium have been correlated (17). In general, the radiation-induced transitions are faster than the self-induced transitions. 

In addition to the generation of platelets, hydrogenation of silicon also induces electronic deep levels in the band gap. As in the case of platelet formation, these defects are considered to be unrelated to either plasma or radiation damage because they can be introduced with a remote hydrogen plasma. Comparison of depth distributions and annealing kinetics of the platelets and gap states has been used to a limited extent to probe the relationship among these manifestations of H-induced defects. 

The possible formation of an alloyed or a core-shell cluster depends on the kinetic competition between, on one hand, the irreversible release of the metal ions displaced by the excess ions of the more noble metal after electron transfer and, on the other hand, the radiation-induced reduction of both metal ions, which depends on the dose rate (Table 5). The pulse radiolysis study of a mixed system [66] (Fig. 7) suggested that a very fast and total reduction by the means of a powerful and sudden irradiation delivered for instance by an electron beam (EB) should prevent the intermetal electron transfer and produce alloyed clusters. Indeed, such a decisive effect of the dose rate has been demonstrated [102]. However, the competition imposed by the metal displacement is more or less serious, because, depending on the couple of metals, the process may not occur [53], or, on the contrary, may last only hours, minutes, or even seconds [102]. 

A seemingly similar process of polymerization - the radiation induced polymerization of methyl acrylate in n-hexane - shows also auto-acceleration and post-polymerization. Polymerization was carried out under precipitating conditions. Using the results of kinetics examination, the authors showed that all effects can be explained by the mechanism based on trapped radical reactions in particles of precipitated polymer. No influence of any template effect was detected in these systems. 

Radiation-induced polymerization of crystalline tetroxocane gives a highly crystalline linear polymer in essentially 100% yield (63MI51900,68MI51901), and this has attracted some industrial attention. Tetroxocane also gives a crystalline polymer very rapidly under cationic conditions (boron trifluoride etherate catalyst) and the kinetics of the process have been studied <76MI51900>. 

The most important feature of ionizing radiations is, as the term implies, ionization to give ionic intermediates in irradiated systems. Though radiation-induced radical polymerization had long been studied, it is only a decade since radiation-induced ionic polymerization was first found. In 1957, Davison et al. obtained polymer from isobutene, which is known not to be polymerized by radical catalysts, by irradiating at low temperature with y-rays (7). Before long, the radiation-induced polymerization of styrene was proved to proceed as an ionic mechanism in suitable solvents (2,3,4). Since these pioneering researches, the study of the chemical kinetics of radiation-induced ionic polymerization has been extended to several vinyl, diene and cyclic monomers. 

The authors of this book started working on chemical kinetics more than 10 years ago focusing on investigations of particular radiation - induced processes in solids and liquids. Condensed matter physics, however, treats point (radiation) defects as active particles whose individual characteristics define kinetics of possible processes and radiation properties of materials. A study of an ensemble of such particles (defects), especially if they are created in large concentrations under irradiation for a long time, has lead us to many-particle problems, common in statistical physics. However, the standard theory of diffusion-controlled reactions as developed by Smoluchowski... 

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