Processes radiation-chemical

The practical utilization of radiation-chemical processes in water technology is based on the destructive and bionegative effects of a high-energy radiation on aqueous systems. 

As the sources of radiation both gamma radiation ( Co, Cs) and electron accelerators can be used. The effect of high-energy radiation on 

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The outcome of rapid radiation chemical processes in mammalian cells is to cause a variety of longer-Hved physical alterations in the DNA. Of these, double-strand breaks (DSBs) appear to be most frequently involved in cell killing if not correctly repaired. In general, thiols protect against DSB induction in proportion to their effect on cell killing (7), although there are exceptions (8). 

Radiation chemical processes involving cosmic and UV irradiation The extremely low density of material in interstellar space (ISM gas and ISM nuclei), which could affect the cometary material in the course of millions of years... 

Various industrial pilot plants and full-scale operations, using radiation-chemical processing have been reported, with production rates -50 to -1000 tons per year (Spinks and Woods, 1990 Chutny and Kucera, 1974). Production rates less than -50 tons per year are not considered viable. These operations are or have been conducted in countries such as the United States, the former U.S.S.R., Japan, and France. However, some operations have also been reported in the former Czechoslovakia and Romania, especially in connection with petroleum industry. In the United States, chlorination of benzene to gammexane (hexachlorocyclohexane) was hotly pursued at one time by radiation or photoinitiation. Since the early seventies the activity has dwindled, presumably due to lack of demand and environmental considerations. 

GENERATION OF RADICALS BY IONIZING RADIATION 3.5.1 Primary Radiation-Chemical Processes... 

Polymer radiation chemistry is a key element of the electronics industry, in that polymer materials that undergo radiation induced changes in solubility are used to define the individual elements of integrated circuits. As the demands placed on these materials increases due to increased density, complexity and miniaturization of devices, new materials and chemistry will be required. This necessitates continued efforts to understand fundamental polymer radiation chemical processes, and continued development of new radiation sensitive materials that are applicable to VLSI Technology. 

In gases the track structures usually contain a small number of active particles and are separated from each other by considerable distance. Owing to efficient diffusion, the initial inhomogeneity in the distribution of active particles rapidly smoothes out, and by the time the chemical reactions begin, the intermediate chemically active particles are distributed practically homogeneously in the irradiated volume. For this reason the influence of tracks on radiation-chemical processes in gaseous media... 

However, the spatial inhomogeneity in the distribution of reagents is not the only reason why the radiolysis of substances in the condensed state is different from that of gases. As we have already mentioned in Section VIII, as we pass from the gaseous state to the condensed one, at the primary stage of radiolysis we already observe a redistribution of yields of primary active particles (resulting in the increase of the yield of ionized states). Also different are the subsequent relaxation processes, as well as the processes of decay of excited and ionized states.354 Another specific feature of processes in a condensed medium is the cage effect, which slows down the decay of a molecule into radicals.355 Finally, the formation of solvated electrons is also a characteristic feature of radiation-chemical processes in liquids.356... 

The role of the track structure is most clearly illustrated by the example of radiolysis of liquids by heavy ions. In this case it is possible to vary broadly the geometric dimension of tracks and the concentrations of active particles in them. The dependence of track effects on the track structure has been studied in Refs. 365 and 366 The qualitative relation between the structure of a track and the features of radiation-chemical processes has been analysed.15,18... 

Thus, adding HN03 to the system mainly produced a redirection of the radiation-chemical processes. As a result, nitration products appeared, and the radiation-chemical yield of oxidation products (Figure 8.1 compounds II) increased, primarily due to a reduction of the radiation-chemical yield of condensation products (Figure 8.1 compounds All, I, IV, and V) (43). 

Vladimirova, M.V. 1992. Mathematical modelling of radiation-chemical processes in HN03 solutions of Pu. 3. Refined quantitative characteristics of the model for 3 and 6M HN03. Soviet Radiochem. 34(6) 711-720. (Translated from Radiokhimiya 34(6) 89-102.)... 

Ohnischi, S. ESR study of the radiation chemical processes in polyethylene. Bull. Chem. Soc. Japan 35, 254 (1962). 

The theoretical base of the spur process is Onsager s theory of the geminate pair recombination. Contrary to this, the blob model is most appropriate for consideration of early radiation-chemical processes in multiparticle track entities, such as blobs and ionization columns. The main distinction between the spur and blob comes from the large difference in the initial number of ion-electron pairs they contain. 

Tripathi GNR (1983) Time resolved resonance Raman spectroscopy of radiation-chemical processes. In Talmi Y (ed) Multichannel Image detectors, vol 2 ACS Symposium Series No. 236, American Chemical Society, Washington D.C. 

Systematic investigation of radiation-induced polymerization was conducted in Leeds by F. S. Dainton and his group (8) and in Paris by M. Magat and co-workers (9). The results of these studies convincingly demonstrated that radiation could initiate polymerization at any desired (low) temperature and led to a fundamental conclusion, viz., radiation-induced polymerizations occurred by conventional free radical mechanisms. This concept was extended to other radiation-chemical processes, and in the 1950 s most radiation chemists used free radical theories for interpreting their experimental data. 

Method of Studying Radiation Chemical Processes . CRC Handbook of Radiation Chemistry (Eds. Y. Tabata, Y. Ito, S. Tagawa), CRC Press, Boca Raton, 1991, Chap. Ill, pp. 97-186. 

E. I. Grigoriev, L. I. Trakhtenberg, Radiation-chemical Processes in Solid Pha.se Theory and Application, CRC Press, Boca Raton, 1996, and references therein. 

It has been suggested that the initial step in the radiation chemical process involves the attack of a radical from the solvent on the P4-molecule >2,5,66,117)... 

For the most part, doses quoted in this review are given in electron volts absorbed per gram of material, ev/gm. The electron volt is a suitable unit if one wishes to fix his attention on individual atomic or molecular events, and it has become generally used in radiation chemistry. The yields of radiation-chemical processes are conventionally given in molecules affected per 100 ev (symbolized by G). Thus 6r —H2O) = 4.6 means that 4.6 molecules of water are decomposed by the absorption of 100 ev of the specified radiation under the other given conditions. 

A tunable pulsed laser Raman spectrometer for time resolved Raman studies of radiation-chemical processes is described. This apparatus utilizes the state of art optical multichannel detection and a-nalysis techniques for data acquisition and electron pulse radiolysis for initiating the reactions. By using this technique the resonance Raman spectra of intermediates with absorption spectra in the 248-900 nm region, and mean lifetimes > 30 ns can be examined. This apparatus can be used to time resolve the vibrational spectral o-verlap between transients absorbing in the same region, and to follow their decay kinetics by monitoring the well resolved Raman peaks. For kinetic measurements at millisecond time scale, the Raman technique is preferable over optical absorption method where low frequency noise is quite bothersome. A time resolved Raman study of the pulse radiolytic oxidation of aqueous tetrafluoro-hydroquinone and p-methoxyphenol is briefly discussed. 

Strelko, V. V. Shvets, D. A. Kartel, N. T. Suprunenko, K. A. Doroshenko, V. I. Kabakchi, A. M. Radiation-Chemical Processes in Heterogeneous Systems on Basis of Dispersed Oxides Energoizdat Moscow, 1981. 

Reactive states of aromatic molecules in solution may be observed directly by the pulse radiolysis method. Extensive investigations of both aromatic molecule ions (particularly the radical anions) and electronically excited states have provided new information about not only the radiation chemical processes but also the general kinetic behavior of these reactive intermediates. Absolute rate constants have been determined for many elementary processes such as energy transfer and electron and proton transfer reactions. 

Although the effects of spin coherence have been mainly studied using radiation-chemical processes as an example, published are the first works on the MARY spectra of radical ion pairs produced in solutions by photoionization. Probably, there are no principle obstacles to the application of the method of quantum beats to these systems. Interpretation of results is expected to be more simple, in this case, because of the use of monochromatic sources of ionization and the absence of cross recombination effects typical of the ionization track. Another manifestation of spin coherence, observed experimentally but omitted in this review, is the beats induced by resonance microwave pumping [36-38]. The range of applications of this phenomenon for studying spin-correlated radical ion pairs has yet to be outlined. 

Radiation chemical processes near the end of its thermalization track determine the environment in which the muon is found on an experimental time scale corresponding to its lifetime, = 2.2 ps. In experiments in transverse fields we distinguish between different components according to their signal amphtudes which are converted to fiactional muon polarizations Pi, with EPj = 1.0, if the fiill initial polarization in the beam is accounted for. 

Because the energy of ionizing particles or radiations is not absorbed at a specific site or within a particular molecule, the quantum yield of a reaction involving one such particle or unit of radiation can be fairly well defined. The inherent efficiency of a radiation chemical process during resist exposure is measured in terms of a radiation chemical yield or G-value. For a process leading to a certain number of reaction products, the G-value of each is defined as the number of moles of that product resulting from 100 eV of energy deposited into the system. In a system of unit volume (1 L) the molarity of the product [P] produced by a dose D is expressed as... 

Radiation chemistry is characterized by the very fast generation of reactive species followed by extensive competition between recombination reactions and reactions with solutes. A complete description of a radiation chemical process requires information about the final products and the transient species. 

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