Chemistry, radiation

11 Radiation damage to other molecules of biochemical interest is examined briefly on p. 50. 

Other complexities are revealed when frozen solutions of spin trap in methanol are irradiated, and the solution is then melted. The proportions of spin adducts are markedly dependent on radiolysis temperature. One contributory factor is undoubtedly the reaction of MeO with neighbouring methanol in the solid matrix, to produce HOCH2, before diffusion to reach spin-trap molecules is possible. 

Despite the ambiguities remaining with this system, Sargent (1977b) has extended the liquid-phase experiments to determine kT for trapping methoxyl radicals by MNP in methanol. The procedure depended on comparison with 

For aqueous solutions, Sargent and Gardy (1976) have advocated the use of DMPO, which gives persistent spin adducts with hydroxyl radicals hydrogen-atom adducts arise by electron scavenging and subsequent protonation of DMPCK, but this can be minimized by incorporating N20 in the system, which traps electrons and raises the yield of hydroxyl radicals (28). 

An interesting extension of aqueous solution radiolysis involved solutions of sodium dodecyl sulphate in the presence of MNP. Spin adducts of secondary alkyl radicals were detected provided that the critical micelle concentration of the surfactant was exceeded. Whilst it was rather loosely concluded that there is a marked catalytic effect of micelles on the rates of reaction of radicals with nitroso spin traps , no single origin of this effect could be clearly identified (Bakalik and Thomas, 1977). 

Radiation chemistry is now a well-established area of science that deals with chemical and physicochemical changes produced by the absorption of high-energy radiation (HER) by matter. The subject covers events that occur from the passage of the ionizing particle to the completion of chemical reactions. To encompass the enor- 

The two fundamental processes that result from radiochemical reactions are chain scission and crosslinking, characterized by Gg and Gx, respectively. If Gg 4Gx, branched polymers can be formed and may eventually evolve into a three-dimensional network structure. Based on the assumptions that  

Charlesby and Pinner have shown that the sol fraction(s) should follow Eq. (74), 

As a result of the earliest observations on the radiolysis of water, it was suggested that hydrogen atoms and hydroxyl radicals were the principEil reactive species [1]. Two theories were proposed to account for the formation of these. 

The first [2] supposed that an electron ejected from a water molecule by the radiation is thermalized before it escapes the coulombic attraction of the parent positive ion. Its lifetime is too short for it to exist as a significant reaction intermediate and it is recaptured to give an excited molecule which subsequently decomposes, viz. 

Alternatively, Stein [3] and also Platzman [4] proposed that the hydrated electron could be an important intermediate in the radiolysis of aqueous systems. Platzman suggested that the rate of energy loss of the ejected electron was such that it would escape the coulombic field of the parent positive ion before thermalization. Subsequently the electron would be hydrated, i.e. the electron polarizes the dielectric and then is bound in a stable quantum state to it, viz. 

As will be seen subsequently, later experimental evidence verified Platzman s postulate. 

In the late 1950s several experiments indicated that the reducing species was not simply the hydrogen atom. In neutral solutions, the hydrogen atom formed by the reaction 

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J. E. Wilson, Radiation Chemistry of Monomers, Polymers, andPlastics, Marcel Dekker, Inc., New York, 1974. 

Mozunder, A. (1999J Fundamentals of Radiation Chemistry, Academic Press, Kmgston-upon Thames. Wright, M.R. (1999J Fundamentals of Chemical Kinetics, Florwood Publishing, Flemel Flempstead. 

Tabata, Y, Ito, Y. and Tagawa, S., CRC Handbook of Radiation Chemistry. CRC Press, Boca Raton, FL, 1991. 

The radiation chemistry has been mainly discussed in terms of degradation reactions (as above) involving the loss of gaseous products and the irreversible change of the stoichiometry [203]. However, more recent results showed that polymers irradiated with radiation deposit-... 

Polyethylene cured by the chemical and radiation-chemistry methods undergoes thermal destruction upon heating as in normal polyethylene. Thermoslabiliz-... 

A. Chapiro, Radiation Chemistry of Polymeric System, Interscience Publishers, New York (1962). 

A. J. Swallow, An Introduction To Radiation Chemistry, Longman, London (1973). 

R. Azzam 5th Tihany Symp. on Radiation Chemistry Proc., 771 (1982). 

K. Friese and F. Tannert, Proceedings of the 7-Tihany Symposium on Radiation Chemistry. Budapest (Hun-gary/Hungarian Chemistry Society) p. 367 (1991). 

Radiation, chemistry, 191 resistance, 194, 199 Radical polymerization, 159 Relaxation times for mixed crystals, 191 Resonance, lines, 189, 190, 192, 202, 203 structures, 189... 

Detailed studies on radiation chemistry of PEO have been performed [74-77]. Upon y-irradiation, the gel-dose drops abruptly along with an increase in the concentration and molecular weight of the polymer, thus reaching values of 0.15-0.25 Mrad in the range of practical interest [75]. Oxygen is a strong inhibitor and when it is carefully removed from the solution, crosslinking of PEO occurs at doses as low as 0.01 Mrad [76]. 

Chapiro A (1960) Radiation chemistry of polymeric systems Wiley-Interscience, New York... 

Radiatsionnaya khimiya polimerov (radiation chemistry of polymers) Moscow Nauka,... 

The study of radiation chemistry might be divided, from the experimental point of view, into two parts. The first is the study of unstable intermediates which have short lifetimes and thus cannot be studied by the usual methods of chemistry. The second part is the study of the final products of the radiolysis which are measured by common chemical techniques. 

J. H. O Donnell and D. F. Sangster, Principles of Radiation Chemistry, Edward Arnold, London, 1970. 

The skillful and dedicated collaborative efforts of members of the ANL Chemistry Division Radiation Chemistry Group, S. Gordon, W. Mulac and K. H. Schmidt have provided not only the technical expertise but also continuing intellectual stimulation which has made the pulse radiolysis studies possible. 

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