Radiolytic aspects

Radiolytic ethylene destruction occurs with a yield of ca. 20 molecules consumed/100 e.v. (36, 48). Products containing up to six carbons account for ca. 60% of that amount, and can be ascribed to free radical reactions, molecular detachments, and low order ion-molecule reactions (32). This leaves only eight molecules/100 e.v. which may have formed ethylene polymer, corresponding to a chain length of only 2.1 molecules/ ion. Even if we assumed that ethylene destruction were entirely the result of ionic polymerization, only about five ethylene molecules would be involved per ion pair. The absence of ionic polymerization can also be demonstrated by the results of the gamma ray initiated polymerization of ethylene, whose kinetics can be completely explained on the basis of conventional free radical reactions and known rate constants for these processes (32). An increase above the expected rates occurs only at pressures in excess of ca. 20 atmospheres (10). The virtual absence of ionic polymerization can be regarded as one of the most surprising aspects of the radiation chemistry of ethylene. 

Nevertheless, the radiolytic (and hydrolytic) stability of an extractant must be considered not only from the quantitative, but also from the qualitative aspect. The objective is not perfect resistance to the aggressive medium, but sufficient for an industrial implementation of the process. The nature of the stable compounds, their distribution in the process steps, and their impact are also important when proposing an efficient solvent cleanup. For such studies, dedicated representative loops in which the main treatments, extraction-irradiation-stripping-solvent treatment, could be run on the solvent are of key importance. 

A major chemical effect of y-rays on simple peptides such as the N-acylamino acids under oxygen-free conditions, both in the solid state and in concentrated aqueous solution, leads to formation of labile amidelike compounds which are readily degraded on mild hydrolysis to yield ammonia as a characteristic product. Several classes of nitrogen-deficient products are formed concomitantly with the ammonia. Earlier communications have discussed certain limited aspects of the radiolytic lability of simple peptides in the solid state and in concentrated solutions (9, 10, 18). The radiation chemistry of these systems is more complex than that involved in the radiolysis of simple peptides in dilute oxygen-free aqueous solution under which conditions main-chain degradation is of minor importance (10). In this paper we report detailed experimental evidence... 

The water chemistry of CANDU reactors embraces control of corrosion and corrosion-product transport in the coolant system, control of radiolytic decomposition of the moderator (51) and control of the concentration of soluble neutron absorbers used to adjust reactivity and control of boiler-water chemistry to minimize tube corrosion (52). The major chemical engineering effort has dealt with coolant technology and I will confine this review to that aspect of water chemistry. 

It is not practical to cover every topic in this review in which radiation chemical techniques have contributed to the understanding of catalyst function or catalytic reactions. With this introduction as a cursory guide to relevant topics, we move on to a discussion of the radiolytic spin labeling technique for analyzing products of catalytic reactions in zeolites, which has been the main thrust of experiments directed at fundamental aspects of catalysis in our laboratory. 

Several reviews were already published about radiolysis of amino acids (7, 10), proteins in the solid state (11) or in aqueous solutions (2, 3, 7, 12). In this review, our aim is not only to present most recent data but also to give an overview of the unknown aspects in protein radiation chemistry as well as in some of the expected biological consequences of protein radiolytic modifications. 

Doudna, C. M., Bertino, M. F., Blum, F. D., Tokuhiro, A. T., Lahiri-Dey, D., Chattopadhyay S., Terry, J. 2003. Radiolytic synthesis of bimetallic Ag-Pt nanoparticles with a high aspect ratio. J. Phys. Chem. B 107 2966-2970. 

Comparative studies are indeed effected especially for aqueous solutions. However, many important differences exist, and the existence of hydrated electrons in the products of water sonolysis are still controversial. In addition, many sonolyses occur primarily in the gas phase of the bubble, while radiolytic reactions occur in the solution. A major limitation, of importance for synthetic chemists, is that little is known concerning the basic aspects of cavitation in organic media, but the situation is still worse concerning their behavior under radiolysis. 

Let us now consider some quantitative aspects of radiolytic initiation. The radiolytic yield, G value, is defined as the number of molecules that react per 100 eV of absorbed energy. 

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