Radiation Induced Chemical Reactions 1947-67

Brookhaven over the last twenty years has taken a leading role in the study of chemical effects of radiation and in the conversion of this subject from empirical groping to a sophisticated branch of chemical science. The aim in this field is, first, to infer what reactions actually are produced by radiation in various systems, in terms of the nature and behavior of the chemical species formed in intermediate stages of the over-all process, and, second, to explain how these reactions are brought about by electronic excitation of the irradiated material.

Aqueous solutions

Understanding radiation effects in water is basic both to fundamental radiobiology and to design and control of water-moderated reactors. The nature of the reducing and oxidizing radicals formed in water irradiation was first demonstrated here. It was shown by a study of salt effects that the predominant reducing species has a negative charge and is a hydrated electron. This not only introduced an important new species to chemistry, but also made possible the first correct treatment of water decomposition and re-formation in nuclear reactors.

Accurate measurement of absolute reaction rates of the hydroxyl and perhydroxyl radicals in irradiated water, difficult to make because [the reactions are] so rapid, were also first done here. Now a great many laboratories are engaged in studying formation, properties, and reaction rates of the hydrated electron and of the hydroxyl and other radicals.

A new superoxide of hydrogen, H203, was first found and characterized at BNL.

N. F. Barr and A. O. Allen, "Hydrogen Atoms in the Radiolysis of Water," J. Phys. Chem. 63, 928 (1959).
H. A. Schwarz, "Determination of Some Rate Constants for the Radical Processes in the Radiation Chemistry of Water," J. Phys. Chem. 66, 255 (1962).
G. Czapski and H. A. Schwarz, "The Nature of the Reducing Radical in Water Radiolysis," J. Phys. Chem. 66, 471 (1962).

Organic liquids

The physical processes underlying chemical changes in irradiated liquids are not as clear-cut as in gases or in ionic or valence-bonded crystals. The slowing down and capture of free electrons formed in liquids by ionization are not well understood. One approach to this problem is to measure the number of free ions which escape immediate recombination. The first complete absolute measurement for an organic liquid of this quantity and of its temperature coefficient was made at Brookhaven; the results have led to some improved theories of the processes of electron moderation. Recently made measurements of ion yields in various liquids have shown surprising differences between related compounds, which points up the degree of ignorance that still prevails in this field.

A. Hummel and A. O. Allen, "Ionization of Liquids by Radiation. I. Methods for Determination of Ion Mobilities and Ion Yields at Low voltage," J. Chem. Phys. 44, 3426 (1966).
A. Hummel, A. O. Allen, and F. H. Watson, Jr., "Ionization of Liquids by Radiation. II. Dependence of the Zero-Field Ion Yield on Temperature and Dielectric Constant," J. Chem. Phys. 44, 3431 (1966).

Heterogeneous systems

Systems of interest in biology and technology are often not pure substances or simple solutions but heterogeneous systems containing many different material phases. The effects of radiation on heterogeneous systems were first looked at here and the interesting result was found that energy initially taken up in a solid was transferred to molecules adsorbed on its surface, where it selectively excited certain states and thus produced specific modes of decomposition. Study of such systems has been taken up at many other laboratories.

J. G. Rabe, B. Rabe, and A. O. Allen, "Radiolysis and Energy Transfer in the Adsorbed State," J. Phys. Chem. 22, 1098 (1966).

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Last Modified: June 28, 2012