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).
Last Modified: June 28, 2012
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