Radiometric Techniques for Tracing and
Identifying Industrial Wastes
FRED L. SMITH
and
C. J. LEWIS
Directors of Research
Colorado School of Mines Research Foundation, Inc.
Golden, Colorado
This paper is concerned with radiometric techniques for analyzing, controlling, and identifying industrial wastes. The coal and metal mining industries have long been aware of air and stream pollution, and have been forced
to solve problems such as mine drainage, tailings disposal, off-gas effects
from smelting operations, and many other such things. The further processing
of the ores and concentrates into various metals and nonmetals and into chemical compounds of one kind or another gives the mineral industries an additional awareness of and interest in the safe, expeditious, and economical
handling of industrial wastes.
Radiochemical methods have proved fruitful in many geological, metallurgical, and chemical situations and, since industrial waste problems are
in these disciplines, radiochemical methods should be equally useful here.
Most of the things to be discussed are being applied in the mining and chemical processing industries and are certainly applicable to waste problems.
Some of the ideas will have to be evaluated for the particular problem at hand
and one or two of the ideas are far out in the blue and may never be practical.
Because radiochemical methods depend upon the use of radioactive isotopes, it may be worthwhile to discuss isotopes briefly. Radioisotopes are
simply unstable atoms that do not differ chemically from the stable atoms of
the same element but do have a nuclear structure that cannot exist indefinitely in nature. Because the chemical properties of atoms depend on the outer
shell of electrons, the radioactive atoms act chemically just as if they were
ordinary nonradioactive atoms. The unstable structure eventually breaks
down and in doing so emits radiation that enables one to detect the presence
of the unstable atoms. The radiation that is emitted may be the heavy, intensely ionizing alpha particles that can be stopped by a very thin sheet of
foil; it may be the light beta particles -- either positively or negatively
charged electrons that can penetrate or be reflected from thin materials; but
in most cases it will be penetrating gamma photons. Of course, mixtures of
these radiations may occur.
So far, some 1, 300 isotopes have been identified in nature or produced
by man. Of this number, 279 are stable and the rest are radioactive. This
large number of existing isotopes gives a broad basis for great versatility in
industrial applications.
The isotopes we are most concerned with are produced by fission of
uranium, neutron capture, or transmutation. When a uranium or thorium
atom intercepts a neutron -- that is, an uncharged particle of unit atomic
mass --it may split up in any of over 30 different ways. Numerous isotopes
are formed directly in the fission process and begin to decay into other radio-
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