1 General Features of Radioisotopic Methodology
and Measurement of Radioactivity
1.1 Physical Background
Radioisotopes are used in aquatic ecology to label molecules of organic and
inorganic substances or to label organisms - hydrobionts whose dynamics,
transformations in time, or migrations in space with the aid of these labeled
molecules can be traced (Sheppard 1962). Therefore the scope of these
methods was otherwise named radiolabeling or tracer methods. The molecules
are "labeled" by including into them atoms of radioisotopes of the same elements. As labels radioisotopes are greatly preferable to other ways of labeling like staining, or the use of fluorescence or stable elements of isotopes. In
fact, they represent ideal labels, because they do not undergo cbemical reactions or change during the chemical transformation of labeled molecules.
The rate of radioactive disintegration as evidence of the presence of a definite
quantity of labeled molecules does not depend on any physical or chemical
condition, such as temperature, pressure, pH, or redox potential, being a purely
statistical process. The chemical and physical properties of radioisotopes as
chemical elements completely coincide with the corresponding properties of
the natural isotopes of the same elements and molecules they compose. As
labels, radioisotopes are extremely sensitive. Their presence as admixture can
be discovered by counting individual radioactive disintegrations at quantities
less than 10- 1U _1O- 1S mg.
Radioisotopes are varieties of nuclides of the same chemical elements,
which differ by their masses because of the varying contents of neutrons in
their nuclei; but their chemical and electrostatic features remain the same as
in stable natural isotopes. The atomic species of nuclides X are specified by
defining their nucleic characteristics, e.g., by defining their mass number a and
their atomic number z: nuclide = X~. The mass number a is defined by the total
amount of heavy-particle neutrons and protons in the nucleus, and the atomic
number z by the amount of only charged particle protons. The atomic number
is the chemical symbol of a given nuclide, which is equal to the change of
its nucleus. It corresponds to the position of a given group of nuclides in the
Periodic Table of Elements and is responsible for its chemical properties. Thus,
the isotopes of a given element have a similar atomic number z but differ in
their mass number a. The difference in mass numbers a in nuclides with the
similar atomic number z entails in some of them a definite instability in their
nuclei, which is followed by their statistical disintegration. Such isotopes and
disintegrating nuclei represent radioactive isotopes, because the disintegra-
and Measurement of Radioactivity
1.1 Physical Background
Radioisotopes are used in aquatic ecology to label molecules of organic and
inorganic substances or to label organisms - hydrobionts whose dynamics,
transformations in time, or migrations in space with the aid of these labeled
molecules can be traced (Sheppard 1962). Therefore the scope of these
methods was otherwise named radiolabeling or tracer methods. The molecules
are "labeled" by including into them atoms of radioisotopes of the same elements. As labels radioisotopes are greatly preferable to other ways of labeling like staining, or the use of fluorescence or stable elements of isotopes. In
fact, they represent ideal labels, because they do not undergo cbemical reactions or change during the chemical transformation of labeled molecules.
The rate of radioactive disintegration as evidence of the presence of a definite
quantity of labeled molecules does not depend on any physical or chemical
condition, such as temperature, pressure, pH, or redox potential, being a purely
statistical process. The chemical and physical properties of radioisotopes as
chemical elements completely coincide with the corresponding properties of
the natural isotopes of the same elements and molecules they compose. As
labels, radioisotopes are extremely sensitive. Their presence as admixture can
be discovered by counting individual radioactive disintegrations at quantities
less than 10- 1U _1O- 1S mg.
Radioisotopes are varieties of nuclides of the same chemical elements,
which differ by their masses because of the varying contents of neutrons in
their nuclei; but their chemical and electrostatic features remain the same as
in stable natural isotopes. The atomic species of nuclides X are specified by
defining their nucleic characteristics, e.g., by defining their mass number a and
their atomic number z: nuclide = X~. The mass number a is defined by the total
amount of heavy-particle neutrons and protons in the nucleus, and the atomic
number z by the amount of only charged particle protons. The atomic number
is the chemical symbol of a given nuclide, which is equal to the change of
its nucleus. It corresponds to the position of a given group of nuclides in the
Periodic Table of Elements and is responsible for its chemical properties. Thus,
the isotopes of a given element have a similar atomic number z but differ in
their mass number a. The difference in mass numbers a in nuclides with the
similar atomic number z entails in some of them a definite instability in their
nuclei, which is followed by their statistical disintegration. Such isotopes and
disintegrating nuclei represent radioactive isotopes, because the disintegra-