A. Theoretical and Instrumental Background
I. Definition of Isotopes
Isotopes may be defined as atoms whose nuclei contain the same
number of protons but a different number of neutrons. The term "isotopes" is derived from Greek (meaning equal places) and indicates that
isotopes occupy the same position in the periodic table.
It is convenient to denote isotopes in the following form: IgO, where
the superscript 16 represents the mass number and the subscript
8 represents the atomic number.
Isotopes can be divided into stable and unstable (radioactive) species.
The number of stable isotopes is about 300; whilst over 1200 unstable
ones have been discovered so far. The term "stable" is a relative one, it
depends on the detection limits of radioactive decay times. In the range
of atomic numbers from 0 to 83, stable nuclides of all masses except 5
and 8 are known. Only 21 elements are pure elements, in the sense that
they have only one stable isotope. All other elements are mixtures of at
least two isotopes. In some elements, the different isotopes may be present in substantial proportions. In copper, for example, 63CU accounts for
69% and 65CU accounts for 31 %. In most cases one isotope is predominant, the others being present only in traces.
The stability of nuclides is characterized by several important rules,
two of which are briefly discussed here. The first one is the so-called
symmetry rule, which states that in a stable nuclide with a low atomic
number, the number of protons is approximately equal to the number of
neutrons, or the neutron to proton ratio, N/Z, is approximately equal to
unity. In stable nuclei with more than 20 protons or neutrons, the N/Z is
always greater than unity, with a maximum value of about 1.5 for the
heaviest stable nuclei. The electrostatic Coulomb repulsion of the positively charged protons grows rapidly with increasing Z. To maintain
stability in the nuclei, electrically neutral neutrons are incorporated
more rapidly than protons (see Fig. 1).
The second rule is the so-called Oddo and Harkins rule, which states
that nuclei can be classified in terms of containing even or odd numbers
of protons (Z) and neutrons (N). Of the four possible combinations, the
most common arrangement is even-even, the least common odd-odd, as
shown in Table 1.
I. Definition of Isotopes
Isotopes may be defined as atoms whose nuclei contain the same
number of protons but a different number of neutrons. The term "isotopes" is derived from Greek (meaning equal places) and indicates that
isotopes occupy the same position in the periodic table.
It is convenient to denote isotopes in the following form: IgO, where
the superscript 16 represents the mass number and the subscript
8 represents the atomic number.
Isotopes can be divided into stable and unstable (radioactive) species.
The number of stable isotopes is about 300; whilst over 1200 unstable
ones have been discovered so far. The term "stable" is a relative one, it
depends on the detection limits of radioactive decay times. In the range
of atomic numbers from 0 to 83, stable nuclides of all masses except 5
and 8 are known. Only 21 elements are pure elements, in the sense that
they have only one stable isotope. All other elements are mixtures of at
least two isotopes. In some elements, the different isotopes may be present in substantial proportions. In copper, for example, 63CU accounts for
69% and 65CU accounts for 31 %. In most cases one isotope is predominant, the others being present only in traces.
The stability of nuclides is characterized by several important rules,
two of which are briefly discussed here. The first one is the so-called
symmetry rule, which states that in a stable nuclide with a low atomic
number, the number of protons is approximately equal to the number of
neutrons, or the neutron to proton ratio, N/Z, is approximately equal to
unity. In stable nuclei with more than 20 protons or neutrons, the N/Z is
always greater than unity, with a maximum value of about 1.5 for the
heaviest stable nuclei. The electrostatic Coulomb repulsion of the positively charged protons grows rapidly with increasing Z. To maintain
stability in the nuclei, electrically neutral neutrons are incorporated
more rapidly than protons (see Fig. 1).
The second rule is the so-called Oddo and Harkins rule, which states
that nuclei can be classified in terms of containing even or odd numbers
of protons (Z) and neutrons (N). Of the four possible combinations, the
most common arrangement is even-even, the least common odd-odd, as
shown in Table 1.