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inattention
will be drawn to any evidence which might serve as a
basis for future work along these lines and some tentative
suggestions which may be helpful for further work will be
included.
f
?^^g3 for the Relative Abundance of Nuclides
All species of stable nuclei occur In nature. Their
relative abundance, however, shows a variation by a factor of the
order of lO-'-^, Harklns (1917) was the first to attempt a systematic
classification of the stable nuclear species or nuclides
based upon our knowledge of atomic number as a proper
designation of an element and of the Isotopes as the ultimate
constituents of these elements, and Harkins* rules represent
important regularities in the abundances of the nuclides.
Mattauch introduced additional rules. Such rules are now in
general understood in teiras of binding energies, in particular
from the point of view of the nuclear shell model as discovered
and developed by Mayer (19^, 19*^9) and by Baxel, Jensen and
Suess {19^*9).
In a previous paper (Suess, 19^7) certain rules regarding
the abundances of the stable nuclides were presented as follows:
(1) Odd mass number nuclides: The abundances of odd mass numbered
nuclear species with A>'v50 change steadily with the mass number»
When Isobars occur, the sum of the abundances of the isobars must be
used instead of the individual abundances.
(2) Even mass number nuclides: (a) In the region of the heavier