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37
value. Undoubtedly a marked decrease in the even mass
abundance curve occurs at mass 120 and a smaller decrease
at 119 or 121 in the odd mass curve. Qoldschmidt states
that the selenium-tellurium ratio, based on data by the
Noddacks (1934), "may perhaps" give the right 03?der of
magnitude, and he estimated it as 80. We use a value of
11.5 for the atomic ratio which may not be unreasonable.
The value for xenon is fixed relative to the krypton
value by reasoning presented above. The krypton-xenon
ratio is either 12.5 or greater, and we are assuming the
maximum possible value for xenon. The unusual abundances
of its odd mass isotopes and their relation to the even
mass abundances require maxima in both the odd and even
mass curves near mass number 130. A barium abundance
of 8 ppm in chondrites has been given recently by Pinson,
Ahrens, and Franck (1953). Kiis gives an atomic abundance
of 8.8. Our selected value of 1.83 is thus much lower.
Barium is concentrated in the earth's surface regions to
as high or even a higher degree than potassium, and hence
the reduction in the observed abundance is Justified to
some extent. We would prefer to use a higher abundance,
but, then if the smooth curve in the rare nuclides of Sn
to Ce (See Pig. 1) is to be preserved, a higher abundance
of xenon and tellurium would be required. This in turn