~ 16.
III,
VARIATICN OF THE STRONTIUM-GO BODY BURDEN WITE
.OCALITY
Most important cf the causes of variation «i the
strontium-90 content of individuals with locality is, of
course, the amount of fallout in a given region.
The general
rules about the intensity of fallout have been described
above. For air-fired megaton weapons our present indication
is that the fallout is almost world-wide and for reasons
of simplicity and in the absence of better information at the
present time, we work on the model that this is a uniforn
distribution, over the entire world, of material that falls
from the stratosphere.
Further evidence and data on this
point ére rapidly being collected which will undoubtedly
settle the stratospheric horizontal mixing question.
At the present time, the general latitudes in the
Northern Hemisphere which are between 100 and 60° North have
the highest strontium-90 content.
In the United States,
which because of our proximity to the Nevada Test Site has
unusually high fallout, there are at the present time about
25 millicuries per square mile of strontium-90,
For average
soil this means 2 concentration in the top soil of at cut
50 Sunshine Units.
With the factors of discrimination mentioned above, this means that an equilibrium body burien
between 1.7 Sunshine Units and 3.9 Sunshine Units is to be
expected.
Actually, the present body burden in young chil-
¢ran indicates that the lower value is probably more realistic. The present body burden in children ~~ about 0.5
Sunshine Units -- probably was derived from an average
strontium-90 content in the top soil of something like 15
millicuries per square mile, or about 25 to 30 Sunshine
Units during the time the strontium-90 was being acquired.
Thus we find that the experimental value for the ratio
between the body burden of young children and the average
concentration in the top soil is about 50 to 1; rather
closer to the higher range of the laboratory results than
to the lowest range.
Table iI contains the latest data for the total
~
ps
bet
ha
strontium-90 fallout as measured in U. S. soils, and Figure
5 displays these data graphically.
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