-4due to the slightly higher fission yield. The cont nt of
radiocesium in rainwater is comparable to that of
contiume
90. Also, the content of radiocesium in the human ody as
measured by Marinelli at Argonne and Anderson and — uagham
at Los Alamos agrees well with the fact that it has an
average residence time in tne human body of about f ve
months as compared to many years for strontium-90.
The
radiocesium data are very interesting because of their
bearing on tne fallout dissemination mechanism and the
confidence with which we can establish the probable future
-behavior cf radioactive strontium. The data confirm pre_ Vious sugsestions as to the dissemination mechanism, that
is, we find that radiocesium fallout except of the local
variety is carried down very largely in the form of moisture droplets and that there is some direct pick-up by
leaves and grass on surfaces.
It is captured and held
tightly cy the top two inches of most soils, so the water
which falls and runs off in the form of rivers is clean
by the time it has drained a short distance through soil.
All of this is very similar to the radiostrontium behavior.
The plants pick the strontium-90, and radiocesium
to a lesser extent, out of the soil and also off of their
leaves and take it into their systems. There appea.s to be
a discrimination mechanism which operates in most plants so
that the strontium-90 content of the plant is consivierably
less relative to its calcium content than in the case of the
soil.
On the average, the discrimination factor between the
top soil and plants against strontium relative to calcium
seems to be about 1.4.
When the cows eat grass they further
discriminate by about a factor of 7 in making milk 30 there
is an over-all protection factor for strontium-90 from the
top soil to milk of about 1.4 x 7 or 10. Also, there is a
further discrimination factor against strontium relative t
calcium in the human body. This factor is not known too
well, but is known definitely to be at least as large as 2
and is thought possibly to be as high as 8.
now in progress to settle this.
Researches are
Therefore, there is a series
of protective factors which makes the concentration of radiostrontium derived from milk relative to calcium in human bone
not over 1/20 and possibly as little as 1/80 of that in the
“7
top soil.
Of course, it shouid be pointed out that there is
considerable part of the fallout which is picked up directly
on the leaves and to this the factor of 1.4 does noc apply,
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