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approach each other in pattern with passage of time.
During
the early period after the shot there is, of course, a greater
variety of radioactive isotopes present than later, and there
is some indication that selective uptake might be more marked
or selective exclusion less marked during this period.
As
the shorter-lived isotopes decay and decrease in importance,
leaving fewer radicactive materials available, the decline and
decay of radioactivity in the different tissues and species
show greater similarities.
The data presented do not permit exact distinctions be-
tween tissues or between different species on the basis of
differences in the uptake of radioactive materials.
It appears
from the decay curves and the decline trends that the fish
tissues differ mainly in orders of magnitude rather than in
quality after the first 100 days, although there is the possibility of different isotopes with similer half lives being
present.
Radiochemical analysis done within two months on fish col-
lected two to three months after shot contained Mn°4, Fe->,Co>/,
C058, 6069, and zn65, with Feo) and zn©5 as the dominant isotopes.
Fish collected within one month after the 1954 shots and analyzed
January 1957 contained 95 percent Fe55; Mn>*, Co57, and C0?
(Lowman, Palumbo and South, 1957) contributed the remainder of
the radioactivity.
There may be fission products in the fish
the first few weeks or months after the shot, but after four or
five months fission products contribute very little, if any, to
the total radioactivity in the fish.