.
‘
Volume 66, No. 6
June 1967
LATE EFFECTS OF RADIOACTIVE IODINE IN FALLOUT
by such an explosion and its widespread
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distribution has caused a series of high-
energy discussions, and sometimes I think
the temperature achieved by these discussions has approximated that of the cloud
itself.
I will make a few general remarks about
four different aspects of fallout from nuclear
explosions. The first concerns explosive nu-
onanSE TET, te
aweSane a SE,
clear devices; the second, radioactive prod-
ucts from these devices; the third, local factors influencing the distribution of these
products; and finally, the biological modu-
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lation of the fallout products.
Nuclear explosive devices are of two
types, the first being the fission reaction
that generally involves **5U, ?8°U, or plu-
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94
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142
MASS NUMBER
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166
tonium. The fission produces an enormous
variety of radioisotopes. There are also fu-
Ficurz 1. Yield of various isotopes from nuclear reactions involving ™U and ™Pu.
that we are presently discussing was a fusion explosion. However, all the fusion explosions have to be triggered by a fissiontype explosion in order to achieve the
sion that produces either helium ortritium,
may decrease, and finally there may be a
relatively smooth curve. In general, however, fission produces an abundance ofisotopes with mass around 136 and mass around
94. Just why fission occurs asymmetrically is a matter of someinterest I will not
discuss. It might be noted that most of the
radioactive isotopes of iodine have a mass
between 13] and 135 and hence are major
fission products.
There is an additional point of interest,
and neutrons or, in the case of tritium, a
namely, neutron excess. ?85U (a common fis-
sion explosions, and the Bikini explosion
necessary temperature required for fusion,
whichis of the order of 10 to 100 million K.
The fusion explosions are of two types:
Theyare either the deuterium-tritium fusion
that produces helium plus neutrons and
energy, or the deuterium-deuterium explo-
proton, plus energy. The points to remem-
ber are [1] fusion explosions are impossible
without fission so that there are always
sionable material), for example, has 92 protons in the nucleus and 143 neutrons. If
this were to undergo fission directly and
fission gives an enormous increase in the
There is an extensive series of palladium
fission products, and [2] fusion added to
number of neutrons present, and this has an
effect on the distribution of the radioactive
decay products.
As far as the products themselves are
concerned, there 1s an interesting distribu-
tion curve (Figure 1). There are peaks at
about 136 mass units and at about 94 mass
units for the fission of 73U. There is a
isotopes, and the most abundant of the
stable ones is 1°°Pd, which has exactly half
the number of protons of uranium. But
since it has a mass of 106, it has 60 neu-
trons. Therefore, if there were symmetrical
fission of #85U, one would obtain 2 atoms
of palladium and an excess of 23 neutrons.
This implies that in a fission explosion
there is an enormous neutron flux in the
explosive’ device that irradiates the © fission products, the container, and anything
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slightly different curve for fission of 78*Pu
and 755U, If the fission occurs in the presence of very high-energy neutrons the peaks
symmetrically, it would produce palladium.