Table 1— POTENTIALLY HAZARDOUS RADIONUCLIDES IN FALLOUT FROM
NUCLEAR DETONATIONS
Fission*
Radionuclide
Type of
radiation
abundance,
%
Radiol.
half life
Pua
Sr*?
Cs
Pm‘?
Celt
a
B
By
B
Bay
5.0
6.2
2.6
5.3
24,000 yr
27.7 yr
26.6 yr
2.64 yr
285 day
yi
B
Bal?
ps!
By
By
zs
sr
Nb"
By
B
By
6.4
5.9
4.6
6.4
6.0
2.8
65 day
58 day
51 day
35 day
13 day
8 day
Totalt
production,
megacuries
0.3
5.5
7.2
30
200
1100
1150
950
2000
5000
4000
Abs. on
ingestion,
%
Body MPL,
pe
3x 103
30
100
1x 107?
1x 107?
0.037
1.0
54
60
5
1 x 107?
1x 107?
30
1x 107?
5
100
26
5
4
76
4
0.7
*Slow neutron fission of U™*; abundance in weapon debris is somewhat different.
{ Total initial activity in megacuries produced by all weapons tests to mid-1957.
fission by neutron interaction with bomb components. Since 1 kiloton of fission yield is pro-
duced by 1.4 x 10° fissions,® each of which results in the production of a Pu’** atom, 55 mega-
tons of fission would produce 0.2 megacuries of Pu?**_ Other isotopes of plutonium, when con-
verted to equivalents of Pu*®®, bring the total production to about 0.3 megacurie equivalents.
The production values given in Table 1 are not a measure of the relative biological importance
of the various nuclides, but merely provide some general idea of the relative initial activities
produced by all weapons tests through mid-1957. Development of sufficiently sensitive detec-
tors should result eventually in detection of most of these radionuclides in foods and man.
Strontium-90 (references 5 and 6), Cs'*" (reference 7), and I'*! (reference 8) have been meas-
ured quantitatively in the human body, and the presence of Cein pooled urine samples has
been reported.® In addition, Ba!° (reference 10) and Sr®™(reference 11) have been observed
in milk, and other radionuclides have been detected in air and other materials composing man’s
environment. The extent to which they pose a potential threat to man’s health and well-being
depend on their rate of production and on their individual physical and biological properties.
3
3.1
DISTRIBUTION OF FALLOUT FROM NUCLEAR DETONATIONS
Postulated Mechanisms of Distribution
Libby®’was first to propose a model explaining fallout and distribution of atomic debris
from nuclear weapons detonations. His model is based on three kinds of fallout —local,
tropospheric, and stratospheric.
Local fallout is deposited in the immediate environs of the explosion during the first few
hours. This debris consists of the large particles from the fireball and includes partially or
completely vaporized residues from the soil and structures which are swept into the cloud.
Tropospheric fallout consists of that material injected into the atmosphere below the
tropopause which is not coarse enoughto fall out locally. This debris is sufficiently fine that
it travels great distances, circling the earth from west to east in the general latitude of the
explosion, until removed from the atmosphere (with a half-time of 20 to 30 days) by rain, fog,
contact with vegetation, and other meteorological and/or physical factors.
Stratospheric fallout is composed of fission products that are carried above the tropopause
and can result only from large weapons (of the order of 1 megaton and greater). Libby!3)> has
postulated that atomic debris, once it is injected above the tropopause, is mixed rapidly
throughout the stratosphere and falls back uniformly into the troposphere with a half-time of
about 7 years. As it returns to the troposphere, it is deposited over the earth’s surface in
relation to meteorological conditions. He attributed the higher Sr” soil concentrations in the
rn
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