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2. Sources and Nature of Fallout
The major source of radioactive miterials in fallout is the
fissioniig or 5, litting of atoms of uranium and plutonium that
in the
ives rise ton large number of unstabie radioigerepes
fusion process hydrogen nuclei are jeined together. Induced
radioactive products result when inert materials capture
neutrons that are released during either the fission or fusion
process, Generally, these induced radioactive materials are
relatively short-lived and contribute only in a minor wayto
radintion exposures to man, The principal exception ia carbon
14 described in section | F (page 16).
Sune of these rodivactive materials escape ae gases and are
dispersed and diluted in the atmosphere. Most of the fission
products, however, become incorpurated into or attached onto
minute inert particles of duat and debris from the immediate
environment of the bomb. The dust particles, together with
the associated radioactive nuclides, are ewont high into the air
by the heat and force of the nuclear explosion. The larger
particles and those in the lower levels of the cloud fall nearby.
Smaller particles in the upper levels are carried away to be
spread worldwide, The worldwide distribution of these radioactive particles follows the same pattern as would occur with
any other small particles injected into the same regions of the
atmosphere -radioactivity has essentially no effect on the
pattern of distribution.
Roughly, a nuclear detonation of one-half million tons or
less, fired at a low altitude-—but high enough eo the frebrll
does not intersect the ground results ino most of the fission
products remaining in the lower atmosphere, the troposphere.
They are deposited on the earth's surface at a rate such that
one-half of the amount remaining in the atmosphere at any one
time falis in 24 weeks (calied tropospheric residence tral
time), As the energy yields of the auclear detonation increase, more apd more of the fission products are swept higher
and higher inte the stratosphere othe layer above he trope
sphere (fig. ve
The residence badtdime bere ap inore Tie one
half a vear for ingection mite the becer stratonghere
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Various
radiation such as Che roentgen, rep, rem, and rad. All are in
tended to express some relationsh. + between the radiation
energy absorbed and biological effects. Since it is mot critieal
for the following discussions to understand the technical ditferences among the units, only the “reentgen” will be used. To
provide some perspective ag to the magnitude of the “roentgen” table Lis inehided,
ue
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regionsand one year or somewhat less al the equator,
active debris from nuclear detonations covurringae y
altitudes (about $0 miles and higher siay have ag
half-time of five years or more.
‘
Roughly two-thirds of the radioaclive partieulat
injected into the lower stratesphere ul the north pola
has been observed to full in the 80° 6u° North latity
where about S0 percent of the world’s pupulation Nv
tion at the equaturial repions has been observed te |
8 more even distribution belween the two hemisph
For surface bursts of high Gnillion ton range) ylel
50-80 percent of the radioactive debriy is deposited eg
fallout,” Le. within 24 hours. Air buiscs -where the
does not approach the surface — result in istle, any, b
out.
Table 2 tabulates some of the key data on estimated
energy yields from all past nuclear weapoistests. OF
energy relensed of FEE million tons equisatent of TNT:
TABLE 2.0
Fatimates of Vietde from Atl oc ae Wengions Ty
aT
Tetal million toon!
Feseion millon Cet
Fissrerpy pid iiuay Geet cet beck pedeebeasi he
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