-7NUCLEAR RADIATION
From an exploding atomic tomb about 6% of the
energy is delivered in the form of immediate nuclear radi-
ation while about 11% of the total energy is released as
nuclear radiation over a long period of time by fission
products and induced radioactivity.
Although the intensity
and total amount of radioactivity in an area under attack
are very much dependent upon the circumstances of the
detonation, it is useful to assume that the total radioactivity, both immediate and delayed, will scale as the
first power of the total energy yield of the bomb.
Not only does the gamma radiation follow the
inverse square law with distance but in addition there are
absorption and scattering of gamma photons by the air so
that for the smaller weapons the total transmission is
effectiveiy limited to the general region of blast damage.
The neutron flux transmission is inherently more complicated and there are situations under which neutron
exposure may contribute a large fraction of the total
radiation injury.
The reaction of neutrons in air, however, is such that one would not expect significant neutron
fluxes at a distance of greater than 1500 meters from the
fireball.
It therefore appears that as the yield of nuclear
weapons increases, the blast and thermal effects tend to
outrun those of the immediate nuclear radiation.
The celayed nuclear radiation mentioned previously
may, however, vignificantiy medify the situation.
With an
air burst, where the fireball does not come into contact
with the earth, the radioactive products of the detonation
are carried high into the stmosphere as very small particles
and are scattered widely by the winds.
Tre great bulk of
this material will undergo radioactive decay before the
particles have fallen to the earth.
When, however, the
detonation is such that the fireball rests upon the ground,
great amounts of earth are crawn inte the rapidly rising
fireball resulting in coarse, highly radioactive particles
which tend to fall rapidly while being carried along by
the wind.
In such cases, there is an area of highly radioactive fallout in which the maximum intensity may be lethal
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