ova 1700-7
17.2
17.2.1
THERMAL RADIATION
Introduction
General Characteristics of Thermal Radiation
Immediately after it forms, the fireball of a nuclear detonation
starte to emit the infrared, ultraviolet, and visible light known as
thermal radiation. This emission occurs in two pulses, shown in
idealized form in Figurel7-l. During the first pulee of extremely
short duration (0.1 sec or less), temperatures in the fireball are very
high, and energy emission rapidly rises to a maximum and rapidly declines to a minimum. The second pulee may last for several seconds,
temperatures are lower, and there is a less rapid rise in energy
emission to the second or final maximum, followed by a comparatively
Blow decline to zero.
Since temperatures during the first pulse are
very high, most of the emitted radiation is in the ultraviolet region,
which is attenuated rapidly in air.
Furthermore, only about 1% of the
total thermal radiation appears in the first pulse because it has such
@ short duration and because the radiating area is still relatively
small.
Thus, the radiant exposure from the first pulse, at some dis-
tance from the burst is insignificant. During the second pulse, most
of the radiation falls in the infrared and vieible regions, and can
cause fires to start when combustible materials are directly exposed
to the fireball at sufficiently close range.
The thermal radiation from nearly all underwater bursts will be
absorbed through vaporization and dissociation of the water, and thus
is of no concern as a weapons effect.
However, thermal radiation from
surface or extremely shallow underwater bursts is of concern, although
such radiation can affect only the exposed topside personnel and
materiel of e surface ship.
Any opaque object along the firebdall-to-
target line of sight will furnish full protection from thermal radiation;
thus, topside personnel or materiel in the shadow of the ship's superatructure or topside gear would be shielded from thermal radiation. Such
radiation probably will not start shipboard fires, since normally there
is insufficient combustible materiel topside on combatant ships to sus-
tain fire.
(However, carge ships may carry combustible deck loads, and
in special wartime conditions, even combatant ships might have com-
bustibles topside.) The most probable thermal-radiation effects are incapacitating flash burns or flash blindness among topside personnel
directly exposed to the fireball of surface bursts, topics which will
be considered in detail in Chapter 18.
Topics Considered
The free-field data and criteria necessary for assessing thermal-rad-
lation damave, and the procedure for evaluating topside thermal exposures
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