2. Depth of burst
radiation increases because line-of-sight area
increases, and there are fewer shadows from such
3. Depth of water
things as existing structures, vegetation, and terrain
4. Bottom configuration and structure
features.
When the point of detonation is above the bottom,
As the weapon yield is increased, the range at
the shock wave reflected from the bottom can produce
which thermal radiation can cause skin burns and eye
more severe damage to weapon-delivery equipment at
injuries to exposed personnel increases. It will extend
a given range than the direct shock wave. Even though
well beyond the range at which blast and initial nuclear
the peak pressure of the reflected wave is less than that
radiation are of significance. The emission rate of
of the direct wave, the reflected wave will disperse in a
thermal radiation from a high-yield weapon is slower
more nearly vertical direction. It is, therefore, more
than that from a low-yield weapon. Thus the high-yield
effective in producing the vertical motions that control
weapon must deliver more thermal energy to do an
the degree of damage.
equivalent amount of damage because a target has
more time to dissipate the heat being received.
The time separation between direct and reflected
shock waves decreases as the point of detonation
The ability of the atmosphere to lessen the effect of
approaches the bottom. When the point of detonation is
thermal radiation depends on such factors as
directly on the bottom, the two waves overlap. For such
absorption by water vapor, carbon dioxide, ozone, and
a burst, the water depth has a direct effect on the range
impurities in the air. On days when fog, haze, and
at which the weapon-delivery capability of surface
clouds are between the point of detonation and the
ships will be impaired. However, the water depth has
target, thermal radiation will be decreased. On the
no significant effect on the ranges at which their
other hand, when fog, haze, and clouds are above the
mobility and seaworthiness will be impaired. Where
burst and the target, a significant amount of thermal
the sea bottom is sloped, a ship downslope from the
radiation will reflect downward and increase the
point of detonation will tend to receive less damage
severity of burns received at a given location. Such
than a ship an equal distance upslope from the point of
conditions can also increase the number of personnel
detonation. Where the sea bottom is essentially flat, the
who are flash-blinded or dazzled by a burst. The terrain
strength of a reflected wave will depend on the bottom
surface cover, such as snow, can also reflect significant
structure. It will be less for mud than for sand, but
thermal radiation. This adds to both the range and
greater for rock than for sand.
severity of the thermal effect.
THERMAL RADIATION
NUCLEAR RADIATION
Thermal radiation is the radiant energy (heat and
The four types of nuclear radiation released as the
light) that is emitted by the fireball. Thermal radiation
result of a nuclear explosion are alpha particles, beta
travels at the speed of light and persists as long as the
particles, gamma rays, and neutrons.
fireball is luminous. The duration of thermal radiation
emission depends on weapon yield. It will last less than
Alpha particles travel only a few centimeters in air
1 second for a weapon yield of l KT and approximately
before they are stopped. They cannot penetrate even a
8 or 9 seconds for a weapon yield of l MT. Thermal
thin sheet of paper.
radiation is effectively shielded by anything that will
Beta particles can travel several feet in air, but they
cast a shadow (opaque materials). Thermal radiation
cannot penetrate a sheet of aluminum that is more than
can incapacitate exposed personnel by causing skin
a few millimeters in thickness. Beta particles cannot
burns, flash blindness, or retinal burns.
penetrate the normal combat uniform.
Over land, thermal radiation will ignite fires in
Gamma rays are a form of electromagnetic
bu i l d i n g s , ve h i c l e s , d r y veg e t a t i o n , a n d o t h e r
radiation, indistinguishable from X rays.
combustible materials.
Neutrons are electrically neutral particles. Both
Thermal radiation is modified by the height of the
gamma rays and neutrons can travel great distances in
point of detonation, weapon yield, atmospheric
air. Gamma rays and neutrons have greater penetrating
conditions, cloud cover, and terrain features. As the
power than the other forms of nuclear radiation. Their
height of the point of detonation is increased, the area
injurious effects on personnel are also quite similar.
of the surface of the earth exposed to the thermal
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