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10 Physical Effects of Nuclear Weapons
Each of these effects (blast, thermal, and radiological) will be discussed for
weapons detonated at the surface and in the air.
10.1 Characteristics of a Nuclear Explosion
At the moment of detonation a nuclear weapon heats the material surrounding it
to temperatures high enough to vaporize most known materials and to heat the air
and vapor to incandescence. This roughly spherical volume is the fireball and it can
be from a few hundred meters to a few km in radius depending on the weapon’s
yield. The energy absorbed by the air causes the expansion of the air that powers the
blast wave; this is about 40% of the energy from fission. The remaining 35–45% of
the fission energy is emitted in the form of thermal radiation that is deposited at a
distance from the detonation.
10.1.1 Blast Effects
A moment after the fission reaction occurs the energy released heats the bomb and the
air immediately surrounding it to temperatures of several tens of millions of degrees.
This temperature is hot enough to vaporize any known materials. The resulting expansion of the air and vapors causes pressures to momentarily reach as much as a few
million atmospheres before the gas begins to expand [1]. It is this initial release
of energy, the heat it deposits, and the initial pressure it causes that initiates the
destructive blast wave that radiates out from the site of the explosion.
As the heated air expands it forms a shock wave that rushes outwards from the
point of detonation at high speed. The shock wave is initially supersonic but drops to
sonic speeds within several tens of seconds. Initially, there may be two shock waves,
the primary shock from the detonation itself as well as a secondary shock that is
reflected from the ground in the event of an air burst; these merge within a few km
to form a consolidated shock wave called the Mach front that propagates outwards.
The strength of the blast wave depends on the distance from the fireball, dropping
in strength as it grows in area. Thus, a shock that is able to collapse a masonry
structure at a distance of one km and that can kill a person through blast injuries at a
distance of three or four km will only be able to break glass at a distance of ten km.
The effects of this blast will be largely the same in nature, although much greater
in magnitude than those noted in Chap. 7. Broken glass, for example, can occur as
far away as 4 km from the site of the detonation of a 10 kt explosion, affecting more
than one million people in a densely populated city such as New York City. Closer
in, buildings would likely be completely destroyed to a distance of 300 m and would
be severely damaged to a distance of 1 km away [1]. This would affect more than a
half million people in a densely populated city.
10 Physical Effects of Nuclear Weapons
Each of these effects (blast, thermal, and radiological) will be discussed for
weapons detonated at the surface and in the air.
10.1 Characteristics of a Nuclear Explosion
At the moment of detonation a nuclear weapon heats the material surrounding it
to temperatures high enough to vaporize most known materials and to heat the air
and vapor to incandescence. This roughly spherical volume is the fireball and it can
be from a few hundred meters to a few km in radius depending on the weapon’s
yield. The energy absorbed by the air causes the expansion of the air that powers the
blast wave; this is about 40% of the energy from fission. The remaining 35–45% of
the fission energy is emitted in the form of thermal radiation that is deposited at a
distance from the detonation.
10.1.1 Blast Effects
A moment after the fission reaction occurs the energy released heats the bomb and the
air immediately surrounding it to temperatures of several tens of millions of degrees.
This temperature is hot enough to vaporize any known materials. The resulting expansion of the air and vapors causes pressures to momentarily reach as much as a few
million atmospheres before the gas begins to expand [1]. It is this initial release
of energy, the heat it deposits, and the initial pressure it causes that initiates the
destructive blast wave that radiates out from the site of the explosion.
As the heated air expands it forms a shock wave that rushes outwards from the
point of detonation at high speed. The shock wave is initially supersonic but drops to
sonic speeds within several tens of seconds. Initially, there may be two shock waves,
the primary shock from the detonation itself as well as a secondary shock that is
reflected from the ground in the event of an air burst; these merge within a few km
to form a consolidated shock wave called the Mach front that propagates outwards.
The strength of the blast wave depends on the distance from the fireball, dropping
in strength as it grows in area. Thus, a shock that is able to collapse a masonry
structure at a distance of one km and that can kill a person through blast injuries at a
distance of three or four km will only be able to break glass at a distance of ten km.
The effects of this blast will be largely the same in nature, although much greater
in magnitude than those noted in Chap. 7. Broken glass, for example, can occur as
far away as 4 km from the site of the detonation of a 10 kt explosion, affecting more
than one million people in a densely populated city such as New York City. Closer
in, buildings would likely be completely destroyed to a distance of 300 m and would
be severely damaged to a distance of 1 km away [1]. This would affect more than a
half million people in a densely populated city.