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The American Experience
Effects of a Nuclear Explosion


Damage caused by nuclear explosions can vary greatly, depending on the weapon's yield (measured in kilotons or megatons), the type of nuclear fuel used, the design of the device, whether it's exploded in the air or at earth's surface, the geography surrounding the target, whether it's winter or summer, hazy or clear, night or day, windy or calm. Whatever the factors, though, the explosion will release several distinct forms of energy. One form is the explosive blast. Other forms are direct nuclear radiation and thermal radiation. And then there's radioactive fallout -- not exactly energy released by the explosion, but still a destructive result.

photo of shock wave hitting house Explosive Blast
Much of the damage inflicted by a nuclear explosion is the result of its shock wave. There are two components to a blast's shock wave. First, there's the wall of pressure that expands outward from the explosion. It is this pressure, measured in psi (pounds per square inch), that blows away the walls from buildings. A typical two-story house subjected to 5 psi would feel the force of 180 tons on the side facing the blast. (Download the Quicktime movie entitled house to see an example of a building subjected to this type of pressure.) Additionally, the blast creates a 160 mile-an-hour wind. And that's only at 5 psi. The wind speed following a 20 psi blast would be 500 mph!

Direct Nuclear Radiation
A nuclear detonation creates several forms of nuclear, or ionizing, radiation. The nuclear fission (atom splitting) and nuclear fusion (atom combining) that occur to produce the explosion release, either directly or indirectly, neutrons, gamma rays, beta particles, and alpha particles. Neutrons are heavy particles that are released from atoms' nuclei. These tiny "missiles" can easily penetrate solid objects. Another penetrating form of radiation is gamma rays, which are energetic photons. Both of these types of radiation can be deadly. Beta and alpha particles are less dangerous, having ranges of several meters and several centimeters, respectively. Alpha particles can cause harm only if they are ingested.

Thermal Radiation
You don't have to be close to ground zero to view the bright flash created by the exploding bomb. The flash from a bomb has been viewed from hundreds of miles away. In addition to being intensely bright, this radiation is intensely hot (hence the name "thermal"). If you're seven miles away from a one megaton explosion, the heat emanating from the fireball will cause a first-degree burn (equivalent to a bad sunburn ) to any exposed skin facing the light. If you're six miles away, it will cause second-degree burns. And if you're five miles away, the thermal radiation will cause third-degree burns -- a much more serious injury that would require prompt medical attention.

The intense heat would also ignite a "mass fire" -- i.e., a fire that could cause large areas to simultaneously burst into flames.

radiation burns Fallout
You've seen the image: a mushroom cloud created by a nuclear explosion. Produced with a detonation at or near the earth's surface, this type of explosion results in far-ranging radioactive fallout. Earth and debris -- made radioactive by the nuclear explosion -- rises up, forming the mushroom cloud's stem. Much of this material falls directly back down close to ground zero within several minutes after the explosion, but some travels high into the atmosphere. This material will be dispersed over the earth during the following hours, days, months. In fact, some of the particles rising up through the mushroom will enter the stratosphere, where they could remain for tens of years.

Wind direction, naturally, plays a significant role in how the radioactive fallout will be distributed. But so does wind speed. The Blast Mapper's fallout maps show the area where fallout would land if the wind were blowing at a steady 15 mph. Lighter winds would cause this area to be broader but not so deep. A stronger breeze would cause the fallout "plume" to be narrower and longer.


See damage from another blast.

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