Geoscience Reference
In-Depth Information
X-rays, only more powerful, more penetrating, and more destructive to living tissues. Gamma
rays are the most immediately damaging form of radiation, and are what the thick dense walls
of fallout shelters are specifically designed to block.
The second and third types of radiation are alpha and beta particles. Radioactive debris,
such as nuclear-blast “fallout,” emits gamma rays, alpha particles, and beta particles. Beta
particles are simply free-flying high-energy electrons, which can penetrate light clothing or
about ⅛ inch of flesh, causing surface “beta burns” when radioactive fallout is left on the skin
for more than a few minutes. Alpha particles don't have much penetrating power, being
stopped by skin and clothing, so they don't pose much of a threat unless they are emitted by ra-
dioactive particles that have been ingested and become lodged in organs of the body, where
over time they may contribute to cancerous growths and tumors.
“Fallout” is composed of small radioactive particles resulting from a nuclear detonation, or
the release of airborne radioactive debris from a damaged nuclear reactor, or the explosion of a
dirty bomb. In the case of a ground or low-altitude burst, thousands of tons of these particles
are carried far into the atmosphere by the classic mushroom cloud of a nuclear blast. The heav-
ier of these particles tend to settle out of the air fairly quickly, and may look like grains of rice,
salt, ash, or fall as “black rain.” Tiny microscopic particles of fallout may stay airborne for
weeks, traveling many thousands of miles while floating on air currents. The most highly radio-
active components in the fallout from a nuclear detonation decay quite quickly, so the more
time that elapses from the moment of detonation, the less radioactive the fallout becomes, re-
gardless of whether it is in the air, on the ground, or in the water. The longer fallout particles
remain in the air before settling to the ground, the less radioactive they will be when they hit
