Fallout shelter
A fallout shelter is an enclosed space specially designated to protect occupants from radioactive debris or fallout resulting from a nuclear explosion. Many such shelters were constructed as civil defense measures during the Cold War.
For the 2015 video game, see Fallout Shelter. For the Island Records studio known as The Fallout Shelter, see 22 St Peter's Square.
During a nuclear explosion, matter vaporized in the resulting fireball is exposed to neutrons from the explosion, absorbs them, and becomes radioactive. When this material condenses in the rain, it forms dust and light sandy materials that resemble ground pumice. The fallout emits alpha and beta particles, as well as gamma rays.
Much of this highly radioactive material falls to Earth, subjecting anything within the line of sight to radiation, becoming a significant hazard. A fallout shelter is designed to allow its occupants to minimize exposure to harmful fallout until radioactivity has decayed to a safer level, over a few weeks or months.
A fallout shelter is designed to protect its occupants from:
Different types of radiation emitted by fallout[edit]
Alpha (α)[edit]
In the vast majority of accidents, and in all atomic bomb blasts, the threat due to beta and gamma emitters is greater than that posed by the alpha emitters in the fallout. Alpha particles are identical to a helium-4 nucleus (two protons and two neutrons), and travel at speeds in excess of 5% of the speed of light. Alpha particles have little penetrating power; most cannot penetrate through human skin. Avoiding direct exposure with fallout particles will prevent injury from alpha radiation.[42]
Beta (β)[edit]
Beta radiation consists of particles (high-speed electrons) given off by some fallout. Most beta particles cannot penetrate more than about 3 metres (10 ft) of air or about 3 mm (1⁄8 in) of water, wood, or human body tissue; or a sheet of aluminum foil. Avoiding direct exposure with fallout particles will prevent most injuries from beta radiation.[43]
The primary dangers associated with beta radiation are internal exposure from ingested fallout particles and beta burns from fallout particles no more than a few days old. Beta burns can result from contact with highly radioactive particles on bare skin; ordinary clothing separating fresh fallout particles from the skin can provide significant shielding.[43]
Gamma (γ)[edit]
Gamma radiation penetrates further through matter than alpha or beta radiation. Most of the design of a typical fallout shelter is intended to protect against gamma rays. Gamma rays are better absorbed by materials with high atomic numbers and high density, although neither effect is important compared to the total mass per area in the path of the gamma ray. Thus, lead is only modestly better as a gamma shield than an equal mass of another shielding material such as aluminum, concrete, water or soil.
Some gamma radiation from fallout will penetrate into even the best shelters. However, the radiation dose received while inside a shelter can be significantly reduced with proper shielding. Ten halving thicknesses of a given material can reduce gamma exposure to less than 1⁄1000 of unshielded exposure.[44]
Weapons versus nuclear accident fallout[edit]
The bulk of the radioactivity in nuclear accident fallout is more long-lived than that in weapons fallout. A good table of the nuclides, such as that provided by the Korean Atomic Energy Research Institute, includes the fission yields of the different nuclides. From this data it is possible to calculate the isotopic mixture in the fallout (due to fission products in bomb fallout).