radiation+exposure

There are two major categories of radiation:
 * non-ionizing: this is the 'safe' kind of radiation, and includes visible light, infrared, microwave, and radio waves.
 * ionizing: this is the dangerous kind of radiation, which can damage living cells, and includes ultraviolet, x-rays, gamma rays, alpha and beta radiation.



You are exposed to radiation of both types every day. Here are some natural sources of ionizing radiation you may encounter:
 * the Sun emits ionizing radiation, most of which is blocked by the Earth's magnetic field; UV rays are able to pass through (some of this is blocked by the ozone layer).
 * Cosmic ionizing radiation (from space) is also mainly blocked by the Earth's magnetic field, but if you travel in airliners you get some exposure to this in the upper atmosphere.
 * medical radiology, such as x-rays, fluoroscopy, CT scans
 * trace amounts of uranium in earthen materials, from rocks to soil, to building materials like brick, concrete, cinder block, tile
 * radon gas, a decay product of uranium, that seeps into buildings from the ground (a major source of exposure).
 * radioactive fallout from nuclear weapons testing
 * radioactive waste from nuclear power plants (very low source, less than all of the above)
 * nuclear accidents (Chernobyl, Three Mile Island, Fukushima)
 * internal exposure to natural radioisotopes like carbon-14 and potassium-40.



Most radioactive isotopes will spontaneously decay through a variety of processes. These include:
 * [|alpha particle production]: the release of helium-4 from the nucleus (resulting in the loss of 4 mass units)
 * [|beta particle production]: the release of a "fast" electron from the nucleus (and conversion of a neutron to a proton)
 * [|positron production]: emission of a positron (conversion of a proton into a neutron)
 * [|electron capture] (an electron combines with a proton to form a neutron)
 * [|gamma ray emission]: release of a photon in the gamma spectrum (from an 'excited' nucleus)

Alpha radiation is actually a helium-4 nucleus, and because of its size, is easily blocked by air or paper.

Beta radiation is a fast electron released from the nucleus, and also does not travel far in air, and is easily shielded.

Gamma radiation is a high-energy, high-frequency photon (see electromagnetic spectrum) that is very powerful and is difficult to shield. It requires some dense material such as lead or concrete to effectively shield you from gamma radiation.

Radon Maps: