Radiation Exposure

The word radiation refers to two closely related things. First, it refers to forms of radiant energy, particularly that represented by subatomic particles (for example, the type of radiation released during a nuclear explosion), and by electromagnetism (for example, the type of radiation emitted by a light bulb, and by the sun). Sound is also considered a type of radiation.

The word radiation can also refer to the release and propagation through space of the energy itself. For example, a block of uranium releases radiation in the form of radioactive particles. Both the release of the particles, and the particles themselves, are called radiation. However, not all radiation is radioactive. The particle radiation released from uranium is radioactive, but the electromagnetic radiation emitted by a light bulb is not. Radioactivity is a form of radiation which involves the release of alpha particles, neutrons, electrons, and gamma rays, emitted by radioactive elements and substances.

Most of the radiation on the earth's surface is electromagnetic radiation, which travels in waves of different frequency. (Frequency is the number of waves passing a point each second; it is the inverse of wavelength.) From the lowest to highest frequency, the spectrum of electro-magnetic radiation is divided into the following ranges: radio waves, microwaves, visible light, ultraviolet light, x rays, and gamma rays. Visible light can be detected by the human eye, and is divided into the following color ranges: red, orange, yellow, green, blue, violet (arranged from lowest to highest frequency).

Sound, or acoustic radiation is also classified according to its frequency. In increasing order of frequency, sound radiation is classified as infrasonic, sonic, and ultrasonic.