Brief introduction to RADIATION:

Any wave (e.g., sound wave, ocean wave, radio wave) is characterized by:

• amplitude
• wavelength
• velocity (speed)
• frequency

Amplitude is a familiar concept; in sound waves, it is related to the loudness of the sound. Frequency is also a familiar concept. In sound waves, it is called the pitch. High notes (sung, for example, by a soprano) correspond to rapid wave vibrations and high frequencies. Low notes (sung, for example, by a baritone) correspond to low frequencies. For example the pitch of the middle C note is 264 vibrations (cycles) per second, or 264 hertz (Hz).

We need to know three (out of four) of these properties, because frequency is the ratio of velocity and wavelength. For example, the speed of sound in air is about 300 meters per second; therefore, the wavelength of the middle C note is about 1.1 meters.

Radiation consists of special waves, which we call electromagnetic waves, whose speed is three hundred million meters per second. This is the speed of light. The frequency (and thus the wavelength) of radiation varies by many orders of magnitude.

At one extreme of this electromagnetic spectrum are the high-frequency gamma rays and x rays. These forms of radiation are produced during both controlled nuclear reactions and nuclear explosions; they are part of what we call radioactivity and can be extremely harmful. At the other extreme are the low-frequency radio and TV waves. In the middle of the range is the narrow band of 'light' or visible radiation. The radiation that reaches the Earth's surface, which comes primarily from the Sun, contains mostly visible radiation. (If the beneficial ozone layer in the upper atmosphere continues to be destroyed by human activity, increasing amounts of ultraviolet radiation will reach the Earth's surface and thus increase the incidence of skin cancer.)