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The word “radiation” might make you think of science-fiction movies, mutants, or the Incredible Hulk. The truth is radiation exists naturally all around us and is part of our everyday lives. Radiation is the emission of energy as electromagnetic waves or as moving subatomic particles. Basically, it is the way energy moves from one place to another. Radiation has a wide range of energies that form the electromagnetic spectrum.


Light is a mixture of colors. White light can be dispersed into its component colors: violet, indigo, blue, green, yellow, orange, and red. This ordered arrangement of colors is called the visible spectrum (a rainbow). A particular color of light can be specified by either its frequency or its wavelength with the property that the frequency multiplied by the wavelength is equal to the speed of light, about 300 million meters per second (about 186,000 miles per second).


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During the 19th century, scientists discovered that beyond the violet end of the spectrum, radiation could be detected that was invisible to the human eye but that had marked photochemical action; this radiation was termed ultraviolet. Similarly, beyond the red end of the spectrum, infrared radiation was detected that, although invisible, transmitted energy, as shown by their ability to raise the temperature of a thermometer. The definition of spectrum was then revised to include this invisible radiation, and has since been extended to include microwaves and radio waves beyond the infrared, and X-rays and gamma rays beyond the ultraviolet.

The spectrum has two major divisions:

Non-ionizing radiation - Radiation that has enough energy to move around atoms in a molecule or cause them to vibrate, but not enough to remove electrons, is referred to as non-ionizing radiation.

We take advantage of the properties of non-ionizing radiation in everyday tasks:

Ionizing Radiation - Radiation that has enough energy to remove tightly bound electrons from atoms, thus creating ions is referred to as ionizing radiation. This is the type of radiation that people usually think of as “radiation.” We take advantage of its properties to generate electric power, to kill cancer cells, and in many manufacturing processes.

There are three main kinds of ionizing radiation:

Alpha Particles

Alpha particles are composed of two protons and two neutrons emitted from an unstable atom. They travel at approximately 36 million miles per hour (16,000 kilometers per second)

Beta Particles

Beta particles are high-energy (high-speed) electrons that have been emitted by an unstable atom. They have almost no mass and travel at approximately 560 million miles per hour (250,000 kilometers per second). They penetrate farther than the relatively heavy alpha particles

Gamma Rays

Gamma rays are quanta (pulses) of high energy emitted from an unstable atom. They are pure energy (photons). They travel at the speed of light (300,000 kilometers per second) and are continually reduced in intensity with distance of penetration.

Additional reading

How Radiation Isn’t Killing You : Discovery News (Oct 2013)

Daily ultraviolet radiation doses from sunlight vary by latitude and season. Credit: NOAA

Daily ultraviolet radiation doses from sunlight vary by latitude and season. Credit: NOAA

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