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Radiation is any form of energy that is released in the form of subatomic particles or waves (also known as radiant energy). There are many different types of radiation that have a range of energy forming an electromagnetic spectrum.

Radiation has always been present in the environment and is found by natural sources such as solar radiation, radioactive elements in rocks, and even organisms. The term is often used to refer to the transfer of heat in the form of electromagnetic waves from one surface to another. For example, energy from the sun reaches the earth by radiation, and an organisms can lose heat in a similar manner. Industrial uses of radiation include microwaves, radar, electrical power lines, cellular phones, nuclear power, nuclear weapons, and medicine.

Radiation can be classified as ionizing or non-ionizing radiation, depending on its effect on atomic matter. The most common use of the word "radiation" refers to ionizing radiation, which has enough energy to break chemical bonds in molecules or remove tightly bound electrons from atoms, thus creating charged molecules or atoms (ions).[1]


Main Article: Radioactive decay

Nuclear radiation is the result of radioactive decay of atoma (also called radioactivity). This property of some atoms causes them to spontaneously give off energy as particles or rays. Radioactive atoms emit ionizing radiation when they decay, meaning they have enough energy to break chemical bonds in molecules or remove tightly bound electrons from atoms, thus creating charged molecules or atoms (ions).[2]

History of discovery

Radioactivity was first discovered by accident in 1896 by a French scientist, Henri Becquerel. He was experimenting with fluorescent and phosphorescent materials to help understand the properties of x-rays and their ability to expose photographic film, which had been discovered in 1895 by Wilhelm Roentgen. Upon seeing x-ray exposed film, he immediately thought of putting some phosphorescent rocks on photographic paper to see if it would darken the film in the same way.[3] As Becquerel had anticipated, the phosphorescent salts produced an image on the film, but he was surprised to also find a strong and clear image when the rocks were not exposed to sun. During this fortuitous sequence of events Becquerel had discovered radioactivity.[4]

Marie Curie, who was one of Becquerel's students and her husband Pierre, continued to study radiation while working in Becquerel's lab. Henri Becquerel, Marie and Pierre Curie jointly received the Nobel Prize in physics in 1903 for their discovery of radioactivity and their other contributions in this area.[5]


There are three main types of ionizing radiation known as alpha, beta, and gamma. Alpha particles are helium nuclei that have been emitted from a radioactive source. They have 2 protons and 2 neutrons and a 2+ charge. There are 3 types of Beta decay: electron emission, electron capture, and positron emission. During electron emission, a neutron changes into a proton with the loss of an electron. A gamma ray is a high-energy photon emitted by a radioisotope. Sometimes, nuclei emit gamma rays with alpha or beta particles during radioactive decay.[6]

Property Alpha radiation Beta radiation Gamma radiation
Composition Alpha particle (helium nucleus) Beta particle (electron) High-energy electromagnetic radiation
Symbol 42He or α 0-1e or β γ
Charge 2+ 1- 0
Mass 4 1/1837 0
Penetrating power Low Moderate Very high



EM Spectrum.jpg

Solar radiation is a general term for the electromagnetic radiation emitted by the sun. We can capture and convert solar radiation into useful forms of energy, such as heat and electricity, using a variety of technologies.[8]


  1. Radiation and Radioactivity by the U.S. Environmental Protection Agency.
  2. Radiation and Radioactivity by the U.S. Environmental Protection Agency
  3. Discovery of Radioactivity by Dr. V B Kamble. Vigyan Prasar Science Portal
  4. The Discovery of Radioactivity by the Lawrence Berkeley National Laboratory
  5. The Discovery of Radioactivity by Duke University Department of Chemistry.
  6. Radioactive Decay The Bodner Group. Bodner Research Web.
  7. Antony Wilbraham, et. al. Chemistry. Upper Saddle River, New Jersey: Prentice Hall, 2008. p801
  8. Solar Radiation Basics U.S. Department of Energy. Accessed July 25, 2010.

See Also