'''Gamma rays''' (often denoted by the Greek letter gamma, γ) are an energetic form of
electromagnetic radiation produced by
radioactive decay or other nuclear or subatomic processes such as
electron-positron annihilation.
Gamma rays form the highest-energy end of the electromagnetic spectrum. They are often defined to begin at an energy of 10 keV, corresponding to a minimum frequency of 2.42 EHz, or a maximum wavelength of 124 pm, although electromagnetic radiation from around 10 keV to several hundred keV is also referred to as hard
x-rays. It is important to note that there is no physical difference between gamma rays and X-rays of the same energy — they are two names for the same electromagnetic radiation, just as sunlight and moonlight are two names for visible light. Rather, gamma rays are distinguished from X-rays by their origin. ''Gamma ray'' is a term for high-energy electromagnetic radiation produced by nuclear transitions, while ''X-ray'' is a term for high-energy electromagnetic radiation produced by energy transitions due to accelerating electrons. Because it is possible for some electron transitions to be of higher energy than some nuclear transitions, there is an overlap between what we call low energy gamma rays and high energy X-rays.
Gamma rays are a form of
ionizing radiation; they are more penetrating than either
alpha or
beta radiation (neither of which is electromagnetic radiation), but less ionizing. For instance, a gamma ray will pass through 1 cm of aluminium, while an alpha ray will be stopped by even a single sheet of paper.
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Last modified: 13.09.07 by jross
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