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It is generally known that gamma radiation is quite
similar to light waves in its passage through the atmosphere, but possessing much greater
energy, it is able to penetrate gases, liquids, and solids with comparative ease. In
passing through air, a gamma ray will collide with many air molecules, thereby losing
small amounts of its energy with each collision.
The energy imparted to any one molecule is usually sufficient to
result in the formation of two oppositely charged particles (ionization)· Being
oppositely charged, the particles would be attracted to each other to form a neutral
molecule again, if the particles were not influenced by an electric field. However, if the
charged particles formed by the gamma ray are located in an electric field, each particle
could be attracted to a charged surface of opposite polarity and be
neutralized.
The polarity of these surfaces is established by charging them with
a D.C. voltage. As the charged air particles become neutralized by contact with oppositely
charged surfaces, the voltage between these surfaces is reduced. This decrease in surface
voltages directly proportional to the total amount of ionizing radiation to which the air
has been subjected.
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