PAOLO KOCH / SCIENCE PHOTO LIBRARY PAOLO KOCH / SCIENCE PHOTO LIBRARY
Geiger counter. A geologist uses a Geiger counter to measure the amount of radioactivity produced by a natural rock formation. Natural (background) radioactivity results from the decay of the element uranium, which is present in almost all rocks and soils. When uranium decays it produces the radioactive gas radon, which issues continuously from the ground and dissipates in the open air. The reading taken from the Geiger counter can be used to identify the different types of rock in the vicinity.
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