a device used to detect radioactive radiations, such as those given off in the release of nuclear energy

The German physicist Hans Geiger and the British scientist Sir Ernest Rutherford developed the first radiation counter in 1908. Geiger counters in use today are based on designs made by Geiger and E.W. Müller in the 1920's.

Basic Construction

A Geiger counter usually consists of a glass tube about 3/4 inch in diameter enclosing a metal cylinder, often of copper, about 4 inches long along the axis of which runs a thin metal wire, which is often of tungsten. The cylinder and wire are connected through the end wall of the glass tube to a source of electrical voltage. The tube is filled with a gas, usually argon, at a low pressure, equivalent to a pressure of a few centimeters of mercury. A voltage is set up between the cylinder (the negative electrode or cathode) and the wire (the positive electrode or anode) which is just a little less than that needed to create an electrical discharge between the two electrodes.

How It Works

When a charged particle with high energy flies through the glass tube it knocks electrons out of the atoms of the gas. These electrons, being negatively charged, make for the wire anode and the damaged atoms, which are positively charged argon ions, make for the cathode. The electrons pick up enough energy to knock more electrons out of atoms, which in turn pick up further energy and liberate even more electrons. This is known as electron avalanche. At the same time, the positive ions hit the cylinder with enough energy to release still more electrons. An avalanche of electrons therefore descends on the wire, which can be detected as a pulse of electric current, indicating that a charged particle has passed through the tube. This pulse is revealed by light signals, by clicks picked up by earphones, or by readings on a meter.

ILLUSTRATION SOURCE
The Illustrated Science and Invention Encyclopedia New York: H.S. Stuttman Co., Inc., 1977

SEE ALSO
Sir Ernest Rutherford

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This page was last updated on 05/18/2017.