1st 3 lines from cns 20
A Geiger counter (Geiger-Muller tube) is a device used for the detection and
measurement of all types of radiation: alpha, beta and gamma radiation. Basically
it consists of a pair of electrodes surrounded by a gas. The electrodes have a high
voltage across them. The gas used is usually Helium or Argon. When radiation
enters the tube it can ionize the gas. The ions (and electrons) are attracted to the
electrodes and an electric current is produced. A scaler counts the current pulses,
and one obtains a "count" whenever radiation ionizes the gas.
The apparatus consists of two parts, the tube and the (counter + power supply).
The Geiger-Mueller tube is usually cylindrical, with a wire down the center. The
(counter + power supply) have voltage controls and timer options.
When ionizing radiation such as an alpha, beta or gamma particle enters the tube,
it can ionize some of the gas molecules in the tube. From these ionized atoms, an
electron is knocked out of the atom, and the remaining atom is positively charged.
The high voltage in the tube produces an electric
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