A
Geiger-Müller tube is main component of a
Geiger counter, a
radiation detection and measuring instrument. It consists of a
halogen-filled tube containing
electrodes, between which there is an electrical
voltage, but no
current flowing. When
ionizing radiation passes through the tube, a short, intense pulse of current passes "cascades" from the negative electrode to the positive electrode and is measured or counted. Most detectors include an
audio amplifier that produce an audible click on discharge. The number of pulses per
second measures the intensity of the radiation field. Some Geiger counters display a dose rate (mRh), but this is subject to error as the instrument does not discriminate between radiation at different energy levels.
Geiger-Muller tubes are of two types: the glass-mantle type and the mica window type. The glass window type will not detect alpha radiation and is usually cheaper. The mica window type will detect alpha radiation but is more fragile.
It was named for Hans Geiger and W. Müller[?], who invented it in the 1920s.