A Geiger counter measures the radiation being given off by a substance. It has both a dial, giving a reading, and a loudspeaker that transmits a regular clicking sound if radiation is detected. The faster the clicking, the more radiation there is.
A Geiger counter is a metal cylinder filled with low-pressure gas sealed in by a plastic or ceramic window at one end. Running down the center of the tube there’s a thin metal wire made of tungsten. The wire is connected to a high, positive voltage so there’s a strong electric field between it and the outside tube.
When radiation enters the tube, it causes ionization, splitting gas molecules into ions and electrons. The electrons, being negatively charged, are instantly attracted by the high-voltage positive wire and as they zoom through the tube collide with more gas molecules and produce further ionization. The result is that lots of electrons suddenly arrive at the wire, producing a pulse of electricity that can be measured on a meter and (if the counter is connected to an amplifier and loudspeaker) heard as a “click.” The ions and electrons are quickly absorbed among the billions of gas molecules in the tube so the counter effectively resets itself in a fraction of a second, ready to detect more radiation. Geiger counters can detect alpha, beta, and gamma radiation.
The sound of a Geiger counter is often associated with nuclear weapons and fallout. While it is useful in these situations, it is also used every day for the detection and control of nuclear waste, by-products and exposure in nuclear power plants, hospitals and even mines.
These ingenious devices allow anyone to detect potentially harmful radiation around them, using the power of electrons and the degradation of unstable radioactive atoms.
The detector is the main part of the Geiger counter. It is responsible for capturing, detecting and then signalling that a radioactive particle, known as a radioactive isotope, has passed through the detector.
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