Geiger Muller tubes
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The Geiger-Müller Tube is the sensory portion of the geiger counter, which is used to detect particles of ionizing radiation. This device is named for the two scientists who helped develop it, Hans Geiger and Walther Müller.
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History
The Geiger counter was invented by Hans Geiger and Ernest Rutherford in 1908. At the time, the counter was only able to detect alpha particles. In 1928, Hans Geiger would collaborate with Walther Müller to improve the counter so that it was capable of detecting a wider range of particles. Currently, many modern modifications are still being made on the Geiger counter.
Construction
The tube is generally made out of a metal or graphite (because they are conductors), which serves the purpose of the cathode. The most common form of the tube is called an end-window tube in which one end of the tube is made of glass or mica for easier particle penetration. Mica is favored over glass because it will allow for alpha particle penetration but it is more fragile. Inside the tube is an inert gas (also known as a noble gas), generally Helium, Argon or Neon. The thin wire in the middle of the tube acts as the anode and is usually charged with several hundred volts. A counter for measuring the current is attached to the anode.
Function
When an ionizing particle penetrates through the tube, it will ionize the gas by removing electrons and creating positively charged ions. These negatively charged electrons are attracted towards the anode (the wire) and the positively charged ions are attracted towards the cathode (the walls of the tube). Along the way, further collisions will occur between atoms and electrons forming more electrons and positive ions. This gradually results in an "avalanche" effect. The counter will then begin to register the intensity of the radiation. Usually, an audio amplifier is used to produce a click for each count. The number of counts per unit time measures the intensity of the radiation.
Application to Cosmic Rays
Cosmic Rays are extremely high energy particles, usually protons, that crash into Earth’s atmosphere. The Geiger-Müller Tube is one of the classic methods for detecting cosmic rays since it is capable of detecting ionizing radiation.
