You've probably read about a modern type of "prospector" who goes out looking for precious metals with a Geiger counter. Or perhaps, when people are talking about the danger of atom bombs, there is mention of using Geiger counters as a safety measure.
In both cases, what is involved in the matter of radiation? Certain radioactive substances give off rays, and a Geiger counter is a simple way of detecting and measuring these rays. The Geiger counter was invented by Hans Geiger and later perfected by a man called Müller.
It is really a kind of vacuum tube. In simple terms, the tube consists of a very thin glass envelope, much like an ordinary radio tube.
Inside are two metal plates and a small amount of gas, such as argon.
You're familiar with another kind of tube that contains a gas-the neon tube. In the neon tube or lamp, the gas can be made to glow by connecting the plates to a source of electrical voltage, providing this voltage is high enough. The high voltage breaks the gas down and allows a large flow of electrons to take place between the plates. And when this flow takes place, the gas inside the tube begins to glow. In a Geiger counter, the voltage is deliberately kept too low so that the glow of the gas won't take place under normal conditions. Now, let's assume there is some radioactive substance nearby. A ray from this radioactive substance enters the tube and collides with the gas molecules. This gives them enough energy (just as higher voltage would) to cause the gas to glow.
So now there is a current surging through the tube. This current can be put through an indicating meter so that you can read the amount of radiation that has entered the tube. Or, it can be made to produce that familiar ticking sound that is associated with Geiger counters.
Since a Geiger counter is a means of detecting radiation, it obviously can't detect anything that doesn't emit rays. So its use is limited in searching for precious metals.
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