Measurement of Radiation, Gas Filled Detector
Since we cannot see, smell or taste radiation, we are dependent on instruments
to indicate the presence of ionizing radiation.
The most common type of instrument is a gas filled radiation detector.
This instrument works on the principle that as radiation passes through
air or a specific gas, ionization of the molecules in the air occur. When
a high voltage is placed between two areas of the gas filled space, the
positive ions will be attracted to the negative side of the detector (the
cathode) and the free electrons will travel to the positive side (the anode).
These charges are collected by the anode and cathode which then form a very
small current in the wires going to the detector. By placing a very sensitive
current measuring device between the wires from the cathode and anode, the
small current measured and displayed as a signal. The more radiation which
enters the chamber, the more current displayed by the instrument.
Many types of gas-filled detectors exist, but the two most common are
the ion chamber used for measuring large amounts of radiation and the Geiger-Muller
or GM detector used to measure very small amounts of radiation.