Regional Basic Professional Training Course in Korea

The great utility of the G‐M tube is the result of several factors:
1. It has very high sensitivity.
2. It can be used with different types of radiation.
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2. Radiation Protection
3. It can be fabricated in a wide variety of shapes; i.e., the width can be
anywhere from 2 mm to several centimeters, and the length, 1 cm to several
meters.
4. Its output signal is so strong that it requires little or no amplification.
5. It is reasonable in cost, because the tube and the electronics following it are
extremely simple in construction.
Principles Operation
The tube itself is generally a metallic envelope in which two electrodes and a proper
filling gas are incorporated. The internal, or collector, electrode (anode) is a fine wire
(about 0.10 mm in diameter) frequently made of tungsten because of its strength and
uniformity in small‐diameter applications. The anode is most often supported at both ends
with insulators (see Fig. (2.7)). Sometimes, however, the anode is terminated at one end
by a glass bead or a loop. As opposed to ionization chambers, the most common filling
gas for a Geiger counter is one of the noble gases: helium, argon, or neon. The only
requirement is that the gas has a small electron affinity. A large range of pressures is used,
the most frequent being 9 to 50 kPa.
In other to achieve the high sensitive of the G‐M tube, a relatively high operating voltage
must be used (generally between 900 and 1200 V). Again this feature differs from that of
the ionization chamber.