Draw a sketch of G.M. Counter. Explain its construction and working in detail.
Answers
When radioactive isotopes are used in medical research work particularly in human subjects it is very important that the amount of radioactive material given is as small as possible, in order that there should be minimum harmful radiations. Hence a very sensitive instrument is necessary to measure the radioactivity of materials.
Geiger and Muller developed a ‘Particle detector’ for measuring ‘ionizing radiation’ in 1928. They named it as ‘Geiger Muller Counter’. Ever since then it has been one of the most widely used nuclear detectors in the developmental days of Nuclear physics. The particle detector developed by Geiger and Muller is a gas filled counter. The main difference between ‘proportional counter’ and ‘Geiger-Muller Counter’ is in the formation of the avalanche. In the proportional counter, the avalanche is formed only at a point whereas in Geiger-Muller Counter it is formed in the central wire. Therefore, in GM Counter amplification is independent of initial ionization produced by the ionizing particle.
Geiger counter is also called as Geiger tube. This instrument is actually used for detecting and measuring ionizing radiation like alpha particles, beta particles, and gamma rays. A Geiger-Müller counter can count individual particles at rates up to about 10,000 per second and is used widely in medicine and in prospecting for radioactive ores.