Question

Why is the GM detector not capable of discriminating between different forms of radiation?

Answer 1

G. M. Detector is a gas based detector which uses ionization of gas by radiation as the primary

tool to detect radiation. The tube is in the form of cylinder and is filled up with noble gas at certain

low pressure. A metallic string which runs through the central axis of the cylindrical shape forms the

anode whereas the outer shell serves as cathode. One end of the tube has radiation permeable window

( mica or beryllium ).

Any radiation incident on the tube window will ionize the noble gas. The electrons thus ejected

will get attracted towards the anode whereas the heavy ions will move slowly towards cathode. These

charges will further ionize more number of atoms thereby setting up an avalanche of ions and electrons

which sets up a discharge current. The current causes the voltage between the anode and cathode to

drop which the counter detects as a signal.

Since the detection is based on the avalanche, therefore the output pulses are independent of the en-

ergy brought in by the incident radiation The pulse height remains the same irrespective of the energy

of radiation and therefore GM counter can only be used to detect the presence of radiation but not the

type of radiation.so that is the reason G. M. Detector is not capable of discriminatin6 between different forms of radiation.