G-M counter generater:

While a gamma generates an electron, the electron moves rapidly toward the positively charged central wire. Since the electron nears the wire, its velocity increases.  At a few point its velocity is great sufficient to cause further ionizations. As the electrons approach the central wire, the further ionizations produce a huge number of electrons in the vicinity of the middle wire.

As elaborated before, for each electron produced there is a positive ion produced.  As the applied voltage is increased then the number of positive ions nears the central wire increases and a positively charged cloud (known as a positive ion sheath) forms around the central wire.   A positive ion sheath decreases the field strength of the central wire and prevents further electrons from reaching the wire.   It might appear in which a positive ion sheath would rise the effect of the positive central wire, other than this is not true; the positive potential is applied to the extremely thin central wire which makes the strength of the electric field extremely high.  The positive ion sheath makes the central wire appear much thicker and reduces the field strength. This phenomenon is known as the detector's space charge.  It will migrate toward the negative chamber picking up electrons. Since in a proportional counter, this transfer of electrons could release energy that causing ionization and liberation of an electron. In sequence to avoid this secondary pulse, a quenching gas is used, commonly an organic compound.

The G-M counter generates many more electrons than does a proportional counter; thus, it is a much more sensitive device. It is frequently used in the detection of low-level gamma rays and beta particles for this reason. Electrons generates in a G-M tube are collected very rapidly, commonly inside a fraction of a microsecond. The outcome of the G-M detector is a pulse charge and is frequently large sufficient to drive a meter without further amplification. Since the similar size pulse is produced regardless of the amount of initial ionization, a G-M counter cannot distinguish radiation of various energies or categories. This is the reason G-M counters are not adaptable for use as neutron detectors. A G-M detector is mainly used for portable instrumentation because of its sensitivity and simple counting circuit and ability to detect low-level radiation.