Dead time:

Electrons being lighter travel faster and form a sheath around the anode wire compared to positively charged ions that are heavy and not able to reach the cathode wall so fast. This efficiently lowers the potential gradient to point whereas the counter becomes insensitive to incoming radiations. A time period for that the counter does not respond to the further incoming radiation is known dead time or paralysis time.  During this time, the counter is not able to resolve among two successive radiations reaching the counter thus affecting its sensitivity. As an output, observed count rate (m) becomes less than the true count rate (n) and is correlated as.

n = m/1 - mτ

where, τ is the dead time of the detector system and is of the order of 100 to 500 µs. It may be determined experimentally.