Short Time Delays in Geiger Counters

Abstract

There are at least two types of short time delays in the firing of Geiger counters. The first is due to the transit time of the secondary electrons as they migrate toward the central wire. This time can be measured when beta particles are sent parallel to the axis of the counter, creating secondaries at known distances from the axis. In a typical counter, 2.2 cm in diameter, the maximum secondary electron transit time is measured at about 11×10−8 second. The second delay occurs between the time the electron arrives near the center wire, and the time a pulse is detected on the output of a wide band amplifier connected to the center wire. Increasing the voltage on the counter from the threshold to an over-voltage of 250 volts, decreases this delay by 10 to 20×10−8 second. It is suggested that this delay is due to the time required to form the initial part of the ion sheath.