GM Tube's Dead Time
For the short amount of time the GM tube is detecting one particle, if another radioactive particle enters the tube it will not be detected. This is called dead time. The maximum dead time for our GM tube is 90 microseconds (or .00009 seconds). There is a mathematical formula for adjusting a Geiger counter read out to compensate for the GM tube's dead time. However the adjust is so small that for practical applications it can be ignored. High-end nuclear work will take a tube's dead time into consideration.
Count Rate vs. Dose Rate
Each output pulse from the GM tube is a count. The counts per second give an approximation of the strength of the radiation field. The GM tube has been calibrated using a cesium-137. The chart is shown in Figure 3.