Count-rate

Count-rate is different: it is the number of events recorded each second by a detector, such as a Geiger–Müller tube. The recorded count-rate need not equal the activity. Some emitted radiation travels away from the detector, may be absorbed before reaching it or may not be detected.

Take several readings over equal time intervals and calculate their mean to obtain a more representative background count rate.

A half-life graph plots activity, count rate or number of undecayed nuclei on the vertical axis against time on the horizontal axis. It slopes downwards and curves because equal time intervals produce equal fractional decreases rather than equal numerical decreases.