A simple graphical method to evaluate deadtime and countrate losses

The conventional method to evaluate the deadtime and countrate losses of scintillation counters often overestimates these performance parameters. This is caused by the fact that no countrate can be measured without losses. Therefore expected countrates are incorrect. This overestimation of system performance is of some importance for the clinical use of cameras, as scattered radiation from the patient decreases the ideal values deduced from measurements in air. Correct performance parameters can be calculated from 'relative countrates', i.e. the ratio of measured countrate over activity in arbitrary units. This ratio is drawn graphically on a logarithmic scale against activity. The monotonous curve yields the deadtime and 10% (20%) countrate loss unambiguously. The evaluation is independant of any deadtime concept or of the individual countrate loss or defective measurements. (orig.)