Statistics of count numbers from a photomultiplier tube and its implications for error estimation

We present investigations of counting statistics for five different luminescence-measuring systems. The dark current background and the counts obtained for a PM tube under constant illumination at various light intensities were measured. Where no divider is present in the counting system, the standard deviation of the number of counts exceeds the value predicted by a Poisson distribution but by different amounts in the different systems. This has implications for analysis of the uncertainties in the estimated equivalent doses and other quantitative analyses of luminescence measurements. We suggest how to account for the observed overdispersion of count numbers in uncertainty estimation.

► We investigate the scatter of count numbers registered by PM tube systems.
► The scatter exceeds the one of a Poisson distribution.
► Uncertainties of count numbers should be multiplied by a correcting factor.
► The correcting factor must be determined for each system individually.