4
Statistics of Radiation Counting
34
As mentioned in previous chapters, radioactive decay is a random process,
and therefore one can expect fluctuations in the measurement of radioac-
tivity. The detailed discussion of the statistical treatment of radioactive mea-
surements is beyond the scope of this book. Only the salient points of
statistics related to radiation counting are given here.
Error, Accuracy, and Precision
In the measurement of any quantity, an error in or deviation from the true
value is likely to occur. Errors can be two types:systematic and random.
Systematic errors appear as constant deviations and arise from malfunc-
tioning instruments and inappropriate experimental conditions. These
errors can be eliminated by rectifying the incorrect situations. Random
errors are variable deviations and arise from the fluctuations in experi-
mental conditions such as high-voltage fluctuations or statistical fluctua-
tions in a quantity such as radioactive decay.
The accuracyof a measurement of a quantity indicates how closely it
agrees with the “true” value. The precisionof a series of measurements
describes the reproducibility of the measurement, although the measure-
ments may differ from the “average” or “mean” value. The closer the
measurement is to the average value, the higher the precision, whereas
the closer the measurement is to the true value, the more accurate the
measurement. Remember that a series of measurements may be quite
precise, but their average value may be far from the true value (i.e., less
accurate). Precision can be improved by eliminating the random errors,
whereas better accuracy is obtained by removing both the random and
systematic errors.