Interpretation of the peak areas in gamma-ray spectra that have a large relative uncertainty

Empirical evidence is provided that the areas of peaks having a relative uncertainty in excess of 30% are overestimated. This systematic influence is of a statistical nature and originates in way the peak-analyzing routine recognizes the small peaks. It is not easy to detect this influence since it is smaller than the peak-area uncertainty. However, the systematic influence can be revealed in repeated measurements under the same experimental conditions, e.g., in background measurements. To evaluate the systematic influence, background measurements were analyzed with the peak-analyzing procedure described by Korun et al. (2008). The magnitude of the influence depends on the relative uncertainty of the peak area and may amount, in the conditions used in the peak analysis, to a factor of 5 at relative uncertainties exceeding 60%. From the measurements, the probability for type-II errors, as a function of the relative uncertainty of the peak area, was extracted. This probability is near zero below an uncertainty of 30% and rises to 90% at uncertainties exceeding 50%.

► A systematic influence affecting small peak areas in gamma-ray spectra is described.
► The influence originates in the peak locating procedure, using a pre-determined sensitivity.
► The predetermined sensitivity makes peak areas with large uncertainties to be overestimated.
► The influence depends on the relative uncertainty of the number of counts in the peak.
► Corrections exceeding a factor of 3 are attained at peak area uncertainties exceeding 60%.