Effectiveness of time and digital versions of radiometry when detecting sources of ionizing radiation

Abstract

In radiometric practice, experiments to detect sources of ionizing radiation with random time characteristics are usually carried out in two ways, in which sliding filtering of the data at m fixed intervals is used: 1) the time interval t o is fixed, and the filter is organized for the number of readouts k in the time t o (henceforth called the "digital" version of radiometry), and 2) the range of numbers k 0 is fixed, and the filter is organized for time intervals t, during which k 0 successive readouts occur (henceforth called the "time" version) [1-3]. It is usually stated that both versions are equivalent, but the conclusion is drawn in [2] that the second version is preferable, since, in the authors' opinion it provides better time resolution for the same detection efficiency, i.e., for an equal level of significance and power of the criterion [4] for background-signal classification. Nevertheless, there are indications in the same papers that there are differences in the conclusions when processing data using one version or another, for example, in the standard problem of determining the intensity of the readouts in the detector. These differences are as follows [1-3]. Suppose At is the mean intensity of the readouts (henceforth assumed to be constant and known when considering the mode of detection) in the detector (for the background intensity mode of detection), and T is the mean intensity of the readouts for the signal; the half-life of radioactive elements considerably exceeds the measurement time. Then, in the first version, the distribution k of the readouts during the time t o has a Poisson distribution: