Marcell Takacs (PTB Braunschweig): Radionuclide metrology: Absolute measurement of activity

Radioactive reference sources are commonly used to calibrate detectors for ionizing radiations. In most cases, the detection efficiency for a specific measuring geometry is deduced based on the counting rate registered by the detector and the quoted activity of the radioactive standard. This requirement for reference sources with precisely known activities, however, leaves one with a puzzling dilemma: if it is not feasible to calibrate a detector without them, how is it still possible to measure the activity of these primary standards?

To answer this question, the present talk provides an insight into the various absolute measurement methods and experimental techniques used at the Physikalisch-Technische Bundesanstalt (PTB) to realize the unit of activity, the Bequerel (Bq).