Activity standards with low uncertainties are required in many disciplines such as nuclear medicine geo- and cosmochronology, industry, radiation protection and other research areas. The aim of radionuclide metrology is to develop corresponding measurements techniques, to provide activity standards for relevant radionuclides and to determine decay data such as half-lives and emission probabilities.
The Physikalisch-Technische Bundesanstalt (PTB) is the German National Metrology Institute and its “unit of activity” working group is responsible for primary activity standardization. Most frequently used techniques are based on liquid scintillation counting. In particular, the CIEMAT/NIST efficiency tracing method and the Triple-to-Double Coincidence Ratio (TDCR) method are excellent tools to measure the radioactivity of a number of radioisotopes with low uncertainties. The methods require computation of the emission spectra, e.g. the continuous energy spectrum of emitted beta electrons. In some cases, these spectra are not well known and, thus, PTB and other European institutes are going to measure beta spectra with modern cryogenic Metallic Magnetic Calorimeters (MMCs) with distinguished energy resolution.