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Tool for radionuclide metrology

Enhanced activity measurements by determining fundamental nuclide data

PTBnews 1.2021
Especially interesting for

radionuclide metrology

highest-resolution spectrometry

neutrino physics

nuclear medicine

Emission spectra of radionuclides can be measured with metallic magnetic calorimeters (MMCs). An MMC spectrometer was set up at PTB which allows fundamental radionuclide data to be determined with previously unachieved accuracy. These data are of paramount importance as input quantities for certain activity determination methods for the unit becquerel to be disseminated with smaller uncertainties in the form of activity standards. But the data are also important for other areas such as neutrino physics or nuclear medicine.

Comparison between the energy resolution of different detector systems (schematically for the K-X-rays of 59Co) (NaI: scintillation detector; Si(Li): semiconductor spectrometer)

Over the past 15 years, low-temperature detectors have experienced a huge technological upswing, and more and more new application fields have opened up. In this context, metallic magnetic (MMC) detectors are particularly interesting for metrological applications. Such detectors have significantly been developed at Heidelberg University. They will be increasingly gaining importance in spectrometric applications. These detectors offer excellent energy resolution while simultaneously providing high detection probability, high linearity and a low energy threshold.


One of PTB’s tasks consists in disseminating the unit becquerel in the form of activity standards. To determine activity, elaborate measurement procedures such as liquid scintillation counting are often necessary. Such methods require fundamental radionuclide input data such as the beta spectra and electron capture probabilities. Such data may have been measured or computed decades ago, but these “historic data” no longer live up to today’s accuracy requirements, which has impacts on the measurement uncertainty of the activity determination.

Within the scope of the EMPIR Metro- Beta and MetroMMC projects, an MMC spectrometer was set up at PTB. The aim was to radically improve activity measurements by determining fundamental nuclide data in collaboration with a large number of European partners. This is particularly relevant to radionuclides whose activity can be determined mainly by means of liquid scintillation methods. Especially in the case of radionuclides with low-energy emissions and without a coincident gamma transition, much lower measurement uncertainties can thus be achieved.

The data measured by means of the MMC detectors are then entered into databases with evaluated nuclide data. In this way, they allow theoretical models for a more accurate computation of spectra to be validated and improved. In addition, the data are also used by national metrology institutes for activity measurements at the highest level.

These enhanced data also benefit all users who calibrate their conventional detectors with the corresponding activity standards of PTB and are thus enabled to perform more accurate measurements themselves.


Ole Nähle
Department 6.1
Phone: +49 531 592-6110
Opens local program for sending emailole.j.naehle(at)ptb.de

Scientific publication

M. Loidl, J. Beyer, L. Bockhorn, C. Enss, S. Kempf, K. Kossert, R. Mariam, O. Nähle, M. Paulsen, P. Ranitzsch, M. Rodrigues, M. Schmidt: Beta spectrometry with metallic magnetic calorimeters in the framework of the European EMPIR project MetroBeta. Appl. Radiat. Isot. 153, 108830 (2019)