Beta spectrometry with metallic magnetic calorimeters in the framework of the EU EMPIR project METROBETA

Martin Loidl (1) , J. Beyer (2) , L. Bockhorn (3) , Christian Enss (4) , S. Kempf (4) , Karsten Kossert (3) , Riham Mariam (1) , Ole Nähle (3) , M. Paulsen , P. Ranitzsch , Matias Rodrigues (1) , M. Schmidt (2)

1 LNHB (CEA, LIST) - Laboratoire National Henri Becquerel (CEA, LIST)
2 PTB - Physikalisch-Technische Bundesanstalt [Berlin]
3 PTB - Physikalisch-Technische Bundesanstalt [Braunschweig]
4 Kirchhoff Institut für Physik

MetroBeta is a European EMPIR (European Metrology Programme for Innovation and Research) project aiming at the improvement of the knowledge of the shapes of beta spectra, both in terms of theoretical calculation and measurement. In this context, metallic magnetic calorimeters (MMCs), cryogenic detectors operated at very low temperature (below 20 mK), have been developed for the precise measurement of the shapes of beta spectra. MMCs with the beta emitter embedded in a metallic particle absorber has already proven to be among the best beta spectrometers, in particular for low energy beta transitions. Since the MMCs must be designed specifically to match the absorber heat capacity for optimal energy sensitivity, within this project several MMC designs have been optimized for the absorber sizes required for the measurement of beta spectra with Q values ranging from a few tens of keV up to ~ 1 MeV. Four spectra from mostly pure beta emitters will be measured within the project: Sm-151 (Q = 76.3 keV, the only one of the radionuclides having a small beta decay branch to an excited state), C-14 (Q = 156.5 keV), Tc-99 (Q = 293.8 keV) and Cl-36 (Q = 709.5 keV). Intense research and development work was devoted to the fabrication of high quality sources for each of the radionuclides and their integration within the MMC absorbers. This particular study is of utmost importance since previously it had been observed that the spectra measured with sources composed of a salt can be considerably distorted due to the loss of a fraction of the beta energy in the salt which is then not fully converted to heat. Another study concerning the composition of the absorbers is still ongoing. For low energy spectra, simple gold or silver absorbers can be used. However, spectra with Q values higher than ~ 500 keV can be distorted by the escape of Bremsstrahlung from the absorber. Monte Carlo simulations were performed to study the influence of the absorber material and the usefulness of composite absorbers to minimize this source of spectrum distortion. A series of measurements is currently under preparation to explore the optimum source-absorber configuration for the beta spectrum of Cl-36. he comparison of the measured spectra with the theoretical spectra calculated with the advanced code BetaShape, which is being further developed within the project, will be presented.

Mots clés: Tc-99; Cl-36; C-14; beta spectra; metallic magnetic calorimeter; detection efficiency; beta source; shape factor; beta spectrum; beta radionuclide; metrology; cryogenic detector; Sm-151; spectrum measurement; 63Ni; NiCl2 solution; electroplated source; atomic exchange; Beta spectrometry; Ionizing radiation; Nuclear data

Domaines: Instrumentations et Détecteurs [physics.ins-det]; Physique Nucléaire Expérimentale [nucl-ex]

Martin Loidl, J. Beyer, L. Bockhorn, Christian Enss, S. Kempf, et al.. Beta spectrometry with metallic magnetic calorimeters in the framework of the EU EMPIR project METROBETA. 22nd International Conference on Radionuclide Metrology and its Applications (ICRM 2019), Laboratorio de Radiaciones Ionizantes - Datación Universidad de Salamanca, May 2019, Salamanca, Spain. pp.187. ⟨hal-02477135⟩