Impact on industrial and other user communities The project will help to reduce uncertainties of nuclear decay data and to obtain activity standards with improved accuracy which are required for industrial applications. In some cases (e.g. 41Ca), the reduced uncertainties of EC probabilities will lead to a considerable reduction of the uncertainty of the corresponding half-life which is relevant for radioactive waste management. Improved knowledge of the emission probabilities of Auger electrons and X-rays at each energy level is very important for EC nuclides used in nuclear medicine since the estimation of the administered dose greatly depends on these data. Impact on the metrology and scientific communities Experimentally determined EC probabilities and X-ray emission intensities will lead to improvements of theoretical calculation methods. The measured data and improved calculation methods will be an invaluable contribution to the realisation of the SI unit becquerel in radionuclide metrology. Radionuclide metrologists will be enabled to reduce uncertainties, which is important for several other fields where precise radioactivity measurements matter. This comprises geo- and cosmochronology, nuclear medicine as well as industrial applications, but also research in other fields. The improved calculation techniques of the electron capture process and its subsequent atomic relaxation are essential for a sound research of radiation effects in human tissue on the DNA level. The developments will also contribute to new basic research experiments which require measurements of ionizing radiation with high energy resolution. As an example, short baseline neutrino oscillation experiments at nuclear reactors would benefit from accurate EC probability measurements for the indispensable evaluation of background sources. Beyond the direct impact from the measurements on EC decaying nuclides, the advances in MMC and related readout techniques triggered by this project will be highly beneficial in numerous fields of applied and fundamental research in which MMCs play an increasingly important role. Some of the developments will also be applicable to other types of cryogenic detectors, thus reaching even more fields of research and further extending the outreach of the project. Impact on relevant standards The project will lead to improved nuclear decay data by direct measurements and by improving the theoretical calculation techniques. Hence, the outcome of this project will be a valuable contribution for nuclear decay data evaluations. The standard of the SI unit becquerel must be established for each radionuclide individually and generally consists in the standard method used for the activity standardisation of the respective nuclide. For several pure EC nuclides, the TDCR-LSC method is the standard method. A better knowledge of the electron and photon emission spectra will have immediate impact on the activity standards for EC decaying nuclides. Longer-term economic, social and environmental impacts This project will accelerate innovation and competitiveness in the field of the ground-breaking technology using MMCs and more generally cryogenic detectors. On a long-term perspective, MMC-based detectors may become a tool for enhanced nuclear spectrometry with an energy resolution which is much higher than with any semi-conductor detector. In particular, spectrometry at very low energy, where the detection efficiency of conventional techniques drastically drops off, benefits from the outstanding low energy threshold of MMCs, enabling substantial reduction of systematic effects. All in all, MMC detectors enable research and applications far beyond current limits which are, at present, defined by existing spectrometers based on semi-conductors. Due to the high potential of MMCs, it is anticipated that the technology will be more and more used in various disciplines. The nuclear decay data which will be determined with better precision within this project and beyond will be important in many fields such as nuclear medicine, industry or geo- and cosmochronology.