Abstract
Accurate decay data of radionuclides are necessary for many fields of science and technology, ranging from medicine and particle physics to metrology. However, data that are in use today are mostly based on measurements or theoretical calculation methods that are rather old. Recent measurements with cryogenic detectors and other methods show significant discrepancies to both older experimental data and theory in some cases. Moreover, the old results often suffer from large or underestimated uncertainties. This is in particular the case for electron-capture (EC) decays, where only a few selected radionuclides have ever been measured. To systematically address these shortcomings, the European metrology project MetroMMC aims at investigating six radionuclides decaying by EC. The nuclides are chosen to cover a wide range of atomic numbers Z, which results in a wide range of decay energies and includes different decay modes, such as pure EC or EC accompanied by gamma - and/or beta ^{+}-transitions. These will be measured using metallic magnetic calorimeters (MMCs), cryogenic energy-dispersive detectors with high-energy resolution, low-energy threshold and high, adjustable stopping power that are well suited for measurements of the total decay energy and X-ray spectrometry. Within the MetroMMC project, these detectors are used to obtain X-ray emission intensities of external sources as well as fractional EC probabilities of sources embedded in a 4pi absorber. Experimentally determined nuclear and atomic data will be compared to state-of-the-art theoretical calculations which will be further developed within the project. This contribution introduces the MetroMMC project and in particular its experimental approach. The challenges in EC spectrometry are to adapt the detectors and the source preparation to the different decay channels and the wide energy range involved, while keeping the good resolution and especially the low-energy threshold to measure the EC from outer shells.
Highlights
Radionuclides that decay by electron capture (EC) play an important role in many fields such as nuclear medicine, nuclear waste disposal, geo- and cosmo-chronology and even for testing the standard model of particle physics in various ways, e.g., in neutrino physics [3,4,5,6]
Several EC nuclides are being used in medicine or considered as candidates for medical applications, e.g., 67Ga and 125I
The determination of photon emission intensities is based on accurate activity standardization
Summary
Radionuclides that decay by electron capture (EC) play an important role in many fields such as nuclear medicine, nuclear waste disposal, geo- and cosmo-chronology (see, e.g., [1,2] and references therein) and even for testing the standard model of particle physics in various ways, e.g., in neutrino physics [3,4,5,6]. The nuclides were chosen both for scientific reasons and practical ones, e.g., that the material is available in the required amounts, has sufficiently low radioactive contaminants, has a sufficiently long half-life and is compatible with sample preparation techniques, that are established or require a reasonable amount of development Both 41Ca and 59Ni are used for dating of the solar system, meteorites and in geology and 41Ca plays a role in safety of nuclear waste disposal. The other isotopes have more difficult decay schemes, which make both experimental design and theoretical description more challenging This is supported by the fact that the chosen nuclides cover a wide range of atomic number Z and different decay natures, e.g., allowed, 2nd forbidden etc. In addition 125I is of interest because of its use in nuclear medicine
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