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The precision of existing decay data of radionuclides for activity determination is often a limitation for actual applications in science, society and industry. For this reason, the EMPIR project PrimA-LTD aims to introduce an advanced primary activity standardization technique that is based on magnetic microcalorimeters (MMCs) and that will offer very low energy threshold of few eV and a decay scheme-independent detection efficiency close to 100 % . As a proof of concept, we developed two MMC-based detector types in order to standardize an α -decaying, a β -decaying and an electron capture decaying isotope. One detector type aims to introduce a reusable detector setup, while the other aims to provide highly accurate decay spectra by high-resolution measurements with high statistics. We present the designs, fabrication status and first characterization measurements of both detectors types and outline next steps. [ABSTRACT FROM AUTHOR]

Low temperature detectors (LTDs) are high energy resolution energy dispersive spectrometers. Therefore, they are suitable for accurate measurements of X-ray or gamma-ray transition energies. However, the energy response of LTDs is non-linear. Therefore, it is required to correct the non-linearity to provide precise and accurate measurement. In this work, we present the study of the non-linearity of an LTD based on metallic magnetic sensors having an energy resolution below around 50 eV up to energies of 200 keV. The non-linearity was measured using a mix of radionuclides, 241Am, 152Eu, 210Pb, 129I and 139Ce, emitting X-rays and gamma-rays below 200 keV. The pulse energies and the energy spectra were obtained from different types of signal processing to evaluate their impact on the non-linearity. In addition, pulses were recorded with different preamplifier gains to identify possible non-linearity arising from the electronics and the DAQ. Finally the measured non-linearities were compared with the calculated non-linearity form the thermodynamic quantities of the MMC. • Energy non-linearity measurement of a low temperature detector using radionuclides. • Study of the non-linearity of an MMC under different recording conditions. • Influence on the non-linearity of different signal processing methods. • Comparison between experimental and calculated non-linearities. [ABSTRACT FROM AUTHOR]

Knowledge of absolute emission intensities of X-ray lines below 100 keV is limited or missing. An absolute determination of these intensities necessitates a high-resolution spectrometer with an accurate efficiency calibration. In this work, we will show and discuss the FEP efficiency calibration of a MMC detector combining a measurement of a standard source with Monte Carlo simulations using the code PENELOPE-2014. The simulated efficiency detection successfully interpolated the experimental efficiency values. [ABSTRACT FROM AUTHOR]

Energy dispersive photon spectrometry is a common analysis technique to quantify radionuclides present in a sample, the analysis is based on the knowledge of the photon emission intensities specific to each radionuclide. Among them, actinides have in general intense emission of L X-rays during the decay. However, their emission intensities are not well known and not detailed in the nuclear and atomic data tables due to the complexity of their spectra that cannot be resolved by conventional semiconductor spectrometers. Using a dedicated high energy resolution cryogenic detector, based on metallic magnetic calorimeter sensor technology, the L X-ray spectra of the decays of 238Pu(α) → 234U, 244Cm(α) → 240Pu, 237Np(α) → 233Pa and 233Pa(β − ) → 233U were measured with an energy resolution between 23 eV and 43 eV (full width at half maximum) given access to an unprecedented level of detail. Moreover, the detector was conceived to provide a quasi-constant efficiency in the energy range of the L X-rays, minimizing the uncertainty for relative L X-ray emission intensities. Prior to the measurements, the full energy peak efficiency was carefully characterized, which enabled the determination of absolute emission intensities, with an uncertainty of the order of 1%. Some corrections had to be introduced using Monte Carlo simulations, in particular to take into account the surface activity inhomogeneities of the sources. Total and group L X-ray emission intensities are compared with the available data and with the recommended values. In addition, nearly 30 individual L X-ray intensities are presented. [Display omitted] • Measurement of tens of L X-ray emission intensities emitted by actinides • A cryogenic spectrometer with an energy resolution of 23 to 43 eV • An intrinsic efficiency close to 100% between 10 keV and 25 keV • Detailed uncertainty contributions from the efficiency and the sources • Comparison of the measured intensities with available data [ABSTRACT FROM AUTHOR]

Emissions of L-X-rays by actinides are quite intense due to the large internal conversion coefficients of the gamma transitions. These emissions can be beneficial for the quantitative analysis of actinides by photon spectrometry, however the L X-rays emitted by radionuclides are generally not well known. Several studies explored the L-X-ray regions of actinides and measured total intensities of L-X-ray groups with large uncertainties up to 10%. However, they cannot resolve the individual L-X-ray lines due to the limited energy resolution (of the order of 200 eV (FWHM) at 25 keV) of the semiconductor detectors. The present work shows and discusses the measurement of individual L-X-ray emission intensities emitted by Cm-244 using an ultra-high-resolution spectrometer. The used spectrometer is a Metallic Magnetic Calorimeter (MMC) conceived for photon spectrometry below 100 keV with an energy resolution of 37 eV at 20 keV and a nearly constant efficiency over the L X-ray energy range. A high-resolution spectrum with a counting statistics of 4.6 × 106 counts was obtained. The spectrum processing allowed to determine the individual emission intensities of 30 L-X-ray lines despite the narrow energy spacing. [ABSTRACT FROM AUTHOR]

The beta decay of 151Sm was measured by means of a metallic magnetic calorimeter. The measurement and subsequent analysis yielded a beta spectrum with an outstanding high-energy resolution of about 70 eV (FWHM) at 22 keV and a very low energy threshold well below 400 eV. The spectrum exhibited unexpectedly elevated beta emission probabilities at very low energy that we have not been able to reproduce in our theoretical study. The data analysis was thus scrutinized and an independent analysis of the same data set carried out. All new approaches have confirmed the previously found shape of the beta spectrum. The measured spectrum was compared to predictions from an advanced theoretical modeling that includes the atomic exchange effect, precise radiative corrections as well as the realistic nuclear structure that usually plays an important role in first forbidden non-unique transitions. The measured spectrum was then carefully analyzed to determine the maximum beta energy, which was found to be Q = 76.430(68) keV. The dominant beta decay of 151Sm populates the ground state of 151Eu, and a weak beta branch populates the first excited state of 151Eu. From our measurements, the probabilities of these two branches were determined to be 99.31(11)% and 0.69(11)%, respectively. • The beta decay of 151Sm was measured by means of a metallic magnetic calorimeter (MMC). • The determined spectrum has a very high energy resolution and low threshold. • The maximum beta energy was found to be 76.430(68) keV and has an unprecedented accuracy. • The decay probabilities of two beta branches were determined. • The spectrum exhibits unexpectedly elevated beta emission probabilities at very low energy. [ABSTRACT FROM AUTHOR]