Search

Using dilute silver erbium alloys as a paramagnetic temperature sensor in metallic magnetic calorimeters (MMCs) has the advantage of the host material not having a nuclear quadrupole moment, in contrast to the alternative of using gold erbium alloys. We present numerical calculations of the specific heat and magnetization of Ag:Er, which are necessary for designing and optimizing MMCs using this type of alloy as sensor material. The parameter ranges we consider are temperatures between $$1\,{\text {{mK}}}$$ 1 mK and $$1\,{\text {{K}}}$$ 1 K , external magnetic fields of up to $$20\,{\text {{mT}}}$$ 20 mT , and erbium concentrations of up to $$2000\,{\text {{ppm}}}$$ 2000 ppm . The system is dominated by an interplay of crystal field effects, Zeeman splitting, and the RKKY interaction between erbium ions, with certain specific constellations of erbium ions having noticeable effects on the specific heat. Increasing the external magnetic field or assuming a decreased strength of the RKKY interaction leads to a higher magnetization and a narrowing of the main Schottky peak, while changes in the erbium concentration can be well described by parameter scaling.

To reach ultra-low detection thresholds necessary to probe unprecedentedly low Dark Matter masses, target material alternatives and novel detector designs are essential. One such target material is superfluid $^4$He which has the potential to probe so far uncharted light Dark Matter parameter space at sub-GeV masses. The new ``Direct search Experiment for Light dark matter'', DELight, will be using superfluid helium as active target, instrumented with magnetic micro-calorimeters. It is being designed to reach sensitivity to masses well below 100\,MeV in Dark Matter-nucleus scattering interactions., Comment: IDM2022 proceedings submitted to SciPost

In recent years, current-sensing dc-SQUIDs have enabled the application of noise thermometry at ultralow temperatures. A major advantage of noise thermometry is the fact that no driving current is needed to operate the device and thus the heat dissipation within the thermometer can be reduced to a minimum. Such devices can be used either in primary or relative primary mode and cover typically several orders of magnitude in temperature extending into the low microkelvin regime. Here we will review recent advances of noise thermometry for ultralow temperatures.

Due to their excellent energy resolution, the intrinsically fast signal rise time, the huge energy dynamic range, and the almost ideally linear detector response, metallic magnetic calorimeters (MMC)s are very well suited for a variety of applications in physics. In particular, the ECHo experiment aims to utilize large-scale MMC-based detector arrays to investigate the mass of the electron neutrino. Reading out such arrays is a challenging task which can be tackled using microwave SQUID multiplexing. Here, the detector signals are transduced into frequency shifts of superconducting microwave resonators, which can be deduced using a high-end software-defined radio (SDR) system. The ECHo SDR system is a custom-made modular electronics, which provides 400 channels equally distributed in a 4 to 8 GHz frequency band. The system consists of a superheterodyne RF frequency converter with two successive mixers, a modular conversion, and an FPGA board. For channelization, a novel heterogeneous approach, utilizing the integrated digital down conversion (DDC) of the ADC, a polyphase channelizer, and another DDC for demodulation, is proposed. This approach has excellent channelization properties while being resource-efficient at the same time. After signal demodulation, on-FPGA flux-ramp demodulation processes the signals before streaming it to the data processing and storage backend.

MetroBeta, a recently completed European Metrology Research Project, aimed at the improvement of the knowledge of the shapes of beta spectra, both in terms of theoretical calculation and measurement. The most prominent experimental work package concerned the measurement of the spectrum shapes of several beta decaying radionuclides by means of metallic magnetic calorimeters (MMCs) with the beta emitter embedded in the absorber. New MMC chips were designed and optimized for five different absorber heat capacities, enabling the measurement of beta spectra with Q values ranging from few tens of keV up to ~ 1 MeV. Several beta spectra were measured with high energy resolution and statistics of up to 107 counts.

We present a hybrid microwave SQUID multiplexer that combines two frequency-division multiplexing techniques to allow multiplexing a given number of cryogenic detectors with only a fraction of frequency encoding resonators. Similar to conventional microwave SQUID multiplexing, our multiplexer relies on inductively coupling non-hysteretic, unshunted rf-SQUIDs to superconducting microwave resonators as well as applying flux ramp modulation for output signal linearization. However, instead of utilizing one resonator per SQUID, we couple multiple SQUIDs to a common readout resonator and encode the SQUID input signals in sidebands of the microwave carrier by varying the flux ramp modulation frequency for each SQUID. We prove the suitability of our approach using a prototype device and argue by means of fundamental information theory that our approach is particularly suited for reading out large cryogenic bolometer arrays., Comment: The following article has been submitted to Applied Physics Letters

The European Physical Society Conference on High Energy Physics, Online conference, jointly organized by Universität Hamburg and the research center DESY; he European Physical Society Conference on High Energy Physics (EPS-HEP2021) 398, 4 pp. (2022). doi:10.22323/1.398.0211, Published by Sissa Medialab Trieste, Italy

Metallic magnetic micro-calorimeters (MMCs) operated at millikelvin temperature offer the possibility to achieve eV-scale energy resolution with high stopping power for X-rays and massive particles in an energy range up to several tens of keV. This motivates their use in a wide range of applications in fields as particle physics, atomic and molecular physics. Present detector systems consist of MMC arrays read out by 32 two-stage SQUID read-out channels. In contrast to the design of the detector array and consequently the design of the front-end SQUIDs, which need to be optimised for the physics case and the particles to be detected in a given experiment, the read-out chain can be standardised. We present our new standardised 32-channel parallel read-out for the operation of MMC arrays to be operated in a dilution refrigerator. The read-out system consists of a detector module, whose design depends on the particular application, an amplifier module, ribbon cables from room temperature to the millikelvin platform and a data acquisition system. In particular, we describe the realisation of the read-out system prepared for the ECHo-1k experiment for the operation of two 64-pixel arrays. The same read-out concept is also used for the maXs detector systems, developed for the study of the de-excitation of highly charged heavy ions by X-rays, as well as for the MOCCA system, developed for the energy and position sensitive detection of neutral molecular fragments for the study of fragmentation when molecular ions recombine with electrons. The choice of standard modular components for the operation of 32-channel MMC arrays offer the flexibility to upgrade detector modules without the need of any changes in the read-out system and the possibility to individually exchange parts in case of damages or failures.

Axion helioscopes like the planned International Axion Observatory (IAXO) search for evidence of axions and axion-like particles (ALPs) from the Sun. A strong magnetic field is used to convert ALPs into photons via the generic ALP-photon coupling. To observe the resulting photons, X-ray detectors with low background and high efficiency are necessary. In addition, good energy resolution and low energy threshold would allow for investigating the ALP properties by studying the X-ray spectrum after its discovery. We propose to use low temperature metallic magnetic calorimeters (MMCs). Here we present the first detector system based on MMCs developed for IAXO and discuss the results of the characterization. The detector consists of a two-dimensional 64-pixel array covering an active area of 16mm2 with a fill factor of 93%. We achieve an average energy resolution of 6.1 eV FWHM allowing for energy thresholds below 100 eV. This detector is the first step towards a larger 1 cm2 array matching the IAXO X-ray optics. We determine the background rate for an unshielded detector system in the energy range between 1 keV and 10 keV to be 3.2(1) × 10-4 keV-1 cm-2 s-1 from events acquired over 30 days. In the future, active and passive shields will significantly reduce the background induced by cosmic muons and natural radioactivity. Our results demonstrate that MMCs are a promising technology for helioscopes to discover and study ALPs.

We present a measurement of the low-energy (0-60 keV) γ-ray spectrum produced in the α decay of ^{233}U using a dedicated cryogenic magnetic microcalorimeter. The energy resolution of ∼10 eV, together with exceptional gain linearity, allows us to determine the energy of the low-lying isomeric state in ^{229}Th using four complementary evaluation schemes. The most precise scheme determines the ^{229}Th isomer energy to be 8.10(17) eV, corresponding to 153.1(32) nm, superseding in precision previous values based on γ spectroscopy, and agreeing with a recent measurement based on internal conversion electrons. We also measure branching ratios of the relevant excited states to be b_{29}=9.3(6)% and b_{42}

The goal for the ECHo experiment is the determination of the effective electron neutrino mass by analyzing the electron capture (EC) spectrum of $^{163}$Ho. Metallic magnetic calorimeters enclosing $^{163}$Ho, achieved very good performance to conduct such an experiment. During the first phase of the experiment, ECHo-1k, the detector production and the implantation process of high purity $^{163}$Ho have been optimized. Large detector arrays have been developed, featuring energy resolution below 5eV and activity of about 1Bq per pixel. High statistics and high resolution $^{163}$Ho spectra have been acquired and analyzed in light of new theoretical description of the spectral shape, considering the independently determined Q$_{\mathrm{EC}}$-value, and a dedicated background model. In this contribution, we present preliminary results obtained in the first phase of ECHo. At the same time, we discuss the necessary upgrades towards the second phase of the experiment, ECHo-100k.

We have developed a new micro-fabricated platform for the measurement of the specific heat of low heat capacity mg-sized metallic samples, such as superconductors, down to temperatures of as low as $10\,\mathrm{mK}$. It addresses challenging aspects of setups of this kind such as the thermal contact between sample and platform, the thermometer resolution, and an addenda heat capacity exceeding that of the samples of interest (typically $\mbox{nJ/K at }20\,\mbox{mK}$). The setup allows us to use the relaxation method, where the thermal relaxation following a well defined heat pulse is monitored to extract the specific heat. The sample platform ($5 \times 5\, \mathrm{mm^2}$) includes a micro-structured paramagnetic \underline{Ag}:Er temperature sensor, which is read out by a dc-SQUID via a superconducting flux transformer. In this way, a relative temperature precision of $30\,\mathrm{nK/\sqrt{Hz}}$ can be reached, while the addenda heat capacity falls well below $0.5\,\mathrm{nJ/K}$ for $T < 300\,\mathrm{mK}$. A gold-coated mounting area ($4.4 \times 3 \, \mathrm{mm^2}$) is included to improve the thermal contact between sample and platform., 8 pages, 7 figures; the following article has been accepted by Review of Scientific Instruments. After it is published, it will be found at https://publishing.aip.org/resources/librarians/products/journals/

The specific heat of dilute alloys of holmium in gold and in silver plays a major role in the optimization of low temperature microcalorimeters with enclosed $^{163}\textrm{Ho}$, such as the ones developed for the neutrino mass experiment ECHo. We investigate alloys with atomic concentrations of $x_\textrm{Ho}=0.01\,\% - 4\,\%$ at temperatures between $10\,\textrm{mK}$ and $800\,\textrm{mK}$. Due to the large total angular momentum $J=8$ and nuclear spin $I=7/2$ of $\textrm{Ho}^{3+}$ ions, the specific heat of $\underline{\textrm{Au}}\textrm{:Ho}$ and $\underline{\textrm{Ag}}\textrm{:Ho}$ depends on the detailed interplay of various interactions, including contributions from the localized 4f electrons and nuclear contributions via hyperfine splitting. This makes it difficult to accurately determine the specific heat of these materials numerically. Instead, we measure their specific heat by using three experimental set-ups optimized for different concentration and temperature ranges. The results from measurements on six holmium alloys demonstrate that the specific heat of these materials is dominated by a large Schottky anomaly with its maximum at $T\approx 250\,\textrm{mK}$, which we attribute to hyperfine splitting and crystal field interactions. RKKY and dipole-dipole interactions between the holmium atoms cause additional, concentration-dependent effects. With regard to ECHo, we conclude that for typical operating temperatures of $T\leq 20\,\textrm{mK}$, silver holmium alloys with $x_\textrm{Ho}\gtrsim 1\,\%$ are suited best., 15 pages, 4 figures. Replacement with small modifications after peer-review, no change to scientific content

We have used different metallic magnetic calorimeter (MMC) gamma detectors to measure the low-energy emissions of 233U with an accuracy of a few eV. 233U is of interest in nuclear safeguards because it is a fissile isotope that is produced by neutron irradiation of 232Th in the thorium fuel cycle. However, some of the nuclear decay data of 233U in the literature have relatively high uncertainties, especially at lower energies where lines can overlap or be dominated by a high Compton background. MMC gamma detectors operated at a temperature of 10 mK can have an energy resolution below 50 eV and can resolve lines with similar energy and reduce these uncertainties. We present recent MMC measurements of 233U and discuss the contributions of statistical and systematic errors. Importantly, we have performed the experiments with different MMC gamma detectors and different SQUID readout systems to increase the confidence in some observed deviations from literature values. The consistency of the results suggest that observed deviations are not due to detector artifacts and that a predictable quadratic response is intrinsic to the properties of MMCs.

The European physical journal / C Particles and fields C 79(12), 1026 (2019). doi:10.1140/epjc/s10052-019-7513-x, Published by Springer, Heidelberg

Precise nuclear data from radioactive decays are important for the accurate non-destructive assay of fissile materials in nuclear safeguards. We are developing high energy resolution gamma detectors based on metallic magnetic calorimeters (MMCs) to accurately measure gamma-ray energies and branching ratios of uranium isotopes. Our MMC gamma detectors exhibit good linearity, reproducibility and a consistent response function for low energy gamma-rays. We illustrate the capabilities of MMCs to improve literature values of nuclear data with an analysis of gamma spectra of U-233. In this context, we also improve the value of the energy for the single gamma-ray of the U-233 daughter Ra-225 by over an order of magnitude from 40.09 ± 0.05 to 40.0932 ± 0.0007 keV.

Metallic magnetic calorimeters (MMCs) are calorimetric low-temperature particle detectors that are currently strongly advancing the state of the art in energy-dispersive single particle detection. They are typically operated at temperatures below $$100\,\mathrm {mK}$$ and make use of a metallic, paramagnetic temperature sensor to transduce the temperature rise of the detector upon the absorption of an energetic particle into a change of magnetic flux which is sensed by a superconducting quantum interference device. This outstanding interplay between a high-sensitivity thermometer and a near quantum-limited amplifier results in a very fast signal rise time, an excellent energy resolution, a large dynamic range, a quantum efficiency close to 100% as well as an almost ideal linear detector response. For this reason, a growing number of groups located all over the world is developing MMC arrays of various sizes which are routinely used in a variety of applications. Within this paper, we briefly review the state of the art of metallic magnetic calorimeters. This includes a discussion of the detection principle, sensor materials and detector geometries, readout concepts, the structure of modern detectors as well as the state-of-the-art detector performance.

Several experiments on the study of the electron neutrino mass are based on high-statistics measurements of the energy spectrum following electron capture of the radionuclide 163Ho. They rely on the availability of large, radiochemically pure samples of 163Ho. Here, we describe the production, separation, characterization, and sample production within the Electron Capture in Holmium-163 (ECHo) project. 163Ho has been produced by thermal neutron activation of enriched, prepurified 162Er targets in the high flux reactor of the Institut Laue-Langevin, Grenoble, France, in irradiations lasting up to 54 days. Irradiated targets were chemically processed by means of extraction chromatography, which allowed separating the formed Ho from the 162Er target-material and from the main byproducts 170Tm and 171Tm, which are co-produced in GBq amounts. Decontamination factors of >500 for Er and of >105 for Tm and yields of 3.6·1016 and 1.2·1018 atoms of 163Ho were obtained, corresponding to a recovery yield of 95 % of Ho in the chemical separation. The Ho-fraction was characterized by means of γ-ray spectrometry, Inductively-Coupled-Plasma Mass Spectrometry (ICP-MS), Resonance Ionization Mass Spectrometry (RIMS) and Neutron Activation Analysis (NAA). In this process, the thermal neutron capture cross section of 163Ho was measured to σHo-163 to Ho-164m= (23±3) b and σHo-163 to Ho-164g= (156±9) b for the formation of the two isomers of 164Ho. Specific samples were produced for further purification by mass separation to isolate 163Ho from the Ho-isotope mixture, as needed for obtaining the energy spectrum within ECHo. The partial efficiency for this second separation step is (32±5) %.

To our present best knowledge, microwave SQUID multiplexing ( $$\mu $$ MUXing) is the most suitable technique for reading out large-scale low-temperature microcalorimeter arrays that consist of hundreds or thousands of individual pixels which require a large readout bandwidth per pixel. For this reason, the present readout strategy for metallic magnetic calorimeter (MMC) arrays combining an intrinsic fast signal rise time, an excellent energy resolution, a large energy dynamic range, a quantum efficiency close to $$100\%$$ as well as a highly linear detector response is based on $$\mu $$ MUXing. Within this paper, we summarize the state of the art in MMC $$\mu $$ MUXing and discuss the most recent results. This particularly includes the discussion of the performance of a 64-pixel detector array with integrated, on-chip microwave SQUID multiplexer, the progress in flux ramp modulation of MMCs as well as the status of the development of a software-defined radio-based room-temperature electronics which is specifically optimized for MMC readout.

This paper reports on the development of a technology involving $$^{100}\hbox {Mo}$$ 100 Mo -enriched scintillating bolometers, compatible with the goals of CUPID, a proposed next-generation bolometric experiment to search for neutrinoless double-beta decay. Large mass ( $$\sim 1~\hbox {kg}$$ ∼ 1 kg ), high optical quality, radiopure $$^{100}\hbox {Mo}$$ 100 Mo -containing zinc and lithium molybdate crystals have been produced and used to develop high performance single detector modules based on 0.2–0.4 kg scintillating bolometers. In particular, the energy resolution of the lithium molybdate detectors near the Q-value of the double-beta transition of $$^{100}\hbox {Mo}$$ 100 Mo (3034 keV) is 4–6 keV FWHM. The rejection of the $$\alpha $$ α -induced dominant background above 2.6 MeV is better than $$8\sigma $$ 8 σ . Less than $$10~\upmu \hbox {Bq/kg}$$ 10 μ Bq/kg activity of $$^{232}\hbox {Th}\, (^{228}\hbox {Th})$$ 232 Th ( 228 Th ) and $$^{226}\hbox {Ra}$$ 226 Ra in the crystals is ensured by boule recrystallization. The potential of $$^{100}\hbox {Mo}$$ 100 Mo -enriched scintillating bolometers to perform high sensitivity double-beta decay searches has been demonstrated with only $$10~\hbox {kg}\times \hbox {d}$$ 10 kg × d exposure: the two neutrino double-beta decay half-life of $$^{100}\hbox {Mo}$$ 100 Mo has been measured with the up-to-date highest accuracy as $$T_{1/2}$$ T 1 / 2 = [6.90 ± 0.15(stat.) ± 0.37(syst.)] $$\times ~10^{18}~\hbox {years}$$ × 10 18 years . Both crystallization and detector technologies favor lithium molybdate, which has been selected for the ongoing construction of the CUPID-0/Mo demonstrator, containing several kg of $$^{100}\hbox {Mo}$$ 100 Mo .

Several novel experiments designed to investigate the electron neutrino mass in the sub-eV region are based on the calorimetric measurement of the 163Ho electron capture spectrum. For this the 163Ho source, with a required activity of the order of 1 to 100 Bq , needs to be enclosed in the detector, having a volume smaller than 10 − 3 mm 3 . Ion implantation is presently considered to be the most reliable method to enclose this source in the detector homogeneously distributed in a well defined volume. We have investigated the distribution of implanted holmium ions in different target materials and for different implantation energies by means of Monte Carlo simulations based on the SRIM software package. We show that, for a given implantation energy, a given target material and implantation area, the number of holmium ions that can be implanted in a single implantation run is limited. We discuss possible methods to overcome this saturation limit in order to fabricate detectors with an enclosed 163Ho source of the activity required by the experiments.

Metallic magnetic calorimeters are energy-dispersive cryogenic particle detectors providing an excellent energy resolution, a fast signal rise time, a high quantum efficiency as well as an almost ideal linear detector response. To surpass the present record resolution of 1.6 eV (FWHM) for 6 keV photons, we have started to develop integrated detectors for which the paramagnetic temperature sensor monitoring the temperature rise of the detector is integrated directly into the pickup loop of the superconducting quantum interference device. Due to the greatly enhanced magnetic flux coupling and consequently the reduced contribution of SQUID noise to the overall noise spectrum, this kind of devices should push the resolution to a value well below 1 eV. Here, we discuss the design and performance of a prototype 64 pixels metallic magnetic calorimeter based detector array with integrated detectors that rely on first-order parallel gradiometric SQUIDs with two meander-shaped pickup coils onto which planar temperature sensor made of Ag:Er are deposited.

We present a novel dc-SQUID readout scheme that provides linearization of the relation between the input and output signal without using a conventional flux-locked loop circuit. It relies on applying a periodic, sawtooth-shaped magnetic flux signal to the modulation coil of the SQUID to continuously measure the flux-to-voltage SQUID characteristic within each period of the flux ramp. In case that the amplitude and repetition rate of the ramp are chosen such that multiple flux quanta are induced in the SQUID and that the input signal is quasistatic within one period of the flux ramp, the input signal adds a constant magnetic flux offset to the SQUID that leads to a phase shift of the SQUID characteristic being proportional to the input signal. We show that this scheme allows for significantly increasing the dynamic range and that it intrinsically allows for MHz frequency-division SQUID multiplexing.

The aim of the European Metrology Research Project MetroBeta is to improve the knowledge of the shapes of beta spectra, both in terms of theoretical calculation and measurement. The precise knowledge of beta spectra is required for the activity standardisation of pure beta emitters. Metallic magnetic calorimeters (MMCs), a type of cryogenic detectors, with the beta emitter embedded in the absorber have proven to be among the best beta spectrometers, in particular for low-energy beta transitions. Within this project, new designs of MMCs optimized for five different beta energy ranges were developed and a new detector module was constructed. The beta spectra of 151Sm, 14C and 99Tc have been measured so far; additional measurements with 36Cl are under preparation. Improved theoretical calculation methods and complementary measurement techniques complete the project.

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 $$\gamma $$γ- and/or $$\beta ^{+}$$β+-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 $$4\pi $$4π 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.

International audience; MetroBeta is a European project aiming at the improvement of the knowledge of the shapes of beta spectra, both in terms of theoretical calculations and measurements. It is part of a common European program of ionizing radiation metrology. Metallic magnetic calorimeters (MMCs) with the beta emitter embedded in the absorber have in the past proven to be among the best beta spectrometers, in particular for low-energy beta transitions. Within this project, new designs of MMCs optimized for five different beta energy ranges were developed. A new detector module with thermal decoupling of MMC and SQUID chips was designed. An important aspect of the research and development concerns the source/absorber preparation techniques. Four beta spectra with maximum energies ranging from 76 to 709 keV will be measured. Improved theoretical calculation methods and complementary measurement techniques complete the project.

We present a MHz frequency-division dc-SQUID multiplexer that is based on flux ramp modulation and a series array of $N$ identical current-sensing dc-SQUIDs with tightly coupled input coil. By running a periodic, sawtooth-shaped current signal through an additional modulation coil being tightly, but non-uniformly coupled to the individual SQUIDs, the voltage drop across the array changes according to the superposition of the flux-to-voltage characteristics of the individual SQUIDs within each cycle of the modulation signal. In this mode of operation, an input signal injected in the input coil of one of the SQUIDs and being quasi-static within a time frame adds a constant flux offset and leads to a phase shift of the associated SQUID characteristics. The latter is inherently proportional to the input signal and can be inferred by channelizing and down-converting the sampled array output voltage. Using a prototype multiplexer as well as a self-developed high-speed readout electronics for real-time phase determination, we demonstrate the simultaneous readout of four signal sources with MHz bandwidth per channel., The article has been submitted to Applied Physics Letters

We present the design of MOCCA, a large-area particle detector that is developed for the position- and energy-resolving detection of neutral molecule fragments produced in electron–ion interactions at the Cryogenic Storage Ring at the Max Planck Institute for Nuclear Physics in Heidelberg. The detector is based on metallic magnetic calorimeters and consists of 4096 particle absorbers covering a total detection area of $$44.8\,\mathrm {mm} \times 44.8\,\mathrm {mm}$$ . Groups of four absorbers are thermally coupled to a common paramagnetic temperature sensor where the strength of the thermal link is different for each absorber. This allows attributing a detector event within this group to the corresponding absorber by discriminating the signal rise times. A novel readout scheme further allows reading out all 1024 temperature sensors that are arranged in a $$32 \times 32$$ square array using only $$16+16$$ current-sensing superconducting quantum interference devices. Numerical calculations taking into account a simplified detector model predict an energy resolution of $$\Delta E_\mathrm {FWHM} \le 80\,\mathrm {eV}$$ for all pixels of this detector.

Metallic magnetic calorimeters (MMCs) are highly linear cryogenic detectors that offer an excellent energy resolution, a signal rise time of

The determination of the electron neutrino mass by electron capture in $^{163}\mathrm{Ho}$ relies on a precise understanding of the deexcitation of a core hole after an electron-capture event. Here we present an ab initio calculation of the electron-capture spectrum of $^{163}\mathrm{Ho}$, i.e., the $^{163}\mathrm{Ho}$ decay rate as a function of the energy distribution between the $^{163}\mathrm{Dy}$ daughter atom and the neutrino. Our current level of theory includes all intra-atomic decay channels and many-body interactions on a basis of fully relativistic bound orbitals. We use theoretical methods developed and extensively used for the calculation of core level spectroscopy on correlated electron materials. Our comparison to experimental electron-capture data critically tests the accuracy of these theories. We find that relativistic interactions beyond the Dirac equation lead to only minor shifts of the spectral peaks. The electronic relaxation after an electron-capture event due to the modified nuclear potential leads to a mixing of different edges, but, due to conservation of angular momentum of each scattered electron, no additional structures emerge. Many-body Coulomb interactions lead to the formation of multiplets and to additional peaks corresponding to multiple core holes created via Auger decay. Multiplets crucially change the appearance of the resonances on a Rydberg energy scale. The additional structures due to Auger decay are, although clearly visible, relatively weak compared to the single core hole states and are incidentally far away from the end-point region of the spectrum. As the end point of the spectrum is affected most by the neutrino mass, these additional states do not directly influence the statistics for determining the neutrino mass. The multiplet broadening and Auger shake-up of the main core-level edges do, however, change the apparent linewidth and accompanying lifetime of these edges. Fitting core-level edges, either in electron-capture spectroscopy or in x-ray absorption spectroscopy, by a single resonance thus leads to an underestimation of the core hole lifetime.

The growing demands of quantum materials, engineering and technology make access to microkelvin temperatures ever more essential. Experience in Europe suggests that new working methods, encouraged by an imaginative funding atmosphere, can accelerate progress in this frontier field.

Metallic magnetic calorimeters (MMCs) are cryogenic detectors that offer an excellent energy resolution, a signal rise time of below 100 ns, a high dynamic range and almost optimal linearity. MMCs are of high interest for many experiments, such as dark matter detection or direct neutrino mass investigations. Since larger detector arrays are read out at GHz-Frequencies, and each single pixel offers a fast rise time, a complex analog and digital readout system is required. This contribution will give an introduction to MMC technology in combination with the implemented readout electronics and the current status of the present readout architecture.

Atoms 6(4), 59 - (2018). doi:10.3390/atoms6040059 special issue: "Perspectives of Atomic Physics with Trapped Highly Charged Ions)", Published by MDPI, Basel

Cryogenic high-resolution $$\gamma $$ -ray detectors can improve the accuracy of non-destructive assay (NDA) of nuclear materials in cases where conventional high-purity germanium detectors are limited by line overlap or by the Compton background. We have improved the performance of gamma detectors based on metallic magnetic calorimeters (MMCs) by separating the 0.5 $$\times $$ 2 $$\times $$ 0.25 mm $$^{3}$$ Au absorber from the Au:Er sensor with sixteen 30- $$\upmu $$ m-diameter Au posts. This ensures that the entire $$\gamma $$ -ray energy thermalizes in the absorber before heating the Au:Er sensor, and improves the energy resolution at 35 mK to as low as 90 eV FWHM at 60 keV. This energy resolution enables the direct detection of $$\gamma $$ -rays from Pu-242, an isotope that cannot be measured by traditional NDA and whose concentration is therefore inferred through correlations with other Pu isotopes. The Pu-242 concentration of 11.11 $$\pm $$ 0.42 % measured by NDA with MMCs agrees with mass spectrometry results and exceeds the accuracy of correlation measurements.

Metallic magnetic calorimeters (MMCs) are low-temperature particle detectors that are typically read out by using superconducting quantum interference devices (SQUIDs). But since MMCs are sensitive to the input circuitry and the noise performance of the SQUID, the energy resolution of MMCs have not yet reached their fundamental limit. A possible solution to overcome present limits is to maximize the flux coupling by minimizing parasitic inductance in the input circuit. To show the suitability of this approach, we realized a 64 pixel MMC detector array with integrated dc-SQUID readout, i.e., detector and SQUID are on the same chip. We observed an influence of the power dissipation of the SQUID on the detector temperature. We achieved a baseline energy resolution of $$\Delta E_\mathrm {FWHM} = 25\,\mathrm {eV}$$ and $$\Delta E_\mathrm {FWHM} = 30\,\mathrm {eV}$$ for X-rays with energies up to $$6\,\mathrm {keV}$$ .

The isotope ^{163}Ho is in many ways the best candidate to perform experiments to investigate the value of the electron neutrino mass. It undergoes an electron capture process to ^{163}Dy with an energy available to the decay, Q_{EC}, of about 2.8 keV. According to the present knowledge, this is the lowest Q_{EC} value for such transitions. Here we discuss a newly obtained spectrum of ^{163}Ho, taken by cryogenic metallic magnetic calorimeters with ^{163}Ho implanted in the absorbers and operated in anticoincident mode for background reduction. For the first time, the atomic deexcitation of the ^{163}Dy daughter atom following the capture of electrons from the 5s shell in ^{163}Ho, the OI line, was observed with a calorimetric measurement. The peak energy is determined to be 48 eV. In addition, a precise determination of the energy available for the decay Q_{EC}=(2.858±0.010_{stat}±0.05_{syst}) keV was obtained by analyzing the intensities of the lines in the spectrum. This value is in good agreement with the measurement of the mass difference between ^{163}Ho and ^{163}Dy obtained by Penning-trap mass spectrometry, demonstrating the reliability of the calorimetric technique.

We report on the first demonstration of a scalable GHz frequency-domain readout of metallic magnetic calorimeters (MMCs) using a 64 pixel detector array that is read out by an integrated, on-chip microwave SQUID multiplexer. The detector array is optimized for detecting soft X-ray photons and the multiplexer is designed to provide a signal rise time τrise