C. Pies

Metallic magnetic calorimeters

Metallic magnetic calorimeters (MMC) are calorimetric particle detectors, typically operated at temperatures below 100 mK, that make use of a paramagnetic temperature sensor to transform the temperature rise upon the absorption of a particle in the detector into a measurable magnetic flux change in a dc‐SQUID. During the last years a growing number of groups has started to develop MMC for a wide variety of applications, ranging from alpha‐, beta‐ and gamma‐spectrometry over the spatially resolved detection of accelerated molecule fragments to arrays of high resolution x‐ray detectors. For x‐rays with energies up to 6 keV an energy resolution of 2.7 eV (FWHM) has been demonstrated and we expect that this can be pushed below 1 eV with the next generation of devices. We give an introduction to the physics of MMCs and summarize the presently used readout schemes as well as the typically observed noise contributions and their impact on the energy resolution. We discuss general design considerations, the micro‐fabrication of MMCs and the performance of micro‐fabricated devices. In this field large progress has been achieved in the last years and the thermodynamic properties of most materials approach bulk values allowing for optimal and predictable performance.

Characterization of low temperature metallic magnetic calorimeters having gold absorbers with implanted 163Ho ions

For the first time we have investigated the behavior of fully micro-fabricated low temperature metallic magnetic calorimeters (MMCs) after undergoing an ion-implantation process. This experiment had the aim to show the possibility to perform a high precision calorimetric measurement of the energy spectrum following the electron capture of 163 Ho using MMCs having the radioactive 163 Ho ions implanted in the absorber. The implantation of 163 Ho ions was performed at ISOLDE-CERN. The performance of a detector that underwent an ion-implantation process is compared to the one of a detector without implanted ions. The results show that the implantation dose of ions used in this experiment does not compromise the properties of the detector. In addition an optimized detector design for future 163 Ho

Metallic Magnetic Calorimeters for X-Ray Spectroscopy

An increasing number of experiments employ low-temperature radiation/particle detectors which are based on a calorimetric detection scheme and operate at temperatures below 100 mK. Metallic magnetic calorimeters use a metallic paramagnetic temperature sensor in tight thermal contact with the X-ray absorber. The magnetization of the sensor is used to monitor the temperature change of the detector upon the absorption of single photons, which is proportional to the absorbed energy. Low-noise high-bandwidth dc superconducting quantum interference devices read out the small changes in magnetization. An energy resolution of DeltaE FWHM = 2.7 eV was obtained for X-ray energies up to 6 keV.

Cryogenic micro-calorimeters for mass spectrometric identification of neutral molecules and molecular fragments

We have systematically investigated the energy resolution of a magnetic micro-calorimeter (MMC) for atomic and molecular projectiles at impact energies ranging from E≈13 to 150 keV. For atoms we obtained absolute energy resolutions down to ΔE≈120 eV and relative energy resolutions down to ΔE/E≈10−3. We also studied in detail the MMC energy-response function to molecular projectiles of up to mass 56 u. We have demonstrated the capability of identifying neutral fragmentation products of these molecules by calorimetric mass spectrometry. We have modeled the MMC energy-response function for molecular projectiles and concluded that backscattering is the dominant source of the energy spread at the impact energies investigated. We have successfully demonstrated the use of a detector absorber coating to suppress such spreads. We briefly outline the use of MMC detectors in experiments on gas-phase collision reactions with neutral products. Our findings are of general interest for mass spectrometric techniques, par...

Reproducibility and calibration of MMC-based high-resolution gamma detectors

We describe a prototype γ-ray detector based on a metallic magnetic calorimeter with an energy resolution of 46 eV at 60 keV and a reproducible response function that follows a simple second-order polynomial. The simple detector calibration allows adding high-resolution spectra from different pixels and different cool-downs without loss in energy resolution to determine γ-ray centroids with high accuracy. As an example of an application in nuclear safeguards enabled by such a γ-ray detector, we discuss the non-destructive assay of 242Pu in a mixed-isotope Pu sample.

Metallic magnetic calorimeters for high precision QED tests at GSI/FAIR

The quantum electrodynamics belongs to the best tested and established theories in modern physics. However, the evaluation of high order processes, as necessary in the presence of large electric fields, is still demanding. Of particular interest in this field is the Lamb shift of highly charged, hydrogen‐like ions, as the theoretically claimed error bars start to be smaller than the experimental ones. We recently started to develop a 1×8 detector array for high resolution x‐ray spectroscopy of hydrogen‐like Uranium at the GSI/FAIR. The detectors are designed to have an energy resolution below 30 eV in the relevant energy range up to 100 keV. We discuss the considerations that lead to our present detector design, as well as the present micro‐fabrication techniques.

Physics and applications of metallic magnetic calorimeters for particle detection

An increasing number of experiments and applications employ low temperature particle detectors. Following the calorimetric detection principles, the energy released in the detector leads to a temperature increase which is measured by a very sensitive sensor. Metallic magnetic calorimeters are composed by an energy absorber, optimized for the particles to be detected, in good thermal contact with a metallic paramagnetic sensor positioned in a weak magnetic field. A change in the sensor magnetisation follows the change of the detector temperature. High energy resolution can be obtained by using a low-noise, high-bandwidth DC-SQUID to measure the corresponding change of flux. We discuss the thermodynamic properties, the energy resolution, the microfabrication and general design considerations of magnetic calorimeters as well as their application in high resolution x-ray spectroscopy, beta spectroscopy and absolute activity measurements.

Cryogenic micro-calorimeters for mass spectrometry of keV neutral atoms and molecules

We demonstrate the capability of micro-calorimeters to detect and mass-resolve neutral atoms and molecules at ~ keV energies, reaching single H-atom resolution.