Search

The fractional electron capture probabilities of 59Ni were measured using metallic magnetic calorimeters (MMCs). 59Ni was one of the radionuclides chosen as a part of the European Metrology Research (EMPIR) project MetroMMC. The measurement was performed by using the decay energy spectroscopy (DES) technique, where the radionuclide is embedded in the absorber to have a 4π geometry. Two different source preparation techniques adapted for the measurement are also discussed: electroplating on gold foil and micro-drop-dispensing on gold nanofoam. The total energy spectra obtained from both sources are compared with each other, and the measured fractional electron capture probabilities are compared with those available in the literature and from the BetaShape code. [ABSTRACT FROM AUTHOR]

Recent advances in the development of cryogenic particle detectors such as magnetic microcalorimeters allow the fabrication of sensor arrays with an increasing number of pixels. Since these detectors must be operated at the lowest temperatures, the readout of large detector arrays is still quite challenging. This is especially true for the ECHo experiment, which presently aims to simultaneously run 6,000 two pixel detectors to investigate the electron neutrino mass. For this reason, we developed a readout system based on a microwave SQUID multiplexer (μ MUX) that is operated by a custom software-defined radio (SDR) at room-temperature. The SDR readout electronics consist of three distinct hardware units: a data processing board with a Xilinx ZynqUS+ MPSoC; a converter board that features DACs, ADCs, and a coherent clock distribution network; and a radio frequency front-end board to translate the signals between the baseband and the microwave domains. Here, we describe the characteristics of the full-scale SDR system. First, the generated frequency comb for driving the μ MUX was evaluated. Subsequently, by operating the SDR in direct loopback, the crosstalk of the individual channels after frequency demultiplexing was investigated. Finally, the system was used with a 16-channel μ MUX to evaluate the linearity of the SDR, and the noise contributed to the overall readout setup. [ABSTRACT FROM AUTHOR]

In the last years, the COSINUS (Cryogenic Observatory for SIgnals seen in Next generation Underground Searches) experiment has made significant progress both in the construction of its facility and in pursuing its physics goals: At Laboratori Nazionali del Gran Sasso (LNGS) in Italy, an underground facility was constructed, which will house experimental detectors for dark matter direct detection in a dry dilution cryostat. Construction of the main structures at the COSINUS site is finished, including the control building, the cryostat access level, and the water tank which will serve as a Cherenkov muon veto around the cryostat. With a nuclear recoil threshold of 4 keV, the latest COSINUS detector prototype approaches the design goal of 1 keV, and particle discrimination on event-by-event basis has been demonstrated. This contribution gives a brief overview on the status of COSINUS. [ABSTRACT FROM AUTHOR]

We describe a technique to optimize the dynamic performance of microwave SQUID multiplexer (µMUX)-based systems. These systems proved to be adequate for reading out multiple cryogenic detectors simultaneously. However, the requirement for denser detector arrays to increase the sensitivity of scientific experiments makes its design a challenge. When modifying the readout power, there is a trade-off between decreasing the signal-to-noise ratio (SNR) and boosting the nonlinearities of the active devices. The latter is characterized by the spurious free dynamic range (SFDR) parameter and manifests as an increment in the intermodulation products and harmonics power. We estimate the optimal spectral location of the SQUID signal containing the detector information for different channels. Through the technique, what we refer to as Spectral Engineering, it is possible to minimize the SNR degradation while maximizing the SFDR of the detector signal, thus, overcoming the trade-off. [ABSTRACT FROM AUTHOR]

The AnaBHEL experiment aims to detect the analog Hawking radiation emitted by an accelerated relativistic plasma mirror for which the effective event horizon is analogous to that of a black hole, thanks to the equivalence principle. This radiation is composed of a few Hawking photons emitted simultaneously in the infrared band and the 'partner photons' in the ultraviolet band. The former is emitted in the opposite direction of the mirror propagation and is redshifted in the laboratory frame. In the AnaBHEL scheme, high-intensity petawatt laser pulses, will be used to produce the relativistic accelerated plasma mirrors from a helium gas jet. Infrared and ultraviolet photons generated by the mirrors will be detected by dedicated superconducting nanowire single-photon detectors (SNSPDs) at very low temperature and by multichannel plates at room temperature, respectively. Details of the setup design are discussed. [ABSTRACT FROM AUTHOR]

A novel system formed by a Microwave Superconducting Quantum Interference Device (SQUID) Multiplexer (μ MUX) and a room temperature electronics employs frequency division multiplexing (FDM) technique to read out multiple cryogenic detectors. Since the detector signal is embedded in the phase of the SQUID signal, a Digital Quadrature Demodulator (DQD) is widely implemented to recover it. However, the DQD also generates a signal that aliases into the first Nyquist zone affecting the demodulated detector signal. In this work, we demonstrate how this spurious signal is generated and a mathematical model of it is derived and validated. In addition, we discuss different proposals to improve the attenuation of this undesired signal. Lastly, we implement one of the proposals in our readout system. Our measurements show an enhancement in the spurious signal attenuation of more than 35 dB. As a result, this work contributes to attenuate the spurious below the system noise. [ABSTRACT FROM AUTHOR]

The EDELWEISS collaboration aims for direct detection of light dark matter using germanium cryogenic detectors with low threshold phonon sensor technologies and efficient charge readout designs. We describe here the development of Ge bolometers equipped with high impedance thermistors based on a NbxSi1−x TES alloy. High aspect ratio spiral designs allow the TES impedance to match with JFET or HEMT front-end amplifiers. We detail the behavior of the superconducting transition properties of these sensors and the detector optimization in terms of sensitivity to a-thermal phonons. We report preliminary results of a 200 g Ge detector that was calibrated using 71Ge activation by neutrons at the LSM underground laboratory. [ABSTRACT FROM AUTHOR]

Fractional electron capture probability ratios of 125I were measured using metallic magnetic calorimeters (MMCs). Due to the 4π geometry of the source embedded in the absorber, detection efficiency of nearly 99% was observed for K, L, M, and N capture events. The fractional capture probabilities were calculated from peak area ratios. [ABSTRACT FROM AUTHOR]

The Ricochet reactor neutrino observatory is planned to be installed at the Laue Langevin Institute starting mid-2022. Its scientific goal is to perform a low-energy and high precision measurement of the coherent elastic neutrino-nucleus scattering spectrum in order to explore exotic physics scenarios. Ricochet will host two cryogenic detector arrays: the CryoCube (Ge target) and the Q-array (Zn target), operated at 10 mK. The 1 kg Ge CryoCube will consist of 27 Ge crystals instrumented with NTD-Ge thermal sensors and charge collection electrodes for a simultaneous heat and ionization readout to reject the electromagnetic backgrounds (gamma, beta, x-rays). We present the status of its front-end electronics. The first stage of amplification is made of High Electron Mobility Transistors developed by CNRS/C2N laboratory, optimized to achieve ultra-low noise performance at 1 K with a dissipation as low as 15 μ W per channel. Our noise model predicts that 10 eV heat and 20 eV ee RMS baseline resolutions are feasible with a high dynamic range for the deposited energy (up to 10 MeV) thanks to loop amplification schemes. Such resolutions are mandatory to have a high discrimination power between nuclear and electron recoils at the lowest energies. [ABSTRACT FROM AUTHOR]

Extended X-ray absorption fine structure (EXAFS) spectroscopy is a powerful technique that gives element-specific information about the structure of molecules. The development of a laboratory EXAFS spectrometer capable of measuring transmission spectra would be a significant advance as the technique is currently only available at synchrotron radiation lightsources. Here, we explore the potential of cryogenic detectors as the energy-resolving component of a laboratory transmission EXAFS instrument. We examine the energy resolution, count rate, and detector stability needed for good EXAFS spectra and compare these to the properties of cryogenic detectors and conventional X-ray optics. We find that superconducting tunnel junction detectors are well-suited for this application. [ABSTRACT FROM AUTHOR]

Searches for dark matter with cryogenic detectors are pushing to lower energy thresholds at each development stage. Consequently, new approaches for detector calibration at the proposed energy scales are necessary. In the case of SuperCDMS SNOLAB, energy thresholds in the range of a few eV are expected. In this paper, we are reporting R&D work for new ideas to calibrate cryogenic detectors in the eV range utilizing LEDs of various wavelengths operated at cryogenic temperatures. [ABSTRACT FROM AUTHOR]

QUBIC is a ground-based experiment aiming to measure the B-mode polarization of the cosmic microwave background. The developed instrument is an innovative two-frequency band bolometric interferometer that will operate at 300 mK with NbSi TES arrays. In this paper, we describe the fabrication process of the detectors. [ABSTRACT FROM AUTHOR]

We present the noise performance of high electron mobility transistors (HEMT) developed by CNRS/C2N laboratory. Various HEMT's gate geometries with 2 pF to 230 pF input capacitance have been studied at 4 K. A model for both voltage and current noises has been developed with frequency dependence up to 1 MHz. These HEMTs exhibit low dissipation, excellent noise performance and can advantageously replace traditional Si-JFETs for the readout of high impedance thermal sensor and semiconductor ionization cryogenic detectors. Our model predicts that cryogenic germanium detectors of 30 g with 10 eV heat and 20 eV ee baseline resolution are feasible if read out by HEMT-based amplifiers. Such resolution allows for high discrimination between nuclear and electron recoils at low threshold. This capability is of major interest for coherent elastic neutrino scattering and low-mass dark matter experiments such as Ricochet and EDELWEISS. [ABSTRACT FROM AUTHOR]

Cryogenic Rare Event Search with Superconducting Thermometers (CRESST) is a long-standing direct dark matter detection experiment with cryogenic detectors located at the underground facility Laboratori Nazionali del Gran Sasso in Italy. CRESST-III, the third generation of CRESST, was specifically designed to have a world-leading sensitivity for low-mass dark matter (DM) (less than 2 GeV/ c 2 ) to probe the spin-independent DM-nucleus cross section. At present, a large part of the parameter space for spin-independent scattering off nuclei remains untested for dark matter particles with masses below few GeV/ c 2 although many motivated theoretical models having been proposed. The CRESST-III experiment employs scintillating CaWO 4 crystals of ∼ 25 g as target material for dark matter interactions operated as cryogenic scintillating calorimeters at ∼ 10 mK. CRESST-III first data taking was successfully completed in 2018, achieving an unprecedented energy threshold for nuclear recoils. This result extended the present sensitivity to DM particles as light as ∼ 160 MeV/ c 2 . In this paper, an overview of the CRESST-III detectors and results will be presented. [ABSTRACT FROM AUTHOR]

We present a strip transition-edge sensor microcalorimeter linear array detector developed for energy dispersive X-ray diffraction imaging and Compton scattering applications. The prototype detector is an array of 20 transition-edge sensors with absorbers in strip geometry arranged in a linear array. We discuss the fabrication steps needed to develop this array including Mo/Cu bilayer, Au electroplating, and proof-of-principle fabrication of long strips of SiN x membranes. We demonstrate minimal unwanted effect of strip geometry on X-ray pulse response and show linear relationship of 1/pulse height and pulse decay times with absorber length. For the absorber lengths studied, our preliminary measurements show energy resolutions of 40–180 eV near 17 keV. Furthermore, we show that the heat flow to the cold bath is nearly independent of the absorber area and depends on the SiN x membrane geometry. [ABSTRACT FROM AUTHOR]

The Super Cryogenic Dark Matter Search is one of the leading experiments in the direct search for weakly interacting massive particles in the mass range below 10 GeV/c2. Particles are detected in cryogenic semiconductor detectors; their energy deposition produces phonons and liberates charges which are measured in TES-based phonon sensors and charge-collecting electrodes. The next generation of the experiment will be deployed at SNOLAB and aims to further reduce the detection threshold to a few tens of eV by reducing the noise in the readout circuit and improving the design of the phonon sensors. Traditionally, radioactive sources are used to calibrate the energy scale and to monitor detector stability. However, in most cases, it takes a long time to accumulate enough events to identify peaks in the energy spectrum. Moreover, gammas of low energy as would be required to calibrate the bottom range of the detector’s energy range cannot penetrate the cryostat shielding. This study investigates the possibility of using pulsed infrared LEDs mounted inside the cryostat as alternative calibration source. [ABSTRACT FROM AUTHOR]

The EDELWEISS collaboration is performing a direct search for WIMP dark matter using an array of up to twenty-four 820-890 g cryogenic germanium detectors equipped with a full charge and thermal signal readout. The experiment is located in the ultra-low-radioactivity background environment of the Modane underground laboratory, in the French-Italian Fréjus tunnel. We present the analysis of data obtained in extended data taking periods. WIMP limits, background rejection factors and measurements of cosmogenic activation are used to assess the performance of the third generation of EDELWEISS detectors in view of the search for WIMPs in the mass range from 1 to 20GeV/c2. The developments in progress to pursue this goal in the coming years are also presented. [ABSTRACT FROM AUTHOR]

The Physics Department of the Technical University of Munich operates a shallow underground detector laboratory in Garching, Germany. It provides ∼160m2 of laboratory space which is shielded from cosmic radiation by ∼6m of gravel and soil, corresponding to a shielding of ∼15m.w.e.. The laboratory also houses a cleanroom equipped with work- and wetbenches, a chemical fumehood as well as a spin-coater and a mask-aligner for photolithographic processing of semiconductor detectors. Furthermore, the shallow underground laboratory runs two high-purity germanium detector screening stations, a liquid argon cryostat and a 3He-4He dilution refrigerator with a base temperature of ≤12-14mK. The infrastructure provided by the shallow laboratory is particularly relevant for the characterization of CaWO4 target crystals for the CRESST-III experiment, detector fabrication and assembly for rare event searches. Future applications of the laboratory include detector development in the framework of coherent neutrino nucleus scattering experiments (ν-cleus) and studying its potential as a site to search for MeV-scale dark matter with gram-scale cryogenic detectors. [ABSTRACT FROM AUTHOR]

The CRESST-III experiment (Cryogenic Rare Events Search with Superconducting Thermometers), located at the underground facility Laboratori Nazionali del Gran Sasso in Italy, uses scintillating CaWO4 crystals as cryogenic calorimeters to search for direct dark matter interactions in detectors. A large part of the parameter space for spin-independent scattering off nuclei remains untested for dark matter particles with masses below a few GeV/c2, despite many naturally motivated theoretical models for light dark matter particles. The CRESST-III detectors are designed to achieve the performance required to probe the low-mass region of the parameter space with a sensitivity never reached before. In this paper, new results on the performance and an overview of the CRESST-III detectors will be presented, emphasizing the results about the low-energy threshold for nuclear recoil of CRESST-III Phase 1 which started collecting data in August 2016. [ABSTRACT FROM AUTHOR]

We report on the fabrication and characterization of Mo/Au-based transition-edge sensors (TES), intended to be used in X-ray detectors. We have performed complete dark characterization using I-V curves, complex impedance and noise measurements at different bath temperatures and biases. Devices with two designs, different sizes and different membranes have been characterized, some of them with a central bismuth absorber. This has allowed extraction of the relevant parameters of the TES, analyses of their standard behavior and evaluation of their prospects. [ABSTRACT FROM AUTHOR]

EDELWEISS-III is a direct dark matter search experiment, running 800 g heat-and-ionization cryogenic germanium detectors equipped with Full InterDigitized electrodes (FID) for the rejection of near-surface events. We report a preliminary analysis for a subset of the data (35 kg $$\cdot $$ days) as well as future prospects for low-mass WIMPs seach. [ABSTRACT FROM AUTHOR]

SRON is developing ultra-low-noise transition edge sensors (TESs) based on a superconducting Ti/Au bilayer on a suspended SiN island with SiN legs for SAFARI aboard SPICA. We have two major concerns about realizing TESs with an ultra-low NEP of $$2\times 10^{-19}~\hbox {W}/\sqrt{{\text {Hz}}}$$ : achieving lower thermal conductance and no excess noise with respect to the phonon noise. To realize TESs with phonon-noise-limited NEPs, we need to make thinner ( $${<}0.25~\upmu \hbox {m}$$ ) and narrower ( $${<}1~\upmu \hbox {m}$$ ) SiN legs. With deep reactive-ion etching, three types of TESs were fabricated in combination with different SiN island sizes and the presence or absence of an optical absorber. Those TESs have a thin $$(0.20~\upmu \hbox {m}$$ ), narrow (0.5-0.7 $$\upmu \hbox {m}$$ ), and long (340-460 $$\upmu \hbox {m}$$ ) SiN legs and show $$T_{\mathrm {c}}$$ of $${\sim }93~\hbox {mK}$$ and $$R_{\mathrm {n}}$$ of $${\sim }158~\hbox {m}{\Omega }$$ . These TESs were characterized under AC bias using our frequency-division multiplexing readout (1-3 MHz) system. TESs without the absorber show NEPs as low as $$1.1\,\times \,10^{-19}~\hbox {W}/\sqrt{{\text {Hz}}}$$ with a reasonable response speed ( $${<}1~\hbox {ms}$$ ), which achieved the phonon noise limit. For TESs with the absorber, we confirmed a higher $$\hbox {NEP}_{\mathrm {el}} ({\sim }5\,\times \,10^{-19}~\hbox {W}/\sqrt{{\text {Hz}}}$$ ) than that of TESs without the absorber likely due to stray light. The lowest NEP can make the new version of SAFARI with a grating spectrometer feasible. [ABSTRACT FROM AUTHOR]

There is a common need in astroparticle experiments such as direct dark matter detection, double-beta decay without emission of neutrinos [ $$0 \nu \beta \beta $$ ] and coherent neutrino nucleus scattering experiments for light detectors with a very low energy threshold. By employing the Neganov-Trofimov-Luke Effect, the thermal signal of particle interactions in a semiconductor absorber operated at cryogenic temperatures can be amplified by drifting the photogenerated electrons and holes in an electric field. This technology is not used in current experiments, in particular because of a reduction of the signal amplitude with time which is due to trapping of the charges within the absorber. We present here the first results of a novel type of Neganov-Trofimov-Luke Effect light detector with an electric field configuration designed to improve the charge collection within the semiconductor. [ABSTRACT FROM AUTHOR]

The increasing sensitivity of high impedance cryogenic detectors demands amplification stages closer to detectors to guarantee high performance. We have developed a cryogenic installation to measure the intrinsic noise, the gain, and the DC characteristics of HEMTs or MOSFETs at low temperature. Components under test are mounted in a helium cryostat containing a double stage $$^{3}$$ He/ $$^{4}$$ He sorption cooler to perform sub-kelvin measurements. In this work, we describe this installation and present the encouraging first results that have revealed a level of intrinsic input voltage noise of a HEMT, developed by CNRS/LPN, of 0.44 nV/sqrt(Hz) at 1 kHz at 480 mK (Cin $$=$$ 100 pF). [ABSTRACT FROM AUTHOR]

The main low temperature detectors (LTD) applications and results of LTD in fundamental physics will be considered with particular reference to the nuclear and subnuclear fields. The results obtained with cryogenic techniques and in particularly those with the hybrid ones where bolometers are operated in coincidence or anticoincidence with scintillation or semiconductor detectors will be reported and discussed. In particular the paper will refer to the results and plans in the direct determination of the neutrino mass. In connection with this subject we will review the already obtained and planned results of experiments on neutrinoless double beta decay to reveal the possible violation of the lepton number with the consequent determination or constraint on the neutrino mass. The present and future impact of low temperature techniques in direct detection of Weakly Interacting Massive Particles will be discussed in comparison with the present and future experiments with 'classical' detectors. The report will be concluded by the present few and hopefully more numerous future results on the application of low temperature detectors on rare events in low energy nuclear physics. [ABSTRACT FROM AUTHOR]

The SuperCDMS collaboration is presently operating a 9 kg Ge payload at the Soudan Underground Laboratory in their direct search for dark matter. The Ge detectors utilize double-sided athermal phonon sensors with an interdigitated electrode structure (iZIPs) to reject near-surface electron-recoil events. These detectors each have a mass of 0.6 kg and were fabricated with photolithographic techniques. The detector fabrication advances required and the production yield encountered are described. [ABSTRACT FROM AUTHOR]

SRON is developing TES detectors based on a superconducting Ti/Au bilayer on a suspended SiN membrane for the short-wavelength band of the SAFARI instrument on SPICA mission. We have recently replaced the wet KOH etching of the Si substrate by deep reactive ion etching. The new process enables us to fabricate the detectors on the substrate and release the membrane at the very last step. Therefore the production of SAFARI large arrays (43 $$\,{\times }\,$$ 43) on thin SiN membrane (250 nm) is feasible. It also makes it possible to realize narrow supporting SiN legs of $$\le $$ 1 $$\upmu $$ m, which are needed to meet SAFARI NEP requirements. Here we report the current-voltage characteristics, noise performance and impedance measurement of these devices. The measured results are then compared with the distributed leg model that takes into account the thermal fluctuation noise due to the SiN legs. We measured a dark NEP of $$\sim $$ 0.7 aW/ $$\sqrt{\hbox {Hz}}$$ , which is 1.6 times higher than the theoretically expected phonon noise. [ABSTRACT FROM AUTHOR]

We report the final results of EDELWEISS-II, obtained with ten 400 g heat-and-ionization cryogenic detectors equipped with InterDigit electrodes for the rejection of near-surface events. Results from fourteen months of continuous operation and a total exposure of 384 kg day are presented. We also present the status of EDELWEISS-III, which will accumulate more than 3000 kg day of data with 40 new 800 g detectors in the coming years. [ABSTRACT FROM AUTHOR]

The direct detection of the Universe's Dark Matter is one of the key questions in particle astrophysics. Cryogenic based detectors offer advantages in low radioactive backgrounds, target mass, sensitivity to the small energy depositions and rejection of possible background sources. I will summarize the main experimental approaches, including both cryogenic crystal and liquid targets and the options pursued for their signal readout. Recent advances from around the world and prospects for future proposed experiments will be discussed. [ABSTRACT FROM AUTHOR]

We report the recent progress in the development of decay energy spectroscopy for radionuclide analysis using a metallic magnetic calorimeter. In the present analysis, sample radionuclides were completely enclosed by a 4 π steradian absorber. The use of a 4 π absorber composed of gold foil guarantees that the total energy associated with radioactive decay is converted into thermal energy in the absorber. A paramagnetic temperature sensor was attached to the absorber to accurately measure the temperature change due to radioactive decay. The plutonium isotopes Pu, Pu, and Pu were readily identified in the decay energy spectrum because each isotope creates a single peak at its characteristic Q value. Two clear peaks were observed for Pu and Pu, and a 6.3 keV FWHM was obtained. The energy resolution of the method was affected by the low-energy tail of the spectrum at the left-hand side of the peaks. A 4.1 keV FWHM of a Gaussian fit was obtained for the right-hand side of the peak. Slow heat release to the absorber due to heat flow mechanisms is discussed to explain the low-energy tailing effect. [ABSTRACT FROM AUTHOR]

We report on precise drift velocity measurements of electrons and holes in 50 mK, ultrapure (≈10 net shallow impurities per cm) germanium 〈100〉 CDMS dark matter detectors as a function of electric field up to 4 V/cm. A laser diode connected to an optical fiber extending from room-temperature to the detector creates electron-hole pairs on one surface of the crystal. High-speed electronics measure the drift current as the generated carriers travel to the opposite face of the crystal. CDMS detectors measure the ionization and phonon response of particle interactions within the crystal. Stable charge collection is necessary for successful background discrimination when looking for a possible dark matter signal. While biased, however, ionization performance degrades over time due to the build-up of space charge. Free electrons and holes created by particle interactions are subject to drift-diffusion dynamics occurring simultaneously with the trapping of carriers to localized surface and bulk states. The combination of these processes determine the evolution of space charge within the crystal, making it important that we understand carrier transport under our unique operating condition of low-temperature and low-field. We find good agreement between our measured drift velocities and our theoretical predictions, indicating carrier scattering is dominated by spontaneous phonon emission. In addition, we present preliminary measurements of effective longitudinal carrier trapping lengths for both n-type and p-type crystals at 50 mK. [ABSTRACT FROM AUTHOR]

We present new results on the development of larger arrays (presently 72 channels, goal of multiple units of 160 channels) of superconducting LC filters. The a-Si:H based resonators show a quality factor above 10.000. The latest design utilizes oppositely wound planar coil pairs which enable close packing with low magnetic cross talk. We present results on the obtained center frequency distribution within the range of 1 to 3 MHz. [ABSTRACT FROM AUTHOR]

We report the recent progress on high resolution alpha spectrometers that use metallic magnetic calorimeters. The detector is composed of a meander-type magnetic calorimeter and a gold-foil absorber. The thermal connection between the magnetic sensor and the absorber consists of annealed gold wires. The signal rise time is found to be as expected, with the electronic thermal conductance of gold wires. The energy resolution of a 3.2 keV FWHM is obtained for 5.5 MeV alpha particles with possibilities for further improvements. [ABSTRACT FROM AUTHOR]

Transition edge sensors (TES) are the chosen detector technology for the SAFARI imaging spectrometer on the SPICA telescope. The TES are required to have an NEP of $2\mbox{--}3\times 10^{-19}~\mbox{W/}\sqrt{\mathrm{Hz}}$ to take full advantage of the cooled mirror. SRON has developed TiAu TES bolometers for the short wavelength band (30-60 μm). The TES are on SiN membranes, in which long and narrow legs act as thermal links between the TES and the bath. We present a distributed model that accounts for the heat conductance and the heat capacity in the long legs that provides a guideline for designing low noise detectors. We report our latest results that include a measured dark NEP of $4.2\times 10^{-19}~\mbox{W/}\sqrt{\mathrm{Hz}}$ and a saturation power of about 10 fW. [ABSTRACT FROM AUTHOR]

A novel type of absorber, dedicated to cryogenic detectors, was conceived to reach a high and constant intrinsic detection efficiency (>98%) for up to 25 keV X-ray photons. The absorber consists of two layers having a different atomic number Z. The role of the first layer (large Z) is to make negligible the transmission through the absorber; while the second layer (medium Z) has to reabsorb the escape photons from the first layer. A metallic magnetic calorimeter was realized with an Au-Ag absorber. The required thicknesses of both layers were determined using Monte Carlo simulation of the efficiency. To show the advantages of such a detector, its efficiency and its energy resolution are compared to the efficiency and energy resolution of a gold absorber using a Am source. [ABSTRACT FROM AUTHOR]