Search

Coherent elastic neutrino-nucleus scattering (CE ν NS), detected for the first time more than 40 years after its prediction, represents an experimental challenge because of its signature: a single nuclear recoil with energy in the range of 10 eV to a few 10's keV on average. One of the main features of CE ν NS is its cross section, around two orders of magnitude higher compared with the inverse β decay. BASKET (Bolometers At Sub keV Energy Threshold) project aims at investigating cryogenic calorimeters for the CE ν NS detection, able to maintain the background level below the expected signature while being operated in above ground conditions in close vicinity to a nuclear reactor. The main requirements for such detectors are a low enough energy threshold of O(10 eV), and a fast signal rise time in the range of 0.1–1 ms to achieve good timing resolution and hence good mitigation of pile-up events. In this article, we report on the first tests of a prototype detector coupling a Li 2 WO 4 crystal to a magnetic metallic calorimeter (MMC) thermal sensor. [ABSTRACT FROM AUTHOR]

BINGO is a project aiming to set the grounds for large-scale bolometric neutrinoless double-beta-decay experiments capable of investigating the effective Majorana neutrino mass at a few meV level. It focuses on developing innovative technologies (a detector assembly, cryogenic photodetectors and active veto) to achieve a very low background index, of the order of 1 0 − 5 counts/(keV kg yr) in the region of interest. The BINGO demonstrator, called MINI-BINGO, is designed to investigate the promising double-beta-decay isotopes 100Mo and 130Te and it will be composed of Li 2 MoO 4 and TeO 2 crystals coupled to bolometric light detectors and surrounded by a Bi 4 Ge 3 O 12 -based veto. This will allow us to reject a significant background in bolometers caused by surface contamination from α -active radionuclides by means of light yield selection and to mitigate other sources of background, such as surface contamination from β -active radionuclides, external γ radioactivity, and pile-up due to random coincidence of background events. This paper describes an R&D program towards the BINGO goals, particularly focusing on the development of an innovative assembly designed to reduce the passive materials within the line of sight of the detectors, which is expected to be a dominant source of background in next-generation bolometric experiments. We present the performance of two prototype modules – housing four cubic (4.5-cm side) Li 2 MoO 4 crystals in total – operated in the Canfranc underground laboratory in Spain within a facility developed for the CROSS double-beta-decay experiment. [ABSTRACT FROM AUTHOR]

The determination of the absolute mass scale of neutrinos is one of the most important challenges in Particle Physics. The shape of the endpoint region of β - -decay and electron capture (EC) spectra depends on the phase space factor, which, in turn, is function of the masses of the neutrino mass eigenstates. High energy resolution and high statistics measurements of β - and EC spectra are therefore considered a model-independent way for the determination of the neutrino mass scale. Since almost four decades, low temperature microcalorimeters are used for the measurement of low energy β - and EC spectra. The first efforts were focused on the development of large arrays for the measurement of the 187 Re β - -spectrum. In the last ten years, the attention moved to EC of 163 Ho. This choice was mainly motivated by the very good performance which could be achieved with low temperature microcalorimeters enclosing 163 Ho with respect to microcalorimeters with absorber containing 187 Re. The development of low temperature microcalorimeters for the measurement of the finite neutrino mass is discussed and, in particular, the reasons for moving from 187 Re to 163 Ho. The possibility to reach sub-eV sensitivity on the effective electron neutrino mass with 163 Ho, thanks to the multiplexing of large microcalorimeter arrays is demonstrated. In conclusion, an overview on other nuclides which have been proposed as good candidates, motivated by the excellent performance of low temperature microcalorimeters is presented. [ABSTRACT FROM AUTHOR]

The state-of-the-art technology of X-ray microcalorimeters based on superconducting transition-edge sensors (TESs), for applications in astrophysics and particle physics, is reviewed. We will show the advance in understanding the detector physics and describe the recent breakthroughs in the TES design that are opening the way towards the fabrication and the read-out of very large arrays of pixels with unprecedented energy resolution. The most challenging low temperature instruments for space- and ground-base experiments will be described. [ABSTRACT FROM AUTHOR]

In recent years Microwave Kinetic Inductance Detectors (MKIDs) have emerged as one of the most promising novel low temperature detector technologies. Their unrivaled scalability makes them very attractive for many modern applications and scientific instruments. In this paper we intend to give an overview of how and where MKIDs are currently being used or are suggested to be used in the future. MKID based projects are ongoing or proposed for observational astronomy, particle physics, material science and THz imaging, and the goal of this review is to provide an easily usable and thorough list of possible starting points for more in-depth literature research on the many areas profiting from kinetic inductance detectors. [ABSTRACT FROM AUTHOR]

We developed measurement systems for the simultaneous detection of phonon and scintillation signals from Li 2 MoO 4 crystals based on the metallic magnetic calorimeter (MMC) technology. Two measurements were carried out using Li 2 MoO 4 crystals of different sizes. The first measurement was conducted with a compact detection system designed for a 1 × 1 × 1 cm 3 crystal. An advanced light detector with Neganov–Luke phonon amplification was adopted in the compact setup. Later, the second experiment was carried out using a cylindrical Li 2 MoO 4 crystal of 5 cm in diameter and 5 cm in height. Another light detector was implemented with a 2-in. Ge wafer and an MMC sensor. Both measurements resulted in simultaneous detection of heat and light signals. Clear particle discriminations between α - and β / γ -induced events were demonstrated by comparing amplitudes of the heat and light signals in both measurements. The heat signals in the larger setup showed an energy resolution of 18 keV FWHM for 2615 keV γ -rays. The energy linearity of the detector response was investigated for a suitable calibration near 3.034 MeV, the Q value of 100 Mo double-beta decay. [ABSTRACT FROM AUTHOR]

The state-of-the-art technology of X-ray microcalorimeters based on superconducting transition-edge sensors (TESs), for applications in astrophysics and particle physics, is reviewed. We will show the advance in understanding the detector physics and describe the recent breakthroughs in the TES design that are opening the way towards the fabrication and the read-out of very large arrays of pixels with unprecedented energy resolution. The most challenging low temperature instruments for space- and ground-base experiments will be described.

Abstract The semimetal character of bismuth and its large photon absorbing power make of this element the most suitable absorber material for X-ray low temperature detectors. This application requires coatings of Bi with thicknesses and properties that only electrodeposition methods may achieve. Although there are studies on electrodeposition of bismuth for these detectors and other devices, the process is not straightforward and has not been sufficiently studied in terms of the desired final properties, neither the effect of different parameters is well known or easily reproduced. This work reports the influence of two different electrolytes, of the deposition method, and of heating and stirring on the structure, microstructure and transport properties of bismuth films. Typically, rhombohedral Bi is obtained upon electrodeposition with very good crystallinity, and some crystal preferential orientation, while significant empirical correlations are found among electrochemical parameters, microstructure, and resistivity. Such correlation allows the identification of the deposition parameters for coatings that yield the optimal functional properties. Highlights • Electrodeposition electrolyte and conditions clearly influence Bi films structure and microstructure. • Bi films microstructure is determinant for Bi films resistivity behavior. • Films with best resistivity are obtained with the electrolyte containing additives. • Resistivity data obtained are similar to bulk Bi of similar thicknesses. [ABSTRACT FROM AUTHOR]

In recent years Microwave Kinetic Inductance Detectors (MKIDs) have emerged as one of the most promising novel low temperature detector technologies. Their unrivaled scalability makes them very attractive for many modern applications and scientific instruments. In this paper we intend to give an overview of how and where MKIDs are currently being used or are suggested to be used in the future. MKID based projects are ongoing or proposed for observational astronomy, particle physics, material science and THz imaging, and the goal of this review is to provide an easily usable and thorough list of possible starting points for more in-depth literature research on the many areas profiting from kinetic inductance detectors.

Bolometers are cryogenic calorimeters which feature excellent energy resolution, low energy threshold, high detection efficiency, flexibility in choice of materials, particle identification capability if operated as hybrid devices. After 30 years of rapid progresses, they represent nowadays a leading technology in several fields: particle and nuclear physics, X-ray astrophysics, cosmology. However, further and substantial developments are required to increase the sensitivity to the levels envisioned by future researches. A review of the challenges to be addressed and potentialities of bolometers in the search for rare nuclear decays is given, with particular emphasis to the neutrinoless double beta decay physics case. [ABSTRACT FROM AUTHOR]

We have developed large-format, close-packed X-ray microcalorimeter arrays fabricated on solid substrates, designed to achieve high energy resolution with count rates up to a few hundred counts per second per pixel for X-ray photon energies up to 8 keV. Our most recent arrays feature 31-micron absorbers on a 35-micron pitch, reducing the size of pixels by about a factor of two. This change will enable an instrument with significantly higher angular resolution. In order to wire out large format arrays with an increased density of smaller pixels, we have reduced the lateral size of both the microstrip wiring and the Mo/Au transition-edge sensors (TES). We report on the key physical properties of these small TESs and the fine Nb leads attached, including the critical currents and weak-link properties associated with the longitudinal proximity effect. [ABSTRACT FROM PUBLISHER]

We develop superconducting transition-edge sensor (TES) microcalorimeter focal planes for versatility in meeting the specifications of X-ray imaging spectrometers, including high count rate, high energy resolution, and large field of view. In particular, a focal plane composed of two subarrays: one of fine pitch, high count-rate devices and the other of slower, larger pixels with similar energy resolution, offers promise for the next generation of astrophysics instruments, such as the X-ray Integral Field Unit Instrument on the European Space Agency's ATHENA mission. We have based the subarrays of our current design on successful pixel designs that have been demonstrated separately. Pixels with an all-gold X-ray absorber on 50 and 75 μm pitch, where the Mo/Au TES sits atop a thick metal heatsinking layer, have shown high resolution and can accommodate high count rates. The demonstrated larger pixels use a silicon nitride membrane for thermal isolation, thinner Au, and an added bismuth layer in a 250-μm2 absorber. To tune the parameters of each subarray requires merging the fabrication processes of the two detector types. We present the fabrication process for dual production of different X-ray absorbers on the same substrate, thick Au on the small pixels and thinner Au with a Bi capping layer on the larger pixels to tune their heat capacities. The process requires multiple electroplating and etching steps, but the absorbers are defined in a single-ion milling step. We demonstrate methods for integrating the heatsinking of the two types of pixel into the same focal plane consistent with the requirements for each subarray, including the limiting of thermal crosstalk. We also discuss fabrication process modifications for tuning the intrinsic transition temperature ( Tc) of the bilayers for the different device types through variation of the bilayer thicknesses. The latest results on these “hybrid” arrays will be presented. [ABSTRACT FROM PUBLISHER]

A new experimental system for precise determination of electronic stopping powers of heavy ions has been set up at the accelerator laboratory of the University of Jyväskylä. The new setup, combining an established B-ToF system and an array of calorimetric low temperature detectors (CLTDs), has been used for the determination of electronic stopping powers of 0.05–1 MeV/u 131 Xe ions in carbon, nickel and gold. Thereby advantage of the improved linearity and energy resolution of CLTDs as compared to the previously used ionization detector was taken to reduce energy calibration errors and to increase sensitivity for the energy loss determination, in particular at very low energies. The total uncertainties of 3–4% for C- and Ni-targets, and 5–7% for Au-targets, respectively, are dominated by the target properties, i.e. thickness determination and inhomogeneities. The results are compared to data from literature and to predictions of different theoretical computer codes. In the high energy part of the examined energy range the results are in good agreement with previously published data, while new stopping power data for very heavy ions in different Z 2 -materials have been obtained at lower energies. Moreover, unexpectedly strong channeling effects for the transmission of the 131 Xe ions in thin, partly polycrystalline nickel and gold target foils have been observed and investigated. [ABSTRACT FROM AUTHOR]

HOLMES is an ERC project started in 2014 that will perform a model independent measurement of the neutrino mass with a sensitivity of the order of 1 eV. In order to reach its goal sensitivity, HOLMES will use 1000 low temperature microcalorimeters, each implanted with an activity of 300 Bq of 163Ho, performing thus a calorimetric measurement. This contribution presents the recent results achieved that lay the grounds for the low-activity phase of the HOLMES experiment, that will lead to its first limit on the neutrino mass. [ABSTRACT FROM AUTHOR]

Calorimetric low temperature detectors (CLTD's) for heavy-ion detection have been combined with the LOHENGRIN recoil separator at the ILL Grenoble for the determination of nuclear charge distributions of fission fragments produced by thermal neutron-induced fission of $$^{235}$$ U. The LOHENGRIN spectrometer separates fission fragments according to their mass-to-ionic-charge ratio and their kinetic energy, but has no selectivity with respect to nuclear charges Z. For the separation of the nuclear charges, one can exploit the nuclear charge-dependent energy loss of the fragments passing through an energy degrader foil (absorber method). This separation requires detector systems with high energy resolution and negligible pulse height defect, as well as degrader foils which are optimized with respect to thickness, homogeneity, and energy loss straggling. In the present, contribution results of test measurements at the Maier Leibnitz tandem accelerator facility in Munich with $$^{109}$$ Ag and $$^{127}$$ I beams with the aim to determine the most suitable degrader material, as well as measurements at the Institut Laue-Langevin will be presented. These include a systematic study of the quality of Z-separation of fission fragments in the mass range $$82\le A \le 132$$ and a systematic measurement of $$^{92}$$ Rb fission yields, as well as investigations of fission yields toward the symmetry region. [ABSTRACT FROM AUTHOR]

For future X-ray observatories utilizing transition-edge sensor (TES) microcalorimeters, an anti-coincidence detector (anti-co) is required to discriminate X-ray ( $$\sim $$ 0.1-10 keV) signals from non-X-ray background events, such as ionizing particles. We have developed a prototype anti-co that utilizes TESs, which will be compatible with the TES focal-plane arrays planned for future X-ray observatories. This anti-co is based upon the cryogenic dark matter search II detector design. It is a silicon wafer covered with superconducting collection fins and TES microcalorimeters. Minimum ionizing particles deposit energy while passing through the silicon. The athermal phonons produced by these events are absorbed in the superconducting fins, breaking Cooper pairs. The resulting quasiparticles diffuse along the superconducting fin, producing a signal when they reach the TES. By determining a correlation between detections in the anti-co and the X-ray detector one can identify and flag these background events. We have fabricated and tested a single-channel prototype anti-co device on a 1.5 $$\times $$ 1.9 cm $$^2$$ chip. We have measured the signals in this device from photons of several energies between 1.5 and 60 keV, as well as laboratory background events, demonstrating a threshold $$\sim $$ 100 times lower than is needed to detect minimum ionizing particles. [ABSTRACT FROM AUTHOR]

The Soft X-ray Spectrometer (SXS) instrument (Mitsuda et al., 2010) [1] on Astro-H (Takahashi et al., 2010) [2] will use a 3-stage ADR (Shirron et al., 2012) to cool the microcalorimeter array to 50 mK. In the primary operating mode, two stages of the ADR cool the detectors using superfluid helium at ⩽1.20 K as the heat sink (Fujimoto et al., 2010). In the secondary mode, which is activated when the liquid helium is depleted, the ADR uses a 4.5 K Joule–Thomson cooler as its heat sink. In this mode, all three stages operate together to continuously cool the (empty) helium tank and single-shot cool the detectors. The flight instrument – dewar, ADR, detectors and electronics – were integrated in 2014 and have since undergone extensive performance testing. This paper presents a thermodynamic analysis of the ADR’s operation, including cooling capacity, heat rejection to the heat sinks, and various measures of efficiency. [ABSTRACT FROM AUTHOR]

We present modeling of distributed $$\lambda $$ /4 microwave kinetic inductance detectors (MKIDs) showing how electromagnetic cross coupling between the MKID resonators can occur at frequencies corresponding to the microwave readout signal ( $$\sim $$ 4-8 GHz). We then show system beam pattern measurements in the reimaged focal plane of a 72 detector array of lens-antenna coupled MKIDs at 850 GHz, which enables a direct measure of any residual optical crosstalk. With use of transmission line bridges we see no residual cross coupling between MKIDs and hence low crosstalk down to the $$-$$ 30 dB level, with near Gaussian shape (limited by reimaging optics) to $$-$$ 10 dB level. [ABSTRACT FROM AUTHOR]

Calorimetric low temperature detectors (CLTD's) have been included in a B-ToF setup, that has already been used several times to perform energy loss measurements at the accelerator laboratory of the University of Jyväskylä. The new experimental setup enabled a precise determination of stopping power data for 0.05-1 MeV/u $$^{131}$$ Xe ions in carbon, nickel and gold. The results are presented and compared to data from literature and theoretical predictions. As a by-product, due to the excellent energy resolution of CLTD's for heavy ions at low energies, an observation of channeling effects in very thin polycrystalline targets and a determination of the channeling energy loss for 0.1-0.5 MeV/u $$^{131}$$ Xe-ions in Ni- and Au-absorbers was possible. [ABSTRACT FROM AUTHOR]

Recent years have witnessed many exciting breakthroughs in neutrino physics. The detection of neutrino oscillations has proved that neutrinos are massive particles but the assessment of their absolute mass scale is still an outstanding challenge in today particle physics and cosmology. Due to their abundance as big-bang relics, massive neutrinos strongly affect the large-scale structure and dynamics of the universe. In addition, the knowledge of the scale of neutrino masses, together with their hierarchy pattern, is invaluable to clarify the origin of fermion masses beyond the Higgs mechanism. The mass hierarchy is not the only missing piece in the puzzle. Theories of neutrino mass generation call into play Majorana neutrinos and there are experimental observations pointing to the existence of sterile neutrinos in addition to the three ones weakly interacting. Since low temperature detectors were first proposed for neutrino physics experiments in 1984, there have been impressive technical progresses: today this technique offers the high energy resolution and scalability required for leading edges and competitive experiments addressing the still open questions. [ABSTRACT FROM AUTHOR]

We present the first measurements on the proposed magnetically-tuned superconducting transition-edge sensor and compare the modified resistive transition with the theoretical prediction (Sadleir et al., IEEE Trans App Supercond 23:2101405, ). A TES's resistive transition is customarily characterized in terms of the unitless device parameters α and β corresponding to the resistive response to changes in temperature and current respectively. We present a new relationship between measured IV quantities (sensor current I and voltage V) and the parameters α and β and use these relations to confirm we have stably biased a TES with negative β parameter with magnetic tuning. Motivated by access to this new unexplored parameter space, we investigate the conditions for bias stability of a TES taking into account both self and externally applied magnetic fields. [ABSTRACT FROM AUTHOR]

Ionization detectors, based on the drift and collection of charges in high purity Germanium crystals (HP-Ge), are commonly used for gamma and particle detection. In the field of very low temperature detectors, several major experiments, like EDELWEISS or CDMS, are using such devices combined with a simultaneous measurement of the detector heat pulses, to search for dark matter in the universe. The leakage current between the charge collecting electrodes of the detectors must be kept as low as possible to preserve performance in terms of high resolution and low threshold. We present results concerning the surface treatment of EDELWEISS HP-Ge crystals, aiming at the reduction of their leakage currents at temperatures below 4 K. Among the explored solutions, a post-process dry-etching using XeF $$_{2}$$ (xenon difluoride) gives very promising and reproducible results. The modification of the Ge surface by this treatment and its effect on the low temperature leakage currents are discussed. [ABSTRACT FROM AUTHOR]

Abstract: 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 163Ho using MMCs having the radioactive 163Ho ions implanted in the absorber. The isotope 163Ho decays through electron capture to 163Dy and features the smallest known value. This peculiarity makes 163Ho a very interesting candidate to investigate the value of the electron neutrino mass by the analysis of the energy spectrum. The implantation of 163Ho 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. Moreover the performance of the detector prototype having the 163Ho ions implanted in the absorber is already close to the requirements needed for an experiment with sub-eV sensitivity to the electron neutrino mass. Based on these results, an optimized detector design for future 163Ho experiments is presented. [Copyright &y& Elsevier]

We discuss the current design of the cold hardware and cold electronics to be used in the upcoming SuperCDMS Soudan deployment. Engineering challenges associated with such concerns as thermal isolation, microphonics, radiopurity, and power dissipation are discussed, along with identifying the design changes necessary for SuperCDMS SNOLAB. The Cryogenic Dark Matter Search (CDMS) employs ultrapure 1-inch thick, 3-inch diameter germanium crystals operating below 50 mK in a dilution cryostat. These detectors give an ionization and phonon signal, which gives us rejection capabilities regarding background events versus dark matter signals. [ABSTRACT FROM AUTHOR]

Precise measurements of the cosmic microwave background (CMB) is crucial to cosmology, since any proposed model of the Universe must account for the features of this radiation. E_cient very large bolometer arrays (>10,000 pixels) constitute an important challenge for CMB observations and are actually developed by many groups worldwide. We present here an explorative new bolometer design based on a structure that simplifies the fabrication process and exhibits high sensitivity. This innovative device replaces delicate membrane-based structures and eliminates the mediation of phonons: the incoming energy is directly captured and measured in the electron bath of an appropriate sensor and the thermal decoupling is achieved via the intrinsic electron-phonon decoupling of the sensor at very low temperature. Reported results come from a 204-pixel matrix of NbSi transition edge sensors with a meander structure fabricated on a 2-inch silicon wafer using electron-beam co-evaporation and standard lithography process. To validate the application to CMB measurements, we have realized an optical calibration of our sample in the focal plane of a dilution cryostat test bench. [ABSTRACT FROM AUTHOR]

The CRESST Dark Matter Search aims to detect Dark Matter particles via their elastic scattering off nuclei in scintillating target crystals. A simultaneous measurement of a phonon and light signal allows to efficiently discriminate the dominant beta and gamma background from expected nuclear recoil signals. For a given light detector and reflector, it is the scintillation efficiency of the crystal which determines the lowest energy for which the active background discrimination is still efficient. Crystals with a higher light output therefore can improve the overall sensitivity of the experiment. In this context, measurements of the light yield of CsI (undoped) and CdWO crystals at milli-Kelvin temperature are presented. Furthermore we report on first results of measurements of these crystals in conventional CRESST configuration. [ABSTRACT FROM AUTHOR]

The TES cryogenic detectors, due to their high spectral resolution and imaging capability in the soft X-ray domain, are the reference devices for the next proposed space missions whose aims are to characterize the spectra of faint or diffuse sources. ATHENA is the re-scoped IXO mission, and one of its focal plane instrument is the X-ray Microcalorimeter Spectrometer (XMS) working in the energy range 0.3-10 keV. XMS will be able to achieve the proposed scientific goals if a background lower than 0.02 cts/cm/s/keV is guaranteed. The studies performed by GEANT4 simulations depict a scenario where it is mandatory to use an active Anti-Coincidence (AC) to reduce the expected background in the L2 orbit down to the required level. This is possible using a cryogenic AC detector able to provide a rejection efficiency of about 99%. We are developing for this purpose a TES-based detector made by Silicon absorbers (total assembled area about 1 cm and 300 μm thick) and sensed by a Ir:Au TES. All the work done for IXO is applicable to ATHENA, with more margins due to the smaller area required for the detector. Here we present the results obtained from different samples, as a step towards the final detector design. [ABSTRACT FROM AUTHOR]

We are developing an instrument based on Kinetic Inductance Detectors (KID) known as the Néel IRAM KID Array (NIKA). Leveraging the experience gained from the first generation NIKA in 2009, an improved, dual-band (150 GHz and 240 GHz) instrument has been designed and tested at the Institut of RadioAstronomie Millimetrique (IRAM) 30-meter telescope in October 2010. The performances, in terms of sensitivity on-the-sky at 150 GHz, are already comparable to existing state-of-the-art bolometer-based instruments. NIKA represents thus the first real proof that KID are a viable technology for ground-based Astronomy. We will describe the instrument, the most recent results and the future plans for building a large resident mm-wave camera. [ABSTRACT FROM AUTHOR]

Absorbers play an important role in all radiation detectors, providing effective energy absorption, fast relaxation and spatial expansion of the excitation volume. A review of the details of energy down-conversion in metal absorbers, both normal metals and superconductors, is given. We discuss the initial absorption of a quantum of energy and ejection of a single photoelectron, followed by fast energy down-conversion via the electron-electron and electron-phonon interactions. We describe the spatial and spectral evolution of the distributions of electronic excitations and phonons, together with the mean energy loss and fluctuations. We also review some recent results regarding thermalization in superconductors at low temperatures, a poorly understood area but one which is crucial for many low temperature devices. [ABSTRACT FROM AUTHOR]

We have developed a coplanar waveguide (CPW) Kinetic Inductance Detector consisting of Al and NbTiN, coupled at its shorted end to a planar antenna. To suppress the odd mode due to direct coupling to sky radiation by the KID we have also developed freestanding metal air bridges. [ABSTRACT FROM AUTHOR]

A high light yield at low temperatures is one of the key criteria in the choice of scintillating target crystals for the CRESST-II Dark Matter search. We perform a feasibility study on ZnWO4 crystals as scintillating targets for the CRESST-II experiment. The light yield and the quenching factors of ZnWO4 at mK temperatures are given for the first time. [ABSTRACT FROM AUTHOR]

A multi-pixel TES array is one of the attractive methods to read-out the incident x-ray position, which simplifies a read-out circuit for imaging applications. We fabricated a ten-pixel Ir/Au TES microcalorimeter with asymmetrical slits parallel to the electric current, and analyzed its noise and signal characteristics. The device was successfully operated in a strong electro-thermal feedback (ETF) mode. However, very large excess noise is observed, which cannot be explained by the noise theory for a single pixel TES. We have modeled the multi-pixel TES array as separated thermal group components, and analyzed noise performance theoretically. As a result, the current noise in our theory is well agreed with the measured noise at a low frequency below 3 kHz. From the x-ray irradiation measurements, ten divided signal groups are observed, which will be associated with the incident x-ray position pixel. The best energy resolution was 18 eV (FWHM) for 5.9 keV x-rays at 0.5 μV bias voltage. [ABSTRACT FROM AUTHOR]

Abstract: We present first significant limits on WIMP dark matter by the phonon-light technique, where combined phonon and light signals from a scintillating cryogenic detector are used. Data from early 2004 with two 300g CRESST-II prototype detector modules are presented, with a net exposure of 20.5kg days. The modules consist of a CaWO4 scintillating “target” crystal and a smaller cryogenic light detector. The combination of phonon and light signals leads to a strong suppression of non-nuclear recoil backgrounds. Using this information to define an acceptance region for nuclear recoils we have 16 events from the two modules, corresponding to a rate for nuclear recoils between 12 and 40keV of (0.87±0.22) events/(kgday). This is compatible with the rate expected from neutron background, and most of these events lie in the region of the phonon-light plane anticipated for neutron-induced recoils. A particularly strong limit for WIMPs with coherent scattering results from selecting a region of the phonon-light plane corresponding to tungsten recoils, where the best module shows zero events. [Copyright &y& Elsevier]

An adiabatic demagnetization refrigerator (ADR) is almost the only way to keep detectors operating at low temperatures below 100 mK in the microgravity of space. We have proposed a garnet with a rare-earth element, (ErxY1−x)3Al5O12, as a suitable magnetocaloric material for ADRs, and examined the x dependence of the cooling performance using single crystals. A broad hump appearing in the temperature dependence of the specific heat at zero field shifts toward a higher temperature with increasing x, 339±36 mK for x=0.5, suggesting that the hump structure is caused by magnetic interactions among Er3+ ions. Combining magnetization and specific heat data, we obtained the field and temperature dependences of the magnetic entropy. The estimated mass needed for an ADR salt pill for x=0.5 is 20–25% smaller than that for x=0.3, at an operating temperature of 60 mK. This is due to its high density of the Er3+ magnetic ions. This mass corresponds to about 5.7 kg, when assuming the same conditions as the ADR used for the Astro-E/XRS microcalorimeters. [Copyright &y& Elsevier]