Search

The CRESST experiment in its first phase is using sapphire detectors with tungsten phase transition thermometers to search for dark matter WIMPs. At present Four 262 g detectors are performing first measurements under low background conditions. Detector performance as well as preliminary results from the background runs are presented. A second phase of CRESST using CaWO4 and simultaneous measurement of phonons and scintillation light is in preparation. (C) 2000 Elsevier Science B.V. All rights reserved.

Results of the CRESST experiment at Gran Sasso using 262-g sapphire calorimeters with tungsten phase transition thermometers are presented. Calibration and analysis methods are described. Data taken in 2000 have been used to place limits on WIMP dark matter particles in the Galactic halo. The sapphire defectors are especially sensitive to low-mass WIMPs with spin-dependent interaction and improve on existing limits in this region. (C) 2003 MAIK "Nauka/Interperiodica".

With simultaneous measurement of the temperature signal and the scintillation light of a CaWO4 absorber crystal, it is possible to reject the gamma and electron background in the Cryogenic Rare Event Search with Superconducting Thermometers experiment. In order to understand the different events from various particles correctly a neutron calibration experiment and other tests are necessary. Using an existing accelerator facility these tests will be performed above ground. For such an experiment, a detector with good stability at high count rates is necessary. The detectors used in the Gran Sasso Laboratory are equipped with W-thermometers. They show long decay times and need active stabilisation and therefore are not well suitable for experiments with high count rates. We report on developments and first results on detectors based on Ir/Au-thermometers in electrothermal feedback mode.

Using the proximity effect of iridium and gold we fabricate sensitive phase transition thermometers. In spite of problems with other material combinations iridium/gold thermometers show an excellent long-term stability. Up to now we reached transition temperatures in the range from 20 to 100 mK on different absorber materials for example silicon, germanium and sapphire. A study of detectors consisting of a dielectric sapphire absorber, an Ir/Au thermometer and an additional superconducting film is presented. In this case some phonons produced by an interaction in the absorber can break up Cooper–Pairs in the superconducting film. Some energy is stored in the quasiparticle system and reemitted into the absorber with a delay. The recombination phonons are again detected with the thermometer. From the pulse shape of the temperature signal the lifetime of the quasiparticles can be extracted. The results for aluminum and tantalum are presented.

The energy resolution of aluminum superconducting tunnel junctions (Al-STJs) has been improved by the introduction of a metallic buffer layer underneath the junction. When irradiated by 5.9 keV X-rays, a resolution of 12 eV (FWHM) was achieved for a junction size of 100×100 μm 2 . A mobile refrigerator system allowed to characterize these devices at the PTB-beamlines of the electron storage rings Bessy I and Bessy II. They showed linear energy response in the range between 200 eV and 6.5 keV and a strong increase in reduced energy events if irradiated at X-ray energies below the Al absorption edge at 1.56 keV.

An improvement of the statistical and systematic uncertainty beyond the level achieved in GALLEX is an essential prerequisite for GNO. As major contributions to these errors are associated with the detection of the EC-decay of 71 Ge in miniaturized gas counters, low-temperature calorimetric detectors (LTCs) might provide a promising alternative for a later phase of GNO. We report the status of our R&D project on optimization of LTCs for this application.

We are developing cryogenic detectors based on Ir/Au phase transition thermometers and superconducting aluminium tunnel junctions for different applications, where a high-energy resolution and a low detection threshold is required. These applications comprise low background experiments such as CRESST and GNO as well as high-energy resolution X-ray spectroscopy for astrophysics and fluorescence analysis where energy resolutions below 30 eV (FWHM) at 5.89 keV were achieved.

Cryogenic detectors based on iridium-gold phase transition thermometers are being developed for various applications in astroparticle physics, aiming at high energy resolution, low energy threshold and moderate count rates. A microcalorimeter with an energy resolution of 15.5 eV (FWHM) for the 55 Mn Kα 1 x-ray line for tentative use in an analytical x-ray system (e.g. SEM, TRFA) is presented.

An improvement of the statistical and systematic uncertainty beyond the level achieved in GALLEX is an essential prerequisite for GNO. As major contributions to these errors are associated with the detection of the EC-decay of 71 Ge in miniaturized gas counters, low temperature calorimetric detectors might provide a promising alternative for a later phase of GNO. We report first results achieved in measurements of the EC-decaying isotopes 71 Ge and 37 Ar with cryogenic calorimeters.

Results of the CRESST experiment at Gran Sasso using 262 g sapphire calorimeters with tungsten phase transition thermometers are presented. Calibration and analysis methods are described. Data taken in 2000 have been used to place limits on WIMP dark matter particles in the galactic halo. The sapphire detectors are especially sensitive for low-mass WIMPS with spin-dependent interaction and improve on existing limits in this region.

The neutrino capture reaction 71Ga(νe,e−)71Ge and the reverse EC-decay is used by GNO to monitor the flux of solar neutrinos in a routinely operating neutrino observatory. Low temperature detectors (LTDs) offer a better performance concerning efficiency, energy resolution and threshold than the proportional counters that are used now. We report on measurements with a detector setup with absorption in 4 π and counting efficiency near 100%. Activated germanium has been integrated succesfully in the LTD setup by thermal decomposition of GeH4.

A possibility to search for elementary particles as dark matter candidates is to detect elastic scattering with cryogenic detectors. For the interpretation of the data one has to determine the detector response to nuclear recoils, the so-called quenching factors. They can differ for the heat-, for the scintillation- and for the ionization-signal and can be measured by scattering of neutrons. The CRESST- and the EDELWEISS-collaborations have set up a neutron scattering facility for cryogenic detectors at the tandem-accelerator of the Munich ‘Maier-Leibniz-Labor.’ The scattering angle and the time-of-flight of the neutrons are measured by an array of liquid scintillator cells. The pulsed high energy (11 MeV) neutron beam is created by nuclear reaction of a 11B on a H2-gas target. The set-up and the results of first tests are presented.

A slight deviation from linearity has been detected for single aluminum superconducting tunnel junction (Al-STJ) detectors in the energy range between E=1.74 keV and E=6.49 keV. The nonlinearity can be explained by the escape of recombination phonons into the substrate. Varying the size of the junction shows that the recombination of the quasiparticles takes place after their diffusive propagation across the junction. Pulse shape analysis allows to identify background events that are caused by photo-and Auger-electron propagation. For a detector system based on a Al-STJ with a Pb absorber pulse shape analysis allows to separate events related to absorption in the STJ and in the absorber.

With the simultaneous measurement of the temperature signal of a CaWO4 absorber crystal and the scintillation light, it is possible to reject the gamma and electron background in the search for dark matter particles. We report on an alternative new light detector design for the CRESST experiment. For the light detector we use iridium/gold phase transition thermometers with a special circular structure and an Al phonon collector on a silicon substrate. With this detector an energy threshold of 22.3 eV on a 5 σ level was achieved. The light detector was tested in coincidence with a phonon measurement of a 300 g CaWO4 crystal. The phonons from the CaWO4 crystal were measured with an Ir/Au thermometer with a transition temperature of 32 mK.

Results of the CRESST experiment at Gran Sasso using 262 g sapphire calorimeters with tungsten phase transition thermometers are presented. Calibration and analysis methods are described. Data taken in 2000 have been used to place limits on WIMP dark matter particles in the galactic halo. The sapphire detectors are especially sensitive for low-mass WIMPS with spin-dependent interaction and improve on existing limits in this region.

Data taken by CRESST with a cryogenic detector system based on 262 g sapphire crystals has been used to place limits on WIMP dark matter in the Galactic Halo. The experiment was especially sensitive for low-mass WIMPs with spin-dependent cross sections and improves on existing limits in this region. © 2002 Elsevier Science B.V. All rights reserved.

The CRESST experiment seeks hypothetical WIMP particles that could account for the bulk of dark matter in the Universe. The detectors are cryogenic calorimeters in which WIMPs would scatter elastically on nuclei, releasing phonons. The first phase of the experiment has successfully deployed several 262 g sapphire devices in the Gran Sasso underground laboratories. A main source of background has been identified as microscopic mechanical fracturing of the crystals, and has been eliminated, improving the background rate by up to three orders of magnitude at low energies, leaving a rate close to one count per day per kg and per keV above 10 keV recoil energy. This background now appears to be dominated by radioactivity, and future CRESST scintillating calorimeters which simultaneously measure light and phonons will allow rejection of a great part of it., To appear in the proceedings of the CAPP2000 Conference, Verbier, Switzerland, July, 2000 (eds J. Garcia-Bellido, R. Durrer, and M. Shaposhnikov)

We present the current status of CRESST (Cryogenic Rare Event Search using Superconducting Thermometers) project and new results concerning detector development. The basic technique involved is to search for WIMPs by the measurement of non-thermal phonons, as created by WIMP-induced nuclear recoils. Combined with our newly developed method for the simultaneous measurement of scintillation light, strong background discrimination is possible, resulting in a substantial increase in WIMP detection sensitivity.

We are developing both superconducting tunnel junctions and phase transition thermometers for high resolution x-ray spectroscopy. A resolution of 12 eV has been achieved for aluminum tunnel junctions when irradiated by 5.9 keV x-rays. These devices show linear energy response in the range between 200 eV and 6.5 keV. Phase transition thermometers consisting of an iridium/gold bi-layer and a gold absorber gave a resolution of 15.5 eV at 5.9 keV. The application of both sensor types is facilitated considerably by the use of an ADR cryostat. This mobile system allowed to characterize tunnel junctions at the Bessy I synchrotron.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have been developing cryogenic detectors for astro-particle physics applications including search for Dark Matter, neutrino physics and X-ray astronomy. Most recently we started the development of high resolution X-ray detectors based on superconducting tunnel junctions (STJs) and superconducting phase transition thermometers (SPTTs) / transition edge sensors (TES) for microanalysis applications. Both types of sensors are being investigated as well as the cryogenic setup for applications on a scanning electron microscope (SEM).

The CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) experiment at the Gran Sasso Laboratory will search for dark matter WIMPs using cryogenic detectors. In the first stage we will use four 262 g sapphire crystals with thresholds of about 0.5 keV. This low threshold gives us sensitivity to WIMP masses below 10 GeV, making CRESST complementary to other dark matter searches. The main installation in Gran Sasso is now complete and we report on the first detector tests.

Cryogenic detectors with excellent energy resolution and low energy threshold far beyond the level of semiconducting detectors open a variety of new. applications in physics including search for Dark Matter in the universe [2], neutrino physics [3], and IR-, UV- and X-ray astrophysics [4, 9]. Interdisciplinary fields where cryogenic detectors have already shown promising results are the detection of biomolecules [5] and X-ray spectroscopy at synchrotron beam lines [6] and in scanning electron microscopes (SEMs) [7]. For both, astrophysical and analytical use, the development of high resolution microcalorimeters based on iridium/gold phase transition thermometers and aluminum tunnel junctions for use in a compact and universal detector system was initiated.Our cryogenic microcalorimeters consist of an absorber, a temperature sensor and a weak coupling to a heat sink. An X-ray photon interacts with the absorber and raises its temperature. The sensor measures the temperature increase and the system then, mediated by the coupling, relaxes back to its operating temperature.

Future radiochemical solar neutrino experiments as G no or the proposed Li-experiment require an efficient detection of the back-decay of the neutrino induced radioactive atoms with good energy resolution and low threshold. Cryogenic detectors offer a better performance concerning efficiency, resolution and threshold than the proportional counters that are used now. We discuss motivation and first measurements.

TO evaluate the effect of salinity increases in crop yields and soil salination, water was artifically salinated and applied by sprinkler irrigation to crops on a clay and a sandy clay loam. Water with a level of total dissolved solids (TDS) raised to 1,350 mg/L TDS pro-duced significantly lower yields of snap beans, carrots, and onions than did Colorado River water of 875 mg/L TDS. The reductions were about as predicted by current salt-tolerance rankings. The driest irrigation treatment (a ratio of irrigation to pan evaporation of 0.57) gave a significant reduction in alfalfa yield after two years. Dur-ing the two years, salts accumulated faster than applied in the irrigation water, indicating upward movement from the 1.8-m water table. The intermediate irrigation (ratio 0.67) gave a similar increase in soil salinity but no significant yield reduction in alfalfa after 32 months. The wettest irrigation (ratio 0.78) gave the highest yields and less salt accumulation than was applied, indicating par-tial leaching.