Search

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.

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.

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.

We describe the results of the GALLEX solar neutrino experiment after completion of the project. In particular, we summarize the results for GALLEX IV (12 solar runs) and for our 71As - spiking experiments. The integral GALLEX result for all 65 solar runs (GALLEX I–IV) is (78 ± 8) SNU (1σ). This is only slightly more than half of the expected rate. The significance of this deficit is assured. • directly by the results from our two 5Cr neutrino source experiments (at the 10% - level), and • indirectly by means of experiments in which 71Ge is generated within the target solution from beta-decaying 71As (at the percent level). GALLEX at Gran Sasso is now succeeded by Gallium Neutrino Observatory). The GNO status as of October 1998 is reported.

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.

We are developing a dark matter detector for Weakly Interacting Massive Particles (WIMPs) using Series Arrays of Superconducting Tunnel Junctions (SASTJs) to read out phonon signals from absorber crystals. We discuss the factors which have determined the choice of our detector scheme. As an improvement over previously produced SASTJs using a shadow mask technique, a new fabrication process of high-quality Al/Al-oxide/Al junctions and SASTJs is being developed using photolithography to define the structures. The processing and the electrical characterisation of the first devices produced in this way are described

We discuss the design of a cryogenic detector for a WIMP dark matter search based on single crystal absorbers and using Series Arrays of Superconducting Tunnel Junctions (SASTJs). The distribution of recoil vectors of target nuclei from WIMP interactions are affected by the motion of the laboratory through the dark matter halo. The angular distribution of recoil directions is skewed due to the motion of the solar system around the galaxy and is modulated by the diurnal and annual rotation of the earth. We discuss the kinematics of the recoil events and how a directional signal might be identified in our cryogenic detectors using the fast response of SASTJs to the ballistic phonons arising in the absorber from WIMP interactions. We consider how the anisotropy of a dark matter recoil distribution can be used to place statistical limits on its component relative to the isotropic background signal. We also consider how the dark matter limit is altered if only the axis of the nuclear recoil, rather than the full recoil direction is available. We also briefly consider the effect of phonon focusing within single crystal absorbers. Focusing will modulate strongly the signal detected by the SASTJs, on the crystal surface, as the position of the interaction within the crystal varies. A comparison is made between the behaviour of phonons in strongly focusing crystals, such as Nb, Si and LiF, and their near isotropic propagation in BaF2.

We are setting up a dedicated neutron-scattering facility in order to study the response of cryogenic detectors to nuclear recoils in preparation for dark matter searches. The design and status of the facility are presented.

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.