Hans Kraus

Abstract:

We have developed multichannel SQUID systems for two particle physics experiments: a 66-channel system for detector readout in the CRESST dark matter search, and a 12-channel magnetometry system for the CryoEDM neutron electric dipole moment experiment. These different applications have different requirements, for example in the CRESST system it is important to minimise crosstalk, while the CryoEDM system must be shielded from magnetic noise. Future experiments such as the EURECA dark matter project may require systems with a much higher number of channels. (c) 2006 Elsevier B.V. All rights reserved.

Abstract:

CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) employs cryogenic detectors for the direct search for weakly interacting massive dark matter particles (WIMPs). In the second phase of the experiment scintillating calcium tungstate crystals are used to discriminate background by means of different light yield for background and WIMP signals. After first results with this novel technique have been obtained, the experimental setup is being upgraded for further background reduction and larger target mass. The results and present status of the experiment will be presented. © 2006 IOP Publishing Ltd.

Abstract:

Inorganic scintillators are important elements of a new type of cryogenic phonon scintillation detector (CPSD) being developed for single particle detection. These detectors, exhibiting superior energy resolution and the ability to identify the type of interaction in an event, are considered to be the next generation of instrumentation in the search for extremely rare events. This paper presents the latest results of our research on cryogenic scintillators for CPSD applications in the search for dark matter. The paper gives a description of the concept of direct dark matter detection and the operation principles of CPSD, discusses the major material requirements and summarizes the results of investigations over a wide temperature range of the luminescence and scintillation properties of tungstates (CaWO4 and ZnWO4), molybdates (CaMoO4, MgMoO4 and CdMoO4) and Ti-doped Al2O3. © 2006 IOP Publishing Ltd.

Abstract:

The structure of calcium molybdate was studied by means of synchrotron based high-resolution powder diffraction methods in the temperature range 12-300 K. The scheelite structure type was confirmed for CaMo O4 in the temperature region investigated and no structural anomalies were observed. Thermal expansion coefficients extracted from the thermal dependencies of the cell sizes are found to be in good agreement with the predictions from our lattice dynamics calculations that form the background for microscopic interpretation of the experimental data. From the analyses of experimental results and the calculated thermal expansion coefficients, elastic constants, phonon density of states, heat capacities, entropy, and Grüneisen parameters it is concluded that a quasiharmonic lattice dynamics approach provides a good description of these properties for CaMo O4 at temperatures below 800 K. © 2006 The American Physical Society.

Abstract:

A new method for measurements of the scintillation characteristics of materials has been developed. This method, called multiple photon counting coincidence (MPCC) technique, is based on the recording of a sequence of individual photon pulses resulting from a scintillation event. The distribution of the arrival times of these individual photon pulses provides information about the decay characteristic of the scintillation process and the number of photons recorded per scintillation event is proportional to the scintillation light yield. The ability to reject spurious events through off-line analysis is an important advantage of the MPCC method since it allows cleaning of the data set from pile-up events. It is shown that the MPCC technique is particularly well suited for the analysis of slow scintillation processes in the investigation of temperature-dependant scintillator properties. It is now used extensively by our group for the identification and optimisation of scintillating targets for cryogenic low-background rare event searches, such as Dark Matter and 0-v double beta decay experiments.