Hans Kraus

Abstract:

The importance of luminescent tungstates and molybdates in several technological applications motivated the study of the structural, luminescence and scintillation properties of the MgWO4-MgMoO4 system. X-ray diffraction studies allowed the identification of three main types of structures in the pseudo-binary MgWO4-MgMoO4 system (sanmartinite β-MgMoO4, cuprosheelite α-MgMoO4, and wolframite MgWO4) and the refinement of the parameters of the crystal lattice. It is found that the single-phase solid solution MgMo 1-xWxO4 with a β-MgMoO4 structure is created only at x<0.10, while for a higher tungsten content a mixture of different phases is formed. The x-ray luminescence spectra of a series of samples of the MgWO4-MgMoO4 system are measured at T = 8 K. The principal emission bands are assigned to the main structural phases as follows: β-MgMoO4, 520 nm; α-MgMoO4, 590 nm; MgWO4 (wolframite), 480 nm. The phase composition of the sample determines the actual shape of the observed spectra. Possible relations between the crystal structure and luminescence properties of different phases are discussed in terms of a configuration coordinate model. Of all the compounds under test, MgWO4 is found to have the best scintillation response for particle excitation (0.90 0.15 that of ZnWO4 at T = 295 K). Further, the light yield also remains high with decreasing temperature, which makes this material potentially useful for cryogenic applications. © 2008 IOP Publishing Ltd.

Abstract:

We have measured the superconducting transition temperatures of commercial alloys Dural and titanium 6Al-4V, to assess their suitability for use in the cryoEDM neutron electric dipole moment experiment. Our sample of aluminium alloy Dural became a superconductor at 0.84 0.07K but the titanium alloy did not show any superconducting behaviour down to the experimental limit of 0.17 0.11K. © IOP Publishing Ltd.

Abstract:

European Underground Rare Event Calorimeter Array (EURECA) will be an astro-particle physics facility in the Laboratoire Souterrain de Modane, aiming to directly detect galactic dark matter. The EURECA collaboration unites CRESST, EDELWEISS and the Spanish-French experiment ROSEBUD, thus concentrating and focussing effort on cryogenic detector research in Europe into a single facility. The aim is to explore WIMP - nucleon scalar cross sections in the 10-9 - 10-10 picobarn region with a target mass of up to one ton. A major advantage of EURECA is the planned use of more than just one target material (multi target experiment for WIMP identification).

Abstract:

CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) is a low temperature experiment dedicated to the direct dark matter detection via nuclear recoil. It is located in Hall A of the Laboratori Nazionali del Gran Sasso, Italy. Scintillating CaWO4 crystals operated at a few mK are utilized as target forWIMPs (Weakly Interacting Massive Particles), which are expected to scatter predominantly on the heavy tungsten nuclei. As for background rejection, CRESST uses the phonon-light technique, where two different quantities of an interaction are recorded: the heat production in the CaWO4crystal and the simultaneous emission of scintillation light, which is monitored by a second low-temperature detector, the light detector. The information provided by both detectors allows a powerful background discrimination on an event by event basis. After a major upgrade phase, CRESST-II has now successfully completed a commissioning run during 2007, the results of which are presented in this article.