OPTIMIZATION OF THE CZOCHRALSKI GROWTH PROCESS FOR CALCIUM TUNGSTATE DETECTOR CRYSTALS

CRESST is an experiment for the direct detection of (lark matter (WIMPs) via nuclear recoil measurement. The expected very low event rates and the low energy transfer in the keV range demand low background rates and extremely sensitive detectors. Thus the need for detector crystals with good optical and phonon properties combined with high radioactive purity arises. To achieve these goals, the control over the raw materials and their processing, in particular the crystal growth, is important. A new Czochralski furnace has been installed at the crystal laboratory of the Physik-Department in Garching to meet the delicate conditions required to grow CaWO4 crystals of sufficient size.