T 7669 (OTTO) Thallium(I) bromide anhydrous, beads, −10 mesh, 99.99% Cas 7789-40-4 - used in blue sensitive photodetectors. T 7669 (OTTO) Thallium(I) bromide anhydrous, beads, −10 mesh, 99.99% Cas 7789-40-4 - used as a real-time x-ray image sensor. Further, it acts as a standard for elemental thallium. In addition to this, it is a compound semiconductor used in room temperature X- and gamma-ray detectors.