Abstract: Thorium tetrabromide has been found to exhibit fluorescence and radioluminescence with emission of blue light in the range from 3400 to 4800 A with a maximum around 4000 A in response to electromagnetic waves shorter than 3000 A, whether ultraviolet, X or gamma rays and also in response to energetic charged particle radiation, such as alpha rays, beta rays, protons and heavy ions. Because of the radioactive decay of thorium, there is a background autoluminescence. Crystals of thorium tetrabromide are transparent to its luminescence radiation and are particularly suitable for radiation detectors and measurements, frequency converter, standards, radioisotopic microgenerators of electricity, and the like. They are also useable as neutron flux detectors, for thermal and fast neutrons because the component elements of the crystal react with neutrons to respectively produce neutrons activation reactions and fission reactions.