The Discovery of Radioactivity 1896

ê Radioactivity is the instant disintegration of atomic nuclei by the emission of subatomic particles called alpha, and beta particles, or of electromagnetic rays called x-rays and gamma rays.

4 The phenomenon was discovered in 1896 by the French physicist Antoine Henry Becquerel, when he observed that the element uranium can blacken a photographic plate, although separated from it by glass or black paper. He also observed that the rays that produce the darkening are capable of discharging an electroscope indicating that the rays possess an electric charge.