radioactivity _ _ _ Discovering alpha particles completely through paper , beta particles through aluminum plates and gamma rays through partial resistance Stir. He observed that the nucleus of a uranium metal emits spontaneous special piercing rays or radiation spontaneously. The beam is named after him. He noticed that the ray emitted from the element continued to emit until it was transformed into a completely new element. Later, Madame Curie and her husband Pierre Curie conducted extensive research and found that the nuclei of heavy elements such as radium , polonium , thorium , actinium, etc., emit the same type of radiation as bacillus , now known as radioactive rays. The elements from which radioactive rays are emitted are called radioactive elements. This phenomenon of emission of radioactive rays is called radioactivity .