Shortly after X-rays were discovered in 1895, Antoine Henri Becquerel (1852-1908) tried to show the relationship between X-rays and phosphorescence of uranium salts. In one of his experiments a photographic plate wrapped in black paper, placed a sample of uranium salt on it and exposed to sunlight. By revealing the plot appeared that the rays emitted by the salt had penetrated through the paper. Later, Becquerel was preparing to repeat the experiment, but as the sunlight was intermittent, placed in a drawer assembly. Days later revealed the plate, expecting to find only weakly affected. He was astonished to see a strong image on the plate. He repeated the experiment in total darkness and got the same results, proving that the uranium salt emitted rays affecting the photographic emulsion, without being exposed to sunlight.
Thus it was that Becquerel discovered radioactivity. Marie Curie, two years later, in 1898, gave this phenomenon the name of radioactivity. Radioactivity is the spontaneous emission of particles or rays from the nucleus of an atom. The elements that have this property are called radioactive. Subsequently, Becquerel showed that rays from the uranium could ionize the air and were also able to penetrate through thin
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He found two types of rays, which he called alpha and beta rays. He soon realized that uranium, by issuing these rays transformed into another element. In 1912 they were already known more than 30 radioactive isotopes and today more known. Paul Villard discovered gamma rays in 1900, a third type of rays emitted by radioactive material that is similar to X-rays According to the description of the nuclear atom, Rutherford the phenomenon of radioactivity was attributed to reactions that take place in the nuclei of atoms. Transmutation or transformation of the elements is the conversion of a chemical element in another, by natural or artificial