In 1885, Wilhem Rontgen while studying the characteristics of cathode rays accidentally discovered X-rays. He also determined the properties of X-rays and got a Nobel prize in 1901 for this discovery. Later scientists studied the diffraction of X-rays by crystals and Bragg obtained the spectrum of X-ray by making electrons collide with solid substances.
In 1896, Becquerel studied the type of the visible light emitted by different substances when X-rays are incident on them. He also observed that invisible radiations affecting photographic plates were emitted by the atoms of uranium. In 1898, Madam Curie also did similar experiments with some other compounds. Such radiations were named radioactive radiations and the phenomenon was called radioactivity by her.
In 1908, Rutherford measured the number of a-particles emitted by one gram of Radium and their total charge and concluded that the charge of a-particle is twice that of the b-particle.
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