Discovery of Gamma Rays
Villard investigated the radiation from radium salts that escaped from a narrow aperture in a shielded container onto a photographic plate, through a thin layer of lead that was known to stop alpha rays. He was able to show that the remaining radiation consisted of a second and third type of rays. One of those was deflected by a magnetic field (as were the familiar "canal rays") and could be identified with Rutherford's beta rays. The last type was a very penetrating kind of radiation which had not been identified before...
Villard was a modest man and he didn't suggest a specific name for the type of radiation he had discovered. In 1903, it was Ernest Rutherford who proposed to call Villard's rays gamma rays because they were far more penetrating than the alpha rays and beta rays which he himself had already differentiated and named (in 1899) on the basis of their respective penetrating powers. The name stuck.
Read more about this topic: Paul Ulrich Villard
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