![]() ![]() He interpreted this rebound as the "backscatter" of a light nucleus (alpha particle) on the heavy nucleus of a gold atom. Rutherford observed the backward bounce of some alpha particles as projectiles sent on the atoms of a thin gold foil. That was the case! It was in darkness and with the naked eye, that Rutherford, Geiger and Marsden counted the scintillations due to the impacts of alpha particles on a screen of zinc sulphide. Rutherford asked a young assistant Ernest Marsden to see if alpha particles were subjected to a high deflection, and even bounced back, when they went through a thin gold foil. Nevertheless an enigma remains: a few alpha particles were deflected. ![]() The result of their observations confirmed the existence of strong electric fields. With his assistant Hans Geiger, Rutherford developed a method to do so. But he thought he should be able to detect and count deflected alpha particles. Observing that high speed alpha particles were deflected by a thin sheet of mica, Rutherford calculated the electric field inside the mica and deduced that it should have been very powerful. He summarized his observations by saying that at atomic scale " the solid matter is transparent" and noticed that "t he space occupied by one cubic meter of solid platinum is as empty as the space between the stars and the earth". In 1903, Philip Lenard, bombarding atoms with cathode rays had noticed that they passed through the atoms as if they could find almost nothing on their trajectory. Rutherford concluded that the atom contained a heavy heart, with positive electric charge, able to push away the alpha The impacts were observed as scintillations in the dark, under the microscope, on a screen of zinc sulphide. ![]() By bombarding a very thin gold foil with alpha particles, Hans Geiger and Ernest Marsden, both students of Rutherford, observed that a small fraction (1 in 8000) of these particles were deflected at large angle as if it bounced off a heavy obstacle. ![]()
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