The previous setup was unsuitable for doing this because the tube contained several radioactive substances radium plus its decay products and thus the alpha particles emitted had varying rangesand because it was difficult for them to ascertain at what rate the tube was emitting alpha particles. The astronomer Arthur Eddington called Rutherford's discovery the most important scientific achievement since Democritus proposed the atom ages earlier. The column was also a tube by which air was pumped out of the cylinder. Using the same apparatus again, they slowed the alpha particles by placing extra sheets of mica in front of the alpha particle source. Geiger and Marsden didn't know what the positive charge of the nucleus of their metals were they had only just discovered the nucleus existed at allbut they assumed it was proportional to the atomic weight, so they tested whether the scattering was proportional to the atomic weight squared. The disc could be rotated by means of a rod P to bring each window in front of the alpha particle source R.
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Main articles: Rutherford model and Rutherford-Bohr model.
Namespaces Article Talk. At one end of the tube was a quantity of " radium emanation " R that served as a source of alpha particles. Inhe received a visit from a German physicist named Hans Geigerand was so impressed that he asked Geiger to stay and help him with his research.
The microscope which he used to count the scintillations on the screen was affixed to a vertical millimeter scale with a vernier, which allowed Geiger to precisely measure where the flashes of light appeared on the screen and thus calculate the particles' angles of deflection.
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|Rutherford thus rejected Thomson's model of the atom, and instead proposed a model where the atom consisted of mostly empty space, with all of its positive charge concentrated in its center in a very tiny volume, surrounded by a cloud of electrons.
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A microscope M was used to count the scintillations on the screen and measure their spread. The rotating disc in the center had six holes which could be covered with foil.
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Alpha particles are tiny, positively charged particles that are spontaneously emitted by certain substances such as uranium and radium.
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The Geiger–Marsden experiments were a landmark series of experiments by which scientists Thomson was the scientist who discovered the electron, and that it was a component of every atom.
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Geiger and Marsden covered the holes of the disc with foils of gold, tin, silver, copper, and aluminum. Alpha particles are too tiny to be seen with a microscope, but Rutherford knew that alpha particles ionize air molecules, and if the air is within an electric field, the ions will produce an electric current.
Rutherford asked Geiger to investigate just how much matter could scatter alpha rays.
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He constructed an airtight glass tube from which the air was pumped out. They spotted alpha particles bouncing off the metal foil in all directions, some right back at the source. This model was devised by Lord Kelvin and further developed by J.
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|Back Matter Pages Geiger then pumped out the air and placed some gold foil over the slit at AA.
The above calculation is but an approximation of what happens when an alpha particle comes near a Thomson atom, but it is clear that the deflection at most will be in the order of a small fraction of a degree. The popular theory of atomic structure at the time of Rutherford's experiment was the " plum pudding model ". The existence of protons and neutrons was unknown at this time.