Rutherford's Experiment Part II
Earnest Rutherford had been studying alpha particles, which he discovered since 1898. In 1909 he was confronted with some rather weird alpha-particle behavior that he had to explain.Hans Geiger and Ernest Marsden aimed a stream of alpha particles at a thin gold foil for several months in 1909. Geiger cites a thickness of 8.6 x 10 to the -6 power for the foil. In fact, the foil had to be supported on a glass plate due to its thinness. There were three major findings in this experiment:
1. Almost all of the alpha particles went thorough the gold foil as if it were not even there. Those alpha particles continued on a straight-line path until they hit the detector screen.
2. Some of these particles were deflected only slightly, usually 2 degrees or less. Geiger found that an alpha particle was deflected about 1/200th of a degree, on average, by each single encounter with a gold atom. The most probable angle of deflection for one gold foil turned out to be about 1 degree.
3. A very few alpha particles were turned through an angle of 90 degrees or more.
His solution to the enigma of explaining both large and small angle scattering was the nucleus. It was already well documented that the atom had a radius of about 10 to the -8 power cms. The Thomson model of the atom spread the entire mass of the atom throughout that space. What Rutherford did was put most of the mass of the atom at the center of the atom, in a space much smaller than that of the atom itself.
Rutherford never used the word "nucleus" in his paper. He called this the "charge concentration." In 1912, in a book he published, he devotes a few pages the word nucleus once.
After all of this, Rutherford closed the door on the basic structure of the atom. No serious challenge has been made to his word since to the legitimacy of his model of the atom.