"An experimental arrangement by Geiger and Marsden used a beam of 5.5 MeV alpha particles (M = mega, or 106, 1,000,000 electron volts) from radon placed in a lead block at a specific distance R from the source radiation. A well-collimated beam of the alpha particles fell on a thin metallic sheet of gold ~ 10-4 meters (0.0001 m) thick.
"Most of the alpha particles went through the foil as if spaces existed. A few collided with the atoms in the gold molecules and scattered at different angles. This came to be known as Rutherford Scattering.
"The scattered alpha particles struck a screen coated with a thin layer of ZnS (Zinc Sulfide), placed in such a way that the alpha particles received on the screen made an angle (theta) with the incident beam.
"Each alpha particle produced a flash of light (scintillation), on the screen, observed with a magnifying glass or microscope. 1/~8,000 alpha particles were scattered through an angle > 90 degrees, i.e. it experienced back scattering.
"Rutherford (Geiger and Marsden's former teacher) suggested the large-angle back-scattering could be explained if we assumed the nuclear model of the atom.
"The previous Thomson model, the so-called plum pudding of evenly distributed positive charge and mass of the atom are distributed uniformly over a sphere of radius ~ 10-8 cm, with electrons embed making the atom charge-neutral."
Above excerpt from "Elementary Modern Physics" by Atam P. Arya
The Society of Physics Students: A Century of Revolution - Celebrating 100 years Since the Discovery of the Atomic Nucleus
NobelPrize.org: Ernest Rutherford
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