how could an alpha particle strike the phosphor screen on the same side of the foil as the alpha particle source?

Question

koikkara · Answer

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Left: Expected results: alpha particles passing through the plum pudding model of the atom undisturbed. Right: Observed results: a small portion of the particles were deflected, indicating a small, concentrated positive charge.

When Rutherford used nitrogen, a very large number of spots was observed, because nitrogen interacts with alpha particles and the protons produced are highly energetic, penetrating enough to pass the metal foil and strike the phosphor.