ALPHA SCATTERING EXPERIMENT

Rutherford’s alpha scattering experiment, conducted in 1911, was a critical step in the development of the atomic theory. It involved firing alpha particles (helium nuclei) at a thin gold foil and observing their deflection.

The experiment was carried out in the following steps:

1. Rutherford and his colleagues produced a thin sheet of gold foil that was only a few atoms thick. The gold foil was then mounted on a metal plate in the center of a vacuum chamber.
2. They used a radioactive source containing alpha particles and aimed a beam of alpha particles at the gold foil. The alpha particles were positively charged and high-energy, which meant that they could penetrate the thin gold foil.
3. They placed a fluorescent screen behind the gold foil to detect the deflection of the alpha particles.
4. Rutherford and his colleagues expected the alpha particles to pass straight through the gold foil, with no deflection or scattering, as per the prevailing “plum pudding” model of the atom at the time.
5. However, they observed that some of the alpha particles were deflected at large angles, and a small fraction even bounced back in the direction from which they came. This was a significant discovery, as it suggested that the atom was not a homogeneous mass, as was previously believed, but instead had a central, positively charged nucleus.
6. Rutherford concluded that most of the atom’s mass and positive charge was concentrated in a small region at the center, called the nucleus, which was surrounded by a cloud of negatively charged electrons in a mostly empty space.

This experiment provided strong evidence for the nuclear model of the atom and became a cornerstone of modern atomic theory.