24.1 Alpha-particle scattering experiment

• A narrow beam of alpha particles, all of the same Ek and radioactive source, are targeted at a thin piece of gold foil. The particles are then deflected on a zinc sulfide screen.
• The scattering experiment led to the following of two observations, both which didn't support Thomson's plum pudding model of the atom; passing of alpha particles and deflection.
• Passing of alpha particles- Most of the alpha particles passed straight through the thin gold foil with very little scattering, about 1 in every 2000 alpha particles.
• Deflection of alpha particles- Very few of the alpha particles about one in every 10000 were deflected through angles of more than 90 degrees.
• The passing of the alpha particles suggested that most of the atom was empty space with most of the mass concentrated in a small region- the nucleus.
• The deflection of alpha particles concluded that the nucleus was positively charged; it repelled the few positive alpha particles.
• The scattering of the alpha particles from the gold nuclei can be modelled using Coulomb's law, with the alpha particle having a charge of 2e and the gold nucleus having a charge of e.
• Alpha particles that made a head on collision, rebound at a scattering angle of 180 degrees. Some alpha particles collide and create an oblique collision and scattered through an angle of theta.
• Initial kinetic energy of alpha particle = electrical potential energy at distance d;
• Only a few particles are deflected at large angles due to the chance of getting close to the tiny nuclei of atoms is very small.
• Atoms are approximately 10^-10, and nucleus are 10^-15