Particle Physics

Geiger & Marsden fired alpha particles at gold leaf which had a detector screen behind it. They found that a very small proportion of particles (about 1 in 8000) were deflected through large angles (>90^o) while most passed straight through. This lead to the 'Rutherford model of the atom' where almost all of an atoms mass is concentrated in a tiny portion of the atom containing all of an atom's positive charge.

Deep inelastic scattering experiments showed that protons & neutrons have their own internal structure. They are composed of subatomic particles (quarks) and so can no longer be though of as elementary particles. High energy electrons were used to overcome the electrostatic forces and to provide an electron de Broglie wavelength small enough to reveal these tiny particles (quarks).

Quarks: (up/down/strange/charm/top/bottom) are strongly interacting particles.

Leptons: (eg electrons, neutrinos & their anti-particles) are weakly interacting particles.

• Quarks triplets:
• eg neutron = udd (up/down/down) and Proton = uud (up/up/down)