• In the 1960s, scattering experiments were performed (similar to Rutherford’s Gold Foil Experiment) where high energy electrons were beamed at protons.
• These electrons had a very high energy and momentum, and thus very short wavelength ( de Broglie equation : ), which allowed its use to probe within a proton’s structure
• The results of the scattering at SLAC(Stanford Linear Accelerator Center), performed by Friedman, Kendall and Taylor suggested that there were finite particles within protons, and proton was not a fundamental particle.

• Experiments with neutrons also showed that a neutrons had properties which were not expected if Neutron was indeed a chargeless elementary particle.
• This could possibly mean that neutron was composed of more fundamental particles which possessed electrical charge.

           Subatomic particles other than electron , proton and neutron were observed and predicted through multiple experiments and theories since 1930’s.

• In 1933, Carl Anderson while investigating cosmic rays , observed a particle that had the same mass as electron but with a positive charge . He had observed the antiparticle of electron – now known as positron.

Extract from Physics Stage 6 Syllabus © 2017 NSW Education Standards Authority (NESA)