Deeper Rutherfordhistory 6 ext b
Ernest Rutherford probed inside the atom using alpha particles and found the nucleus. Later, James Chadwick worked out the properties of one of the particles in the nucleus. The next step was to work out what was inside protons and neutrons.
Quark proposal
Rutherford scattering
Murray Gell-Mann and George Zweig had used the patterns in the hadron family to deduce that they were made up of quarks. Protons and neutrons are made of three quarks with two flavours: up and down. But how could physicists get any direct evidence of their existence? The answer was to use Rutherford’s methods on a smaller scale.
Deep elastic scattering
Einstein, energy and mass
Rutherford had fired alpha particles at gold nuclei. However, alpha particles, which are made of two protons and two neutrons, are bigger than a single proton, so they could not be used to get inside a proton. However, the electron is a tiny particle that can be accelerated up to high speeds. This allows it to pass through protons and neutrons and be deflected by any structure that may be inside them. A number of physicists carried out experiments firing beams of electrons at protons and neutrons. Just as Rutherford had done with alpha particles, they measured the numbers of electrons at each angle of deflection. The results were complicated but suggested that there were indeed three particles inside the proton and neutron and that the charges were +2/3 and –1/3 of the charge on the protons. These matched the charges of the proposed up and down quarks.
The story so far
The quark model of hadrons was verified using deep elastic scattering
This involved firing electrons at protons and neutrons and measuring their deflections
Question H8

a) Which two quarks make up protons and neutrons?

b) What are their charges?

c) Which particles were used to probe inside protons and neutrons to verify the existence of quarks?

The story so far
  • The quark model of hadrons was developed to explain the existence and properties of the hundreds of hadrons
  • Rutherford used alpha particle scattering to determine the structure of the atom