Nuclear and particle physics

The nuclear atom, particle accelerators and detectors, mass-energy, and the standard quark-lepton model.

Understand what is meant by nucleon number (mass number) and proton number (atomic number)

Understand how large-angle alpha particle scattering gives evidence for a nuclear model of the atom and how our understanding of atomic structure has changed over time

Understand that electrons are released in the process of thermionic emission and how they can be accelerated by electric and magnetic fields

Understand the role of electric and magnetic fields in particle accelerators (linac and cyclotron) and detectors (general principles of ionisation and deflection only)

Be able to derive and use the equation $r = \frac{p}{BQ}$ for a charged particle in a magnetic field

Be able to apply conservation of charge, energy and momentum to interactions between particles and interpret particle tracks

Understand why high energies are required to investigate the structure of nucleons

Be able to use the equation $\Delta E = c^2\Delta m$ in situations involving the creation and annihilation of matter and antimatter particles

Be able to use MeV and GeV (energy) and MeV/ $c^2$ , GeV/ $c^2$ (mass) and convert between these and SI units

Understand situations in which the relativistic increase in particle lifetime is significant (use of relativistic equations not required)

Know that in the standard quark-lepton model particles can be classified as baryons (made from three quarks), mesons (a quark and an antiquark), leptons (fundamental particles) and photons, and that the symmetry of the model predicted the top quark

Know that every particle has a corresponding antiparticle and be able to use the properties of a particle to deduce the properties of its antiparticle and vice versa

Understand how to use laws of conservation of charge, baryon number and lepton number to determine whether a particle interaction is possible

Be able to write and interpret particle equations given the relevant particle symbols

An electron and a positron, both effectively at rest, annihilate to produce two identical gamma-ray photons.

(a) Explain why two photons, rather than one, are produced.

(b) Calculate the wavelength of each photon.

Initial momentum is zero, so two photons moving in opposite directions are needed to conserve momentum (1)
Energy of each photon = rest energy of one electron: $E = mc^2 = 9.11 \times 10^{-31} \times (3.00 \times 10^{8})^2$ (1)
$E = 8.2 \times 10^{-14}\,\text{J}$ (1)
$\lambda = hc/E = 2.4 \times 10^{-12}\,\text{m}$ (1)

In Rutherford's alpha-particle scattering experiment, alpha particles were fired at a thin gold foil.

State three observations and the conclusion drawn about the atom from each.

Most alpha particles passed straight through, so most of the atom is empty space (1)
Some were deflected through small angles, so the nucleus is charged (positive, repelling the alpha particles) (1)
A very small number were deflected through more than $90^\circ$ , so most of the mass is concentrated in a very small nucleus (1)

Specification points

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Sample questions