Interactive Syllabus Extract for

Section 3.2.1 - Particles and Radiation

Particle section notes link

  Useful background You should be able to: Constituents of the atom

Simple model of the atom - proton, neutron, electron - their charge and mass in SI units and relative units. Specific charge of nuclei and of ions. (Atomic mass
unit is included in the A-level Nuclear physics section).

Proton number Z, nucleon number A, nuclide notation

Meaning of isotopes and the use of isotopic data.

Evidence for existence of the nucleus, qualitative study of Rutherford scattering was covered at GCSE - revise it!

- draw from memory a fully labelled diagram of the atom

- draw from memory a table with relative masses, positions and charges of electron, proton and neutron

- appreciate the size of the atom and its nucleus

- calculate the specific charge of a nucleus or ion Stable and unstable nuclei

The strong nuclear force; its role in keeping the nucleus stable;
short-range attraction to about 3 fm, very-short range repulsion below about 0.5 fm;

Unstable nuclei; alpha and beta decay.
Equations for alpha decay and β- decay including the neutrino


The existence of the neutrino was hypothesised to account for conservation of energy in beta decay.

Recall that the strong force acts between baryons

AT i - Demonstration of the range of alpha particles using a cloud chamber, spark counter or Geiger counter.

MS 0.2 - Use of prefixes for small and large distance measurements Particles, antiparticles and photons Candidates should know that every particle has a corresponding antiparticle.
Comparison of particle and antiparticle masses, charge and rest energy in MeV.
Photon model of electromagnetic radiation, the Planck constant,

Knowledge of annihilation and pair production processes and the respective
energies involved.

The use of E = mc2 is not required in calculations

interactive spreadsheet on the Einstein Equation

Candidates should know that the positron, the antiproton, the antineutron and the antineutrino are the antiparticles of the electron, the proton, the neutron
and the neutrino respectively.

- recall the electromagnetic spectrum in order of energies.

- recall and use the equation

defining the terms and using the correct units

Interactive worksheet- recall the names and symbols of particles and their antiparticles and which group they belong to

- use the conservation laws to say whether a reaction is possible or not

AT i - Detection of gamma radiation.

MS 1.1, 2.2 - Students could determine the frequency and wavelength of the two gamma photons produced when a 'slow' electron and a 'slow' positron annihilate each other. The PET scanner could be used as an application of annihilation. Particle Interactions

Four fundamental interactions: gravity, electromagnetic, weak nuclear, strong nuclear. (The strong nuclear force may be referred to as the strong interaction.)

Concept of exchange particles to explain forces between elementary particles.

Knowledge of the gluon, Z0 and graviton will not be tested.

The electromagnetic force; virtual photons as the exchange particle.
The weak interaction limited to β-, β+ decay, electron capture and electron-proton
collisions; W+ and W- as the exchange particles.
Simple Feynman diagrams to represent the above reactions or interactions in
terms of particles going in and out and exchange particles.

- sketch the given Feynman diagrams for beta decay, positron decay, electron capture, particle collisions

- know that the changes from a proton to a neutron and vice versa occur via the weak interaction (using a boson as an exchange particle)

- use the concept of exchange particles to explain forces between elementary particles
- explain why particles 'appear in pairs'

- understand that a particle and its antiparticle annihilate to release energy in the form of a gamma ray

PS 1.2 - Momentum transfer of a heavy ball thrown from one person to another Classification of particles

To know that hadrons are subject to the strong interaction.

Classification of Hadrons:

- baryons (proton, neutron), antibaryons (antiproton and antineutron) and

- mesons (pion, kaon)

Baryon number as a quantum number.

Conservation of baryon number.

Candidates should know that the proton is the only stable baryon into which other baryons eventually decay; in particular the decay of the neutron should be known.

The pion as the exchange particle of the strong nuclear force.

The kaon as a particle that can decay into pions.

Leptons are subject to the weak interaction

Leptons: electron, muon, neutrino (electron and muon types only) and their antiparticles.

Lepton number as a quantum number; conservation of lepton number for muon leptons and for electron leptons.

The muon as a particle that decays into an electron.

Strange particles

Strange particles as particles that are produced through the strong interaction and decay through the weak interaction (eg kaons).

Strangeness (symbol s) as a quantum number to reflect the fact that strange particles are always created in pairs.

Conservation of strangeness in strong interactions. Strangeness can change by 0, +1 or -1 in weak interactions.

Candidates will be expected to work out baryon numbers for individual particles and antiparticles from the information on the data sheet of the Baryon number of quarks

Lepton numbers and strageness quantum numbers are also given in the data pullout.


Candidates must gain an appreciation that particle physics relies on the collaborative efforts of large teams of scientists and engineers to validate new knowledge.

- recall that baryons and mesons are called hadrons and name two of each

- recall that baryons have 3 quarks

- recall that antibaryons have 3 antiquarks

- understand that hadrons are subject to the strong nuclear force whereas beta decay reactions are via the weak nuclear force

- know that mesons are made up of a quark and an antiquark and that the only strange particle you have to deal with (the one with a strangness quark) is the kaon

- know that the proton is the final stage of baryon decay

- appreciate the neutron into proton Feynman diagrams as representing that decay process (β- decay).

- recall the names of three leptons and understand that they are fundamental particles (do not break down into anything simpler)

AT k - Use of computer simulations of particle collisions.

AT i - Cosmic ray showers as a source of high energy particles including pions and kaons; observation of stray tracks in a cloud chamber; use of two Geiger counters to detect a cosmic ray shower. Quarks and antiquarks

Properties of quarks:
charge, baryon number and strangeness

Combinations of quarks and antiquarks required for baryons (proton and neutron only), antibaryons (antiproton and antineutron only) and mesons (pion and kaon only).

Only knowledge of up (u), down (d) and strange (s) quarks and their antiquarks will be tested.

The decay of the neutron should be known.

  - work out the quark composition of a given hadron, using the table of quark properties on the data sheet Applications of conservation laws

Change of quark character in β- decay and β+ decay

Application of the conservation laws for charge, baryon number, lepton number and strangeness to particle interactions. The necessary data will be provided in questions for particles outside those specified.

Students should recognise that energy and momentum are conserved in interactions.


- simplify the β- decay processes into quark interchange

- be able to work out what happens in a the following situations by using the conservation laws and the fact that in all of these the neutron changes into a proton or vice versa:

β- decay

β+ decay

electron capture

neutrino – neutron collisions

antineutrino – proton collisions

electron – proton collisions

Try atom builder - great fun!