A level AQA Physics - Particles (Key Definitions)

Alpha Decay

The process of an unstable nucleus emitting an alpha particle (two protons and two neutrons) to become more stable.

Annihilation

The process of a particle and its antiparticle colliding and being converted into energy, released in two photons to conserve momentum.

Antiparticle

All particles have a corresponding antiparticle with the same mass but opposite charge and conservation numbers.

Baryon Number

A quantum number that is conserved in all particle interactions; baryons have a baryon number of +1 and non-baryons have a baryon number of 0.

Baryon

A class of hadron that is made up of three quarks; the proton is the only stable baryon.

Beta-Minus Decay

The process of a neutron turning into a proton, emitting a beta-minus particle (electron) and an antineutrino.

Beta-Plus Decay

The process of a proton turning into a neutron, emitting a beta-plus particle (positron) and a neutrino.

Electron Diffraction

The spreading of electrons as they pass through a gap similar to the magnitude of their de Broglie wavelength, evidence of wave-like properties of particles.

Electron-volt (eV)

The work done to accelerate an electron through a potential difference of 1V; 1eV is equivalent to the charge of an electron (E=qv).

Energy Levels

Defined and distinct energies at which electrons can exist in an atom; an electron cannot exist between energy levels.

Excitation

The process of an electron taking in exactly the right quantity of energy to move to a higher energy level.

Gauge Boson

The exchange particles that transmit the four fundamental interactions between particles.

Ground State

The most stable energy level that an electron can exist in.

Hadrons

A class of subatomic particles that experience the strong nuclear interaction.

Ionisation

The process of an atom losing an orbital electron and becoming charged.

Isotope

Same number of protons but different numbers of neutrons.

Isotopic Data

Data from isotopes that can be used for a purpose, such as carbon dating.

Kaon

A type of meson that decays into pions.

Lepton Number

A quantum number that is conserved in all particle interactions, including both electron lepton numbers and muon lepton numbers.

Lepton

A group of elementary subatomic particles, which includes electrons, muons, and neutrinos.

Meson

A class of hadron that is made up of a quark and an antiquark pair.

Muon

A type of lepton that decays into electrons.

Neutrino

A subatomic particle whose existence was hypothesised to maintain the conservation of energy in beta decay.

Nucleon Number (A)

The sum of the number of protons and neutrons in a given nucleus.

Nucleon

A proton or neutron.

Pair Production

The process of a high-energy photon converting into a particle and its corresponding antiparticle, usually occurring near a nucleus.

Photon

A packet of energy.

Pion

A type of meson and the exchange particle for the strong nuclear force.

Positron

A positively charged particle that is the antiparticle of an electron.

Proton Number (Z)

The number of protons present in the nucleus of a given element.

Stopping Potential

The minimum potential difference required to stop the highest kinetic energy electrons from leaving the metal plate in the photoelectric effect.

Strange Particles

Particles that are produced through the strong interaction but decay through the weak interaction.

Strangeness

A quantum number conserved in strong interactions but not in weak interactions; strange particles are always produced in pairs.

Strong Nuclear Force

A force that acts between nucleons in a nucleus to keep it stable, attractive at distances up to 3fm and repulsive at separations less than 0.5fm.

Threshold Frequency

The minimum frequency of photons required for photoelectrons to be emitted from the surface of a metal plate through the photoelectric effect.

Work Function

The minimum energy required to remove an electron from a metal’s surface.