Particles and Radiation definitions

AQA A Level Physics

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. The energy is 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 inside a nucleus turning into a proton, and emitting a beta-minus particle (an electron) and a antineutrino

Beta-Plus Decay

The process of a proton inside a nucleus turning into a neutron, and emitting a beta-plus particle (a 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. It is evidence of the wave-like properties of particles

Electron-volt (eV)

The work done to accelerate an electron through a potential difference of 1V. 1eV is equal 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 particle that experiences 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. Both electron lepton numbers and muon lepton numbers must be conserved

Lepton

A group of elementary subatomic particles, consisting of electrons, muons and neutrinos

Meson

A class of hadron that is made up of a quark and 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 sufficiently high-energy photon converting into a particle and its corresponding antiparticle. To conserve momentum, this usually occurs 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 that is conserved in strong interactions but not in weak interactions. This reflects that strange particles are always produced in pairs

Strong Nuclear Force

A force that acts between nucleons in a nucleus to keep it stable. It is attractive at distances of 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. It is equal to the metal’s work function divided by Planck’s constant

Work Function

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