Definitions: 2. Particles and Radiation

• 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 1 V. 1 eV 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 3 fm and repulsive at separations less than 0.5 fm.
• 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.