nuclear definitions

• Rate of decay of radioactive nuclei in a given isotope is proportional to the total number of nuclei in the sample and is measured in Becquerels
• Alpha Decay:

  • Emission of an alpha particle (2 protons and 2 neutrons) from an unstable nucleus to make it more stable
  • Alpha radiation is strongly ionising and is stopped by a few centimetres of air or a sheet of paper
• Atomic Mass Unit:

  • Unit used to express atomic masses
  • One AMU is equal to one twelfth of the mass of a carbon atom
• Background Radiation:

  • Radiation found in small quantities from natural and man-made sources
  • Originates from rocks, cosmic rays, nuclear accidents, and medical sources
• Beta Decay:

  • Emission of a beta particle when a proton turns into a neutron (or vice versa) in an unstable nucleus
  • Beta minus radiation is weakly ionising, beta plus radiation is immediately annihilated by electrons
• Binding Energy:

  • Amount of energy required to split a nucleus into all its separate constituent nucleons
  • Equivalent to the mass defect
• Chain Reaction:

  • Neutrons released by a fission reaction induce further fissile nuclei to undergo fission
• Closest Approach:

  • Method of estimating a nuclear radius by firing an alpha particle at it
  • Involves calculating the distance at which all the alpha particle’s kinetic energy is converted to electric potential energy
• Contamination:

  • Introduction of radioactive material to another object, making it radioactive
• Control Rods:

  • Found in nuclear reactors to absorb neutrons and control the rate of reaction
  • Can be raised or lowered depending on the rate required
• Coolant:

  • Substance passing through nuclear reactors to remove heat from the core
  • Heat is then used to generate energy
• Critical Mass:

  • Smallest mass of fissile material required in a fission reactor for a chain reaction to be sustained
• Electron Capture:

  • Process in proton-heavy nuclei where an electron is drawn into the nucleus, causing a proton to transition into a neutron
  • Electron neutrino is also produced
• Fission:

  • Splitting of a nucleus to form two smaller daughter nuclei, neutrons, and energy
• Fusion:

  • Joining of two smaller nuclei to form a larger nucleus and release energy
• Gamma Decay:

  • Emission of gamma rays from an unstable nucleus with too much energy
  • Gamma radiation is weakly ionising and requires several centimetres of lead to be stopped
• Half-Life:

  • Average time for the number of radioactive nuclei in a sample to halve
• Inverse Square-Law:

  • Law governing the intensity of gamma radiation
  • Intensity of radiation at any point is inversely proportional to the square of the distance from its source
• Irradiation:

  • Exposure of an object to radiation without making the object radioactive
• Mass Defect:

  • Difference in mass between a nucleus and the sum of the masses of its constituent nucleons
• Moderator:

  • Material in nuclear reactors that absorbs energy from fast-moving neutrons to slow them down for fission
  • Induces fission by slowing down neutrons
• Radioactive Dating:

  • Use of radioactive isotopes with known half-lives to date objects
  • Carbon-14 is commonly used
• Radioactive Waste:

  • Waste produced from fission reactions, must be stored and handled carefully due to its instability
• Random Nature of Radioactive Decay:

  • Radioactive decay is random, cannot predict when or which nucleus will decay next
• Rutherford Scattering:

  • Experiment involving firing alpha particles at a thin gold foil and observing their deflections
  • Showed the existence and nature of the nucleus