definitions and concepts

• activity

  the rate of decay of the radioactive nuclei in a given isotope

  • proportional to the total number of nuclei in the sample and is measured in becquerels
• alpha decay

  the emission of an alpha particle from an unstable nucleus to make it more stable

  • usually form a nucleus of too much mass
  • alpha radiation is strongly ionising and is stopped by a few centimetres of air or a sheet of paper
• atomic mass unit

  a unit used to express atomic masses

  • one AMU is equal to one twelfth of the mass of a carbon atom
• background radiation

  radiation that is found in small quantities everywhere

  • originated from natural sources, such as rocks, and cosmic rays
  • also found in man-made sources such as nuclear accidents and medical sources
• beta decay

  the 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

  the amount of energy required to split a nucleus into all of its separate constituent nucleons

  • equivalent to the mass defect
• chain reaction

  the process of the neutrons released by a fission reaction inducing further fissile nuclei to undergo fission
• closest approach

  a 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

  the introduction of radioactive material to another object

  • the object is consequently radioactive
• control rods

  rods found in nuclear reactors to absorb neutrons and control the rate of reaction

  • they can be raised or lowered depending on the rate required
• coolant

  a substance that passes through nuclear reactors and is responsible for removing heat from the core

  • this heat is then used to generate energy
• critical mass

  the smallest mass of fissile material required in a fission reactor for a chain reaction to be sustained
• electron capture

  a process that occurs in proton-heavy nuclei, in which an electron is drawn into the nucleus, causing a proton to decay into a neutron

  • produces an electron neutrino
• fission

  the splitting of a nucleus to form two smaller daughter nuclei, neutrons, and energy
• fusion

  the joining of two smaller nuclei to form a larger nucleus and release energy
• gamma decay

  the emission of gamma rays from an unstable nucleus that has too much energy

  • very weakly ionising but required several centimeters of lead to be stopped
• half-life

  the average time it takes for the number of radioactive nuclei in a sample to half
• inverse square law

  a law that governs the intensity of gamma radiation

  • the intensity of radiation at any point is inversely proportional to the square of the distance from its source
• irradiation

  the exposure of an object to radiation

  • the exposed object does not become radioactive
• mass defect

  the difference in mass between a nucleus and the sum of the masses of its constituent nucleons
• moderator

  a material in nuclear reactors that absorbs energy from fast moving neutrons to slow them down to speeds that can be absorbed by fissile neutrons to induce fission
• radioactive dating

  the use of radioactive isotopes with known half-lives to date objects

  • usually uses isotope carbon-14
• radioactive waste

  the waste produced from the products of fission reaction

  • as the waste is unstable and radioactive, it must be stored and handled carefully
• random nature of radioactive decay

  radioactive decay is random

  • cannot predict when a nucleus will decay or which nucleus will decay next
• rutherford scattering

  an experiment involving firing alpha particles at a thin gold foil and observing their deflections

  • showed the existence and nature of the nucleus