Atomic Structure - Key Terms

• Atom


  the smallest quantity of an element that can take part in a chemical reaction, consisting of a positively charged nucleus made up of protons and neutrons, surrounded by negatively charged electrons
• Nucleus

  the positively charged, dense region at the centre of an atom, made up of protons and neutrons, orbited by electrons
• Proton


  a subatomic particle found in the nucleus of an atom, with an electrical charge of +1
• Neutron


  a neutral subatomic particle; a type of nuclear radiation, which can be emitted during radioactive decay
• Electron


  a subatomic particle, with a charge of -1, which orbits the nucleus of an atom
• Ion


  formed when an atom loses or gains one or more electrons to become charged
• Element

  a substance that consists only of atoms with the same number of protons in their nuclei
• Atomic number


  the number of protons in an atom of an element
• Isotopes


  atoms of the same element, but with different numbers of neutrons in the nucleus
• Unstable


  lacking stability; having a very short lifetime; radioactive
• Activity


  the rate at which a radioactive source emits radiation, measured in becquerels
• Radioactive


  containing a substance that gives out radiation
• Alpha


  a type of radiation, which is strongly ionising, in the form of a particle consisting of two neutrons and two protons (a helium nucleus)
• Beta


  a type of nuclear radiation that is moderately ionising, consisting of a high-speed electron, which is ejected from a nucleus as a neutron turns into a proton
• Gamma


  high frequency, short wavelength electromagnetic waves; a type of nuclear radiation, emitted from a nucleus
• Contamination

  the unwanted presence of materials containing radioactive atoms on other materials
• Irradiation


  to expose an object to nuclear radiation (the object does not become radioactive)
• Half-life


  the average time it takes for half the nuclei in a sample of radioactive isotope to decay; the time it takes for the count rate / activity of a radioactive isotope to fall by 50% (halve)
• Tracer


  a radioactive isotope that is put into a system so that its movement can be tracked, helping to reveal blockages / holes that should not be there; used in medicine and industry
• Fission


  the splitting of an atomic nucleus into parts, either spontaneously or as a result of the impact of a particle usually with an associated release of energy
• Chain reaction

  a process in which a neutron colliding with an atomic nucleus causes fission and the ejection of one or more other neutrons, which induce other nuclei to split
• Fusion


  a reaction in which two nuclei combine to form a nucleus with the release of energy