unstable, An unstable nucleus in an atom is one that will decay and give out ionising radiation., radioactive decay, When an unstable nucleus changes by giving out ionising radiation to become more stable., random, Any process that cannot be predicted and can happen at any time is said to be random., alpha particle, A particle made of two protons and two neutrons, emitted as ionising radiation from some radioactive isotopes., beta particle, A particle of radiation emitted from the nucleus of a radioactive atom when it decays. It is an electron., gamma ray, A high-frequency electromagnetic wave emitted from the nucleus of a radioactive atom., penetrate, To go through., positron, The anti-particle of an electron, having the same mass but opposite charge. Positron emission is a type of beta decay., background radiation, Ionising radiation that is around us all the time from several sources. It can be naturally occurring, but some comes from human activities., cosmic rays, Charged particles with a high energy that come from stars, neutron stars, black holes and supernovae., count rate, The number of alpha or beta particles or gamma rays detected by a Geiger–Müller tube in a certain time., dose, The amount received at one time – for example, the amount of radiation a person receives., Geiger–Müller (GM) tube, A device that can detect ionising radiation and is used to measure the activity of a radioactive source., nuclear equation, An equation representing a change in an atomic nucleus due to radioactive decay. The atomic numbers and mass numbers must balance., activity, The number of emissions of ionising radiation from a sample in a given time. Activity is usually given in becquerels (Bq)., becquerel (Bq), The units for the activity of a radioactive object. One becquerel is one radioactive decay per second., half-life, The average time taken for half of the radioactive nuclei in a sample of radioactive material to have decayed (the activity halves)..

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