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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