AQA GCSE Physics – Atomic structure

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activity
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the number of unstable atoms that decay per second in a radioactive source
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alpha radiation (α)
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alpha particles, each composed of two protons and two neutrons, emitted by unstable nuclei
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atomic number
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the number of protons (which equals the number of electrons) in an atom. It is sometimes called the proton number
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beta radiation (β)
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beta particles that are high energy electrons created in, and emitted from, unstable nuclei
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chain reaction
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reactions in which one reaction causes further reactions, which in turn cause further reactions, etc.
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count rate
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the number of counts per second detected by a Geiger counter
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gamma radiation (γ)
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electromagnetic radiation emitted from unstable nuclei in radioactive substances
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half life
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average time taken for the number of nuclei of the isotope (or mass of the isotope) in a sample to halve
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ionisation
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any process in which atoms become charged
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irradiated
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an object that has been exposed to ionising radiation
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isotopes
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atoms with the same number of protons and different numbers of neutrons
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mass number
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the number of proton and neutrons in a nucleus
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moderator
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substance in a nuclear reactor that slows down fission neutrons
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nuclear fission
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the process in which certain nuclei (uranium-235 and plutonium-239) split into two fragments, releasing energy and two or three neutrons as a result
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nuclear fission reactor
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reactors that release energy steadily due to the fission of a suitable isotope, such as uranium-235
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nuclear fusion
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the process where small nuclei are forced together to fuse and form a larger nucleus
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radioactive contamination
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the unwanted presence of materials containing radioactive atoms on other materials
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reactor core
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the thick steel vessel used to contain fuel rods, control rods and the moderator in a nuclear fission reactor

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