atom - This consists of protons (positively charged) and neutrons (no charge) which are contained in the nucleus surrounded by orbiting electrons (negatively charged)., ionisation - The process whereby an atom gains or loses an electron., alpha particle - A helium nucleus consisting of 2 protons and 2 neutrons., beta particle - A fast moving electron that is ejected from the nucleus of an atom undergoing nuclear decay., gamma ray - An electromagnetic wave of high frequency., activity - The number of nuclei decaying per second (i.e. the rate of nuclei decaying)., background radiation - Ionising radiation which is present all the time and can be natural or artificial in nature., absorbed dose - The energy absorbed per unit mass of the absorbing material. , radiation weighting factor - Each type of ionising radiation has differing levels of ionisation densities. To take account of this and also of the biological effects of ionising radiation, this is assigned to each type of ionising radiation., equivalent dose - The product of absorbed dose and radiation weighting factor. , equivalent dose rate - The equivalent dose per unit time. , half-life - The time it takes for activity of the radioactive source to decrease to half of its original value., nuclear fission - When a nucleus of large mass number splits into two daughter nuclei of smaller mass number releasing energy and often some neutrons., nuclear fusion - When two nuclei of smaller mass number join together to create a larger nucleus of greater mass number. This also causes heat energy to be released., chain reaction - Neutrons released by a nuclear reaction go on to produce further fission reactions., fuel rods - These are made of uranium-238 enriched with uranium-235 which produces energy by nuclear fission., moderator - This is normally made of graphite and has the fuel rods embedded within it. Its purpose is to slow down neutrons that are produced in fission, since a nucleus is split more easily by slow moving neutrons., control rods - These are normally made of boron, absorb neutrons so by lowering them into the reactor, the reaction can be slowed down. In the event of an emergency they are pushed right into the core of the reactor and the chain reaction stops completely., coolant - A cooling system is needed to cool the reactor and to transfer heat to the boilers in order to generate electricity. British gas-cooled reactors use carbon dioxide gas as a coolant., containment vessel - The containment vessel is made of thick concrete which acts as a shield to absorb neutrons and other radiations.,

National 5 Physics Radiation Definitions

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