n. (Physics) A large and expensive scientific instrument used by physicists to accelerate elementary particles (such as protons or electrons) to speeds near that of light, for the purpose of investigating the fundamental properties of matter; sometimes also called an atom smasher, since the particles thus accelerated are often directed at targets of atoms which are fragmented by the impact into their more fundamental component particles. The particles generated by impact of a beam in an accelerator on its target are detected by various types of detecting apparatus, and procedures are required to sort and identify the many particles created. The fundamental particles generated by impacts in a particle accelerator are often those not actually present inside atoms; and in certain types of particle accelerator, such as the colliding beam accelerator, the impact which generates energetic particles is with other fundamental particles, and not with atoms. [ PJC ]