<unk>  is<unk>  whose rays are nearly parallel, and therefore will spread slowly as it propagates. The word is derived from "collinear" and implies<unk>  that does not disperse with distance. A perfectly<unk>  beam with no divergence cannot be created due to diffraction, but<unk>  can be approximately<unk>  by a number of processes, for instance by means of a collimator.<unk>  is sometimes said to be focused at infinity. Thus as the distance from a point source increases, the spherical wavefronts become flatter and closer to plane waves, which are perfectly<unk> .
Collimated light
Synchrotron radiation
Electric current
Position 
Idose
Dose Profile
Oxygenation
Visual routine