An atom or group of atoms with a positive or negative charge, either because of too few electrons (positive) or too many (negative). Electrically-charged atomic or molecular particle 1. A charged atom, usually of residual gas in an electron tube.

A spot on the fluorescent surface of a cathode ray tube that is somewhat darker than the surrounding area because of a bombardment by negative ions, which reduces the sensitivity.


1 Case, D., 1985, Motion Picture Film Processing, Media Manuals, Focal Press, London, Boston