ABSTRACT
(Diagnostic Radiology) A vacuum is an empty space. The name is derived from the Latin, vacuus, meaning empty. Most electronic tubes, including x-ray and image intensifier tubes, are evacuated, so there is no air or other gases to impede the passage of electrons. Vacuum is measured as pressure in pascals (SI unit, 1 Pa = 1 N/m2) or in bars (1 bar = 100 kPa). For example, the vacuum in an x-ray tube is minimum 10−6 mbar. It is necessary so as not to impede the flow of electrons, usually from a cathode to an anode.
