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Vocabulary flashcards covering major terms and definitions related to x-ray tube structure, operation, and safety.
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X-Ray Tube
Vacuum-sealed device in which electrons strike a target to produce x-rays; consists of cathode, anode, and supporting structure.
External Components
Parts outside the glass envelope, including mounting supports and protective housing.
Ceiling Support
Most common tube-mounting system allowing longitudinal and transverse travel along ceiling rails.
Floor-to-Ceiling Support
Mount where the x-ray tube is attached to a vertical column anchored to both floor and ceiling.
C-Arm Support
Mobile or fixed C-shaped mount that holds tube on one end and image receptor on the other.
Protective Housing
Lead-lined enclosure that prevents electric shock, limits leakage radiation, provides mechanical support, and contains dielectric oil for heat dissipation.
Leakage Radiation Limit
Maximum allowable radiation escaping housing: 1 mGy per hour at 1 m.
Dielectric Oil
Insulating oil surrounding the tube inside housing; acts as electrical insulator and thermal cushion.
Pyrex Glass Envelope
Heat-resistant glass enclosure of the tube that maintains vacuum and withstands high temperatures.
Glass Window
5 cm² thin section of envelope through which the primary x-ray beam exits.
Cathode
Negative electrode composed of filament(s) and focusing cup that supplies electrons for x-ray production.
Filament
Small coil of thoriated tungsten heated to ~3400 °C to emit electrons by thermionic emission.
Large vs. Small Filament
Dual-filament design providing choice of large or small focal spot for different imaging needs.
Thermionic Emission
Release of electrons from heated filament forming space charge near the cathode.
Space Charge
Cloud of electrons emitted from filament awaiting acceleration to anode.
Focusing Cup
Negatively charged nickel container surrounding filament that electrostatically narrows electron beam.
Anode
Positive electrode that attracts electrons and serves as the x-ray target; can be fixed or rotating.
Fixed Anode
Stationary target surface used mainly in dental and portable units.
Rotating Anode
Spinning target driven by induction motor, spreading heat over larger area to allow higher exposures.
Target (Actual Focal Spot)
Area on the anode struck by electrons where x-rays are produced; made of rhenium-tungsten.
Rhenium-Tungsten Target
Alloy giving high atomic number (74), excellent thermal conductivity, and 3400 °C melting point.
Induction Motor
Electromagnetic motor that spins the rotating anode without physical contact; comprised of stator and rotor.
Stator
Stationary electromagnets outside the envelope creating rotating magnetic field for induction motor.
Rotor
Iron shaft with copper conductors inside envelope that turns the anode when energized by stator field.
Line Focus Principle
Angling the anode (5–20°, typically 12°) so the actual focal spot is larger than effective focal spot, improving resolution.
Effective Focal Spot
Apparent x-ray source size projected toward the patient; smaller than actual spot due to anode angle.
Anode Heel Effect
Intensity variation in primary beam where anode side is up to 45 % less intense than cathode side.
Tungsten Vaporization
Evaporation of tungsten from filament or anode that can plate the envelope and cause arcing—most common tube failure.
Anode Cooling Chart (Rating Chart)
Graph showing heat storage capacity of anode to guide safe exposure techniques.
Heat Unit (HU)
Quantity expressing thermal energy deposited in anode; Single-phase: kV × mAs × 0.7; Three-phase/HF: kV × mAs × 1.4