X-Ray Tube Components and Principles

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Vocabulary flashcards covering major terms and definitions related to x-ray tube structure, operation, and safety.

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30 Terms

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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.

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External Components

Parts outside the glass envelope, including mounting supports and protective housing.

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Ceiling Support

Most common tube-mounting system allowing longitudinal and transverse travel along ceiling rails.

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Floor-to-Ceiling Support

Mount where the x-ray tube is attached to a vertical column anchored to both floor and ceiling.

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C-Arm Support

Mobile or fixed C-shaped mount that holds tube on one end and image receptor on the other.

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Protective Housing

Lead-lined enclosure that prevents electric shock, limits leakage radiation, provides mechanical support, and contains dielectric oil for heat dissipation.

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Leakage Radiation Limit

Maximum allowable radiation escaping housing: 1 mGy per hour at 1 m.

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Dielectric Oil

Insulating oil surrounding the tube inside housing; acts as electrical insulator and thermal cushion.

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Pyrex Glass Envelope

Heat-resistant glass enclosure of the tube that maintains vacuum and withstands high temperatures.

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Glass Window

5 cm² thin section of envelope through which the primary x-ray beam exits.

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Cathode

Negative electrode composed of filament(s) and focusing cup that supplies electrons for x-ray production.

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Filament

Small coil of thoriated tungsten heated to ~3400 °C to emit electrons by thermionic emission.

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Large vs. Small Filament

Dual-filament design providing choice of large or small focal spot for different imaging needs.

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Thermionic Emission

Release of electrons from heated filament forming space charge near the cathode.

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Space Charge

Cloud of electrons emitted from filament awaiting acceleration to anode.

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Focusing Cup

Negatively charged nickel container surrounding filament that electrostatically narrows electron beam.

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Anode

Positive electrode that attracts electrons and serves as the x-ray target; can be fixed or rotating.

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Fixed Anode

Stationary target surface used mainly in dental and portable units.

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Rotating Anode

Spinning target driven by induction motor, spreading heat over larger area to allow higher exposures.

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Target (Actual Focal Spot)

Area on the anode struck by electrons where x-rays are produced; made of rhenium-tungsten.

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Rhenium-Tungsten Target

Alloy giving high atomic number (74), excellent thermal conductivity, and 3400 °C melting point.

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Induction Motor

Electromagnetic motor that spins the rotating anode without physical contact; comprised of stator and rotor.

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Stator

Stationary electromagnets outside the envelope creating rotating magnetic field for induction motor.

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Rotor

Iron shaft with copper conductors inside envelope that turns the anode when energized by stator field.

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Line Focus Principle

Angling the anode (5–20°, typically 12°) so the actual focal spot is larger than effective focal spot, improving resolution.

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Effective Focal Spot

Apparent x-ray source size projected toward the patient; smaller than actual spot due to anode angle.

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Anode Heel Effect

Intensity variation in primary beam where anode side is up to 45 % less intense than cathode side.

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Tungsten Vaporization

Evaporation of tungsten from filament or anode that can plate the envelope and cause arcing—most common tube failure.

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Anode Cooling Chart (Rating Chart)

Graph showing heat storage capacity of anode to guide safe exposure techniques.

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Heat Unit (HU)

Quantity expressing thermal energy deposited in anode; Single-phase: kV × mAs × 0.7; Three-phase/HF: kV × mAs × 1.4