X-Ray Tube Components and Principles

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

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