X-ray Tube Fundamentals - Vocabulary

Vocabulary flashcards covering core terms and definitions from the lecture notes on X-ray tubes and high-voltage systems.

Electromagnetic radiation

Energy that travels as waves; X-rays are a form of electromagnetic (EM) radiation.

X-ray

High-energy electromagnetic radiation produced when fast electrons strike a target.

Ionizing radiation

Radiation energetic enough to remove electrons from atoms.

ALARA

As Low As Reasonably Achievable; principle to minimize radiation exposure.

Four essential conditions for producing X-rays

Source of free electrons; means to accelerate them; means to decelerate them on a target; and a vacuum.

Thermionic emission

Emission of electrons from a heated filament.

X-ray tube

Vacuum tube containing cathode and anode that produces X-rays when electrons hit the target.

Cathode

Negatively charged electrode that emits electrons and contains the filament and focusing cup.

Anode

Positively charged electrode that attracts electrons; contains the target on the disc.

Filament

Tungsten wire heated to emit electrons; may be doped with thorium to improve emission.

Focusing cup

Negative structure that constrains the electron cloud toward the anode.

Glass envelope

The glass enclosure that maintains the tube vacuum and houses components.

Vacuum

Empty space inside the X-ray tube to prevent electron interactions with matter.

Target

The hit surface on the anode where electrons produce X-rays; typically tungsten-based.

Anode disc

Rotating disc that bears the target; helps dissipate heat.

Anode stem

Support/shaft that conducts heat away from the anode.

Stator

Stationary coil that powers the induction motor portion of the tube.

Rotor

Rotating part turned by the stator to spin the anode assembly.

Shaft

Anode shaft; part of the mechanical support connecting rotor to the anode.

Target material (tungsten)

Primary material for the X-ray target due to high atomic number and melting point.

Molybdenum and graphite

Backing materials in the anode assembly to aid heat dissipation.

Rhenium

Material added to tungsten target for durability and heat handling.

Thorium

Dopant added to the filament to improve thermionic emission and life.

Graphite

Material used in target assembly backing for heat conduction.

Small focal spot vs large focal spot

Two filament sizes; small for高 spatial resolution, large for higher current (MA).

Heat capacity

Ability to absorb heat without damage; important for rotating vs stationary anodes.

Step-up transformer

Transformer that increases voltage from the low-voltage to the high-voltage side.

Auto transformer

Autotransformer used to select the kilovoltage peak (kVp) fed to the high-voltage circuit.

Primary side / Secondary side

Sides of a transformer: primary receives input, secondary provides output.

Low voltage side / High voltage side

Low voltage side powers the filament/control circuits; high voltage side supplies the X-ray tube.

Rectifier

Device that converts alternating current (AC) to direct current (DC) for tube operation.

Rectification

The process of converting AC to DC in the X-ray tube circuit.

Three-phase generator

Power supply with more stable voltage/less ripple; more efficient X-ray production.

Single-phase generator

Older, less efficient generator with greater voltage ripple.

Kilovoltage peak (kVp)

Peak voltage applied across the X-ray tube; controls photon energy.

mA (milliampere)

Unit of tube current; controls the number of electrons emitted per unit time.

Ohm’s law

V = I × R; relationship between voltage, current, and resistance.

Coulombs

Unit of electric charge.

Input phosphor

Phosphor material at the input of a fluoroscopic or X-ray device (cesium iodide, etc.).

Cesium iodide (CsI)

Phosphor material used in input screens to convert X-rays to light; common in detectors.

Gadolinium oxybromide (GdOBr)

Phosphor material used in image intensification/display systems.

Barium fluorohalide

Phosphor material used in screens to convert X-ray energy to light.

Focusing cup charge

Negative charge around the filament to focus electron flow toward the anode.

Leakage radiation

Radiation escaping from the tube housing due to imperfect shielding.

Heat dissipation in housing

Oil bath and housing structure help dissipate heat from the tube.

Rotating anode RPM

Speed of the anode rotation (typical ~3,500 rpm; high-speed ~10,000 rpm) to spread heat.

Rotating vs stationary anode

Rotating anode provides greater heat dissipation and larger target area.

Spatial resolution

Ability to distinguish fine details; higher with small focal spot.