Exam Review: Radiation and the X-ray Tube - Vocabulary Flashcards

A comprehensive set of vocabulary flashcards covering key concepts, terms, and definitions from the lecture notes on radiation and the X-ray tube.

Atom

The smallest unit of an element that retains all of its chemical properties.

Electron shells

Energy levels around the nucleus labeled K, L, M, N from inside to outside.

Maximum electrons in a shell

2n^2, where n is the shell number.

Isotope

Atoms with the same number of protons (Z) but different numbers of neutrons.

Isotone

Atoms with the same number of neutrons.

Isobar

Atoms with the same mass number (A) but different proton/neutron composition.

Isomer

Same nucleus in an excited (higher energy) state.

Atomic number (Z)

Number of protons in the nucleus; identifies the element.

Mass number (A)

Total number of nucleons (protons + neutrons).

Proton

Positively charged nucleon located in the nucleus.

Neutron

Electrically neutral nucleon in the nucleus.

Electron

Negatively charged subatomic particle orbiting the nucleus.

Speed of light (c)

Constant speed of electromagnetic radiation in vacuum; approximately 3 x 10^8 m/s.

Velocity units

Meters per second (m/s).

Wavelength units

Meters (m).

Frequency unit (Hertz)

Hz; one cycle per second.

Wave equation (V = f × λ)

Relation between velocity, frequency, and wavelength for waves.

Frequency–wavelength relationship

For a given velocity, frequency and wavelength are inversely related.

Electromagnetic spectrum order

From high energy to low: cosmic, gamma, X-ray, ultraviolet, visible, infrared, microwaves, radio.

Speed of EM radiation (c)

The constant speed at which electromagnetic waves travel in vacuum.

Photon

The quantum of electromagnetic radiation; a particle and a wave.

Photon properties

Travel in vacuum, excite/ionize matter, velocity c, wave–particle duality.

Hertz

Unit of frequency; 1 Hz = 1 cycle per second.

The X-ray tube

Device that produces X‑rays by accelerating electrons toward a target.

Thermionic emission

Ejection of electrons from a heated filament.

Filament materials

Best: thoriated tungsten; also molybdenum and rhenium are acceptable.

Filament

Wire in the cathode that emits electrons when heated.

Focusing cup

Negatively charged cup that compresses the electron cloud toward the anode.

Negative charge in normal operation

Focusing cup is biased negative relative to the filament.

Positive charging of focusing cup (grid control)

Focusing cup becomes positive when used as a switch to turn off emission.

Cathode assembly

Main parts: filament and focusing cup.

Filament material considerations

High melting point and suitable temperature for thermionic emission.

Anode disk layers

1) Tungsten‑rhenium alloy (x-ray production) 2) Molybdenum disk (support/heat dissipation) 3) Graphite backing (prevents warping and heat transfer to rotor)

Anode materials

High atomic number, high melting point, high heat-conducting ability.

X-ray tube components: Rotor

Rotates the anode; supported inside the tube.

X-ray tube components: Stator

Outside the glass envelope; electromagnets that drive the rotor.

Glass envelope

Vacuum-sealed housing containing the tube components.

Thermionic emission location

Filament inside the cathode.

Photon production location

Anode (actual focal spot) where accelerating electrons produce X‑rays.

Vacuum (in the envelope)

Space from which air has been removed to prevent arcing and allow X‑ray production.

Induction motor

Motor that rotates the anode by electromagnetic induction (no physical contact).

Rotor and Stator

The rotating (rotor) and stationary (stator) parts of the induction motor.

Line-focus principle

The relationship between actual focal spot, effective focal spot, and anode angle.

Actual focal spot

The physical area of the anode that electrons hit.

Effective focal spot

The projected size of the focal spot on the image; usually smaller than the actual spot.

Filament size effect

Larger filament yields a larger effective focal spot.

Anode target angle effect

Smaller angles reduce the effective focal spot size.

Dual focus tube

X-ray tube with two filaments for two focal spots.

Fat Cat concept

The thicker side of the tube housing (under the cathode) to account for beam distribution.

Rotation speeds

Regular anodes ~3600 rpm; high‑capacity ~10,000 rpm.

Heat dissipation factors

Disk diameter, disk rpm, and line‑focus angle help dissipate heat.

Ionization

Removal of an electron from an atom.

Target angle

Typical angle around 12 degrees (range ~5–15 degrees) in most tubes.

Space charge

Accumulation of electrons in the area around the filament.

Anode positive, cathode negative

Anode is positive; cathode is negative (source of electrons).

Tube housing

Steel housing containing dielectric oil and lead lining.

Dielectric oil

Insulates and cools; prevents electrocution inside the tube.

Dielectric oil purposes

Insulation to prevent shock and cooling of the tube.

Biased tube

Focusing cup is more negative than the filament to modulate emission.

Isotropic emission

X‑rays are emitted in all directions; housing lead lining blocks most except the useful direction.

Leakage radiation limit

Maximum permissible leakage radiation: 100 mR/hr at 1 meter.

Vacuum

A space from which air has been removed.

X-ray production process

Heating filament → thermionic emission → electrons accelerate to anode → braking/characteristic interactions release X‑rays.

Tungsten (W) in X‑ray tubes

Preferred due to high atomic number (Z) and high melting point.

Computed tomography development year

CT was developed in the 1970s.

Anode heel effect

Variation in exposure across the beam due to the anode’s angle.

Extrafocal (off‑focus) radiation

Photons emitted from areas other than the focal spot.

Collimator mirror function

Reflects light to help visualize the field size and position.

Filament length (typical)

Approximately 1–3 mm long.

L‑shell electrons (Z = 22)

Second principal energy level can hold up to 8 electrons.

SI unit for length

Meter (m).

Positive end of the X‑ray tube

Anode.

Anode heel effect exposure pattern

Can cause decreased exposure toward the anode end of the beam.

X‑ray window

The portion of the tube housing through which X‑rays exit.

Roentgen discovery

Discovered x‑rays while experimenting with Crookes tube.