Dental Radiography - Radiation Physics Vocabulary

Vocabulary flashcards covering atomic structure, electromagnetic radiation, x-ray tube components, circuitry, production mechanisms, and radiation interactions based on Chapter 2.

Matter

Anything that occupies space and has mass; when altered, energy results.

Atom

The fundamental unit of matter, composed of a central nucleus and orbiting electrons.

Nucleus

The central portion of an atom composed of positively charged protons and uncharged neutrons.

Protons

Subatomic particles that carry positive electrical charges and are located in the nucleus.

Neutrons

Subatomic particles that carry no electrical charge and are located in the nucleus.

Electrons

Tiny, negatively charged particles that orbit the nucleus with very little mass, approximately $\frac{1}{1800}$ as much as a proton or neutron.

Binding energy

The electrostatic force maintaining electrons in their orbits, determined by the distance between the nucleus and the orbiting electron (strongest in the K shell).

Molecule

Two or more atoms joined by chemical bonds, or the smallest amount of a substance that possesses its characteristic properties.

Ion

An atom that gains or loses an electron and becomes electrically unbalanced.

Ionization

The production of ions, or the process of converting an atom into ions by adding or removing an electron.

Ion pair

A pair consisting of a positive ion (the atom) and a negative ion (the ejected electron) resulting from ionization.

Radiation

The emission and propagation of energy through space or a substance in the form of waves or particles.

Radioactivity

The process by which certain unstable atoms or elements undergo spontaneous disintegration, or decay, in an effort to attain a more balanced nuclear state.

Particulate radiation

Tiny particles of matter that possess mass and travel in straight lines at high speeds.

Beta particles

Fast-moving electrons emitted from the nucleus of radioactive atoms.

Cathode rays

Streams of high-speed electrons that originate in an x-ray tube.

Alpha particles

Particles emitted from the nuclei of heavy metals, existing as two protons and neutrons without electrons.

Electromagnetic radiation

The propagation of wavelike energy (without mass) through space or matter in oscillating electric and magnetic fields positioned at right angles.

Photon

A discrete bundle or packet of pure electromagnetic energy with no mass or weight that travels in waves at the speed of light.

Velocity

The speed of a wave.

Wavelength

The distance between the crest of one wave and the crest of the next.

Frequency

The number of wavelengths that pass a certain point in a given length of time.

X-radiation

High-energy, ionizing electromagnetic radiation.

X-rays

Weightless bundles of energy without an electrical charge that travel in waves with a specific frequency at the speed of light.

Control panel

The component of an x-ray machine containing an on-off switch, indicator light, and control devices for time, kilovoltage, and milliamperage.

Extension arm

The component of an x-ray machine that suspends the tubehead, houses electrical wires, and allows movement and positioning of the tubehead.

Tubehead

A tightly sealed, heavy metal housing containing the x-ray tube, insulating oil, transformers, aluminum disks, lead collimator, and position-indicating device.

Insulating oil

Oil that surrounds the x-ray tube and transformers inside the tubehead to prevent overheating.

Aluminum disks

Disks located in the path of the x-ray beam that filter out nonpenetrating, longer wavelength x-rays.

Lead collimator

A lead diaphragm that restricts the size and shape of the x-ray beam.

Position-indicating device (PID)

An open-ended cylinder or rectangular device that aims and shapes the x-ray beam.

Cathode

The negative electrode in the x-ray tube, consisting of a tungsten filament and a molybdenum cup, which supplies the electrons necessary to generate x-rays.

Anode

The positive electrode in the x-ray tube, consisting of a tungsten target embedded in a solid copper rod, which converts electrons into x-ray photons.

Tungsten filament

A coiled wire in the cathode that emits electrons when heated.

Molybdenum cup

A holder in the cathode that focuses electrons into a narrow beam directed toward the tungsten target.

Tungsten target

A focal spot on the anode that converts colliding electrons into x-ray photons.

Copper stem

A solid copper rod in the anode that functions to dissipate heat away from the tungsten target.

Thermionic emission

The release of electrons from the tungsten filament when heated by electrical current.

Direct current (DC)

An electrical current in which electrons flow in one direction through a conductor.

Alternating current (AC)

An electrical current in which electrons flow in two opposite directions.

Rectification

The conversion of alternating current ($AC$) to direct current ($DC$).

Amperage

The measurement of the number of electrons moving through a conductor, measured in amperes ($A$) or milliamperes ($mA$).

Voltage

The measurement of electrical force that causes electrons to move from a negative pole to a positive one, measured in volts ($V$) or kilovolts ($kV$).

Step-down transformer

A device used to decrease line voltage from $110$ or $220$ volts to the $3\text{ to }5$ volts used by the filament circuit.

Step-up transformer

A device used to increase incoming voltage to the $65,000\text{ to }100,000$ volts used by the high-voltage circuit.

Autotransformer

A voltage compensator that corrects for minor fluctuations in electrical current.

General radiation

Also known as braking radiation or bremsstrahlung, x-rays produced when an electron hits or passes close to the nucleus of a tungsten atom (accounts for about $70\%$ of dental x-rays).

Characteristic radiation

X-radiation produced at $70\,kVp$ and above when a high-speed electron dislodges an inner-shell electron from a tungsten atom, causing ionization and orbital rearrangement.

Primary radiation

The penetrating x-ray beam produced at the target of the anode that exits the tubehead.

Secondary radiation

X-radiation created when the primary beam interacts with matter.

Scatter radiation

A form of secondary radiation resulting from an x-ray photon deflected from its path by interaction with matter.

Photoelectric effect

An interaction in which an x-ray photon collides with a tightly bound inner-shell electron, giving up all its energy to eject the photoelectron and being completely absorbed ($30\%$ of interactions).

Compton scatter

An interaction in which an x-ray photon collides with a loosely bound outer-shell electron, ejecting a Compton electron and scattering the lower-energy photon in a new direction ($62\%$ of interactions).

Coherent scatter

An interaction in which a low-energy x-ray photon has its path altered by an outer-shell electron without causing ionization or energy change ($8\%$ of interactions).