Dental Radiography: Radiation Physics

Vocabulary practice flashcards covering fundamental concepts of atomic structure, radiation physics, x-ray tube components, electrical circuits, and x-ray interactions with matter based on Chapter 2.

Matter

Anything that occupies space and has mass.

Atom

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

Mass number

The number of protons and neutrons in the nucleus of an atom, which determines its atomic weight.

Atomic number

The number of protons inside the nucleus of an atom, which equals the number of electrons outside the nucleus.

Electrons

Tiny, negatively charged particles with very little mass (approximately $\frac{1}{1800}$ as much as a proton or neutron) that travel around the nucleus in orbits or shells.

Binding energy

The electrostatic force between the positive nucleus and negative electrons that maintains electrons in their orbits, measured in electron volts or kilo electron volts.

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.

Ion pair

The pair formed when an electron is removed from an atom; consists of the positive ion (the atom) and the negative ion (the ejected electron).

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.

Ionizing radiation

Radiation capable of producing ions by removing or adding an electron to an atom, classified into particulate and electromagnetic radiation.

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 originating in an x-ray tube.

Alpha particles

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

Electromagnetic radiation

The propagation of wavelike energy (without mass) through space or matter, featuring oscillating electric and magnetic fields positioned at right angles to one another.

Photons

Discrete bundles of energy with no mass or weight that travel as waves at the speed of light in a straight line, also called quanta.

Velocity

In wave concept, the speed of the 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 consisting of weightless bundles of energy without an electrical charge.

Control panel

A component of the x-ray machine that contains an on-off switch, indicator light, and control devices for time, kilovoltage, and milliamperage.

Extension arm

A component that suspends the x-ray tubehead, houses electrical wires from the control panel, and allows for movement and positioning.

Tubehead

A tightly sealed, heavy metal housing that contains the x-ray tube, transformers, insulating oil, tubehead seal, aluminum disks, lead collimator, and PID.

Insulating oil

Oil surrounding the x-ray tube and transformers inside the tubehead that prevents overheating.

Aluminum disks

Disks positioned in the tubehead to filter out nonpenetrating, longer wavelength x-rays.

Lead collimator

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

Position-indicating device (PID)

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

Cathode

The negative electrode in an x-ray tube consisting of a tungsten wire filament and a molybdenum cup; supplies the electrons needed to generate x-rays.

Anode

The positive electrode in an x-ray tube consisting of a wafer-thin tungsten plate embedded in a solid copper rod; converts electrons into x-ray photons.

Direct current (DC)

Electrical flow in which electrons travel in one direction through a conductor.

Alternating current (AC)

Electrical flow in which electrons travel in two opposite directions.

Rectification

The conversion of alternating current to direct current.

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 causing electrons to move from a negative pole to a positive pole, measured in volts (V) or kilovolts (kV).

Filament circuit

A circuit that uses $3\text{ to }5\text{ volts}$ to regulate the flow of electrical current to the cathode filament, controlled by milliampere settings.

High-voltage circuit

A circuit that uses $65,000\text{ to }100,000\text{ volts}$ to provide the voltage required to generate x-rays, controlled by kilovoltage settings.

Step-down transformer

A device used to decrease incoming line voltage to the $3\text{ to }5\text{ volts}$ used by the filament circuit, featuring more coils in the primary coil than in the secondary coil.

Step-up transformer

A device used to increase incoming voltage to the $65,000\text{ to }100,000\text{ volts}$ used by the high-voltage circuit, featuring more coils in the secondary coil than in the primary coil.

Autotransformer

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

Thermionic emission

The release of electrons from the tungsten filament when it is heated by the filament circuit.

General radiation

X-radiation produced when an electron hits or passes close to the nucleus of a tungsten atom; accounts for approximately $70\text{\%}$ of x-rays produced.

Characteristic radiation

X-radiation produced when a high-speed electron dislodges an inner-shell electron from a tungsten atom, occurring only at $70\,\text{kV}$ and above.

Primary radiation

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

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 where an x-ray photon collides with a tightly bound inner-shell electron, giving up all its energy to eject the electron from orbit.

Compton scatter

An interaction where an x-ray photon collides with a loosely bound outer-shell electron, gives up part of its energy to eject the electron, and continues in a different direction at a lower energy level.

Coherent scatter

An interaction in which a low-energy x-ray photon interacts with an outer-shell electron and has its path altered without causing changes to the atom or producing ionization.