Radiation Physics, Biology, and Protection

Comprehensive vocabulary flashcards covering the principles of atomic structure, x-ray production, beam characteristics, dental radiography interactions, radiation biology, and safety protocols based on the lecture transcript.

Matter

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

Atom

The fundamental unit of matter, composed of tiny invisible particles.

Nucleus

The dense core of an atom, composed of protons and neutrons, occupying very little space compared to the entire atom.

Protons

Particles within the nucleus that carry positive electrical charges.

Neutrons

Particles within the nucleus that carry no electrical charge.

Atomic number (Z)

The number of protons inside the nucleus, which equals the number of electrons in a neutral atom and determines the identity of the element.

Mass number (A)

The total number of protons and neutrons in the nucleus of an atom; also referred to as atomic weight.

Electrons

Tiny, negatively charged particles that revolve around the nucleus in orbits or shells; an electron weighs approximately $\frac{1}{1800}$ as much as a proton.

Binding energy

The electrostatic force or attraction between the positive nucleus and negative electrons that maintains electrons in their orbits.

Electron volts (eV)

The unit of measurement for binding energies of orbital electrons; one kilo electron volt ($1000$ electron volts) is denoted as $keV$.

Ionization

The process of forming an ion pair where a neutral atom loses an electron, becoming a positive ion, while the ejected electron becomes a negative ion.

Ionizing radiation

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

Particulate radiation

Tiny particles of matter that possess mass, travel in straight lines, and move at high speeds, such as alpha particles and electrons (beta particles or cathode rays).

Electromagnetic radiation

The movement of energy through space as a combination of electric and magnetic fields, such as x-rays, gamma rays, and visible light.

Photons

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

Velocity

The speed of an electromagnetic wave, which is the speed of light, approximately $3 imes 10^8\text{ meters per second}$ in a vacuum.

Wavelength

The distance between the crest of one wave and the crest of the next; it determines the energy and penetrating power of the radiation.

Frequency

The number of wavelengths that pass a given point in a certain amount of time; it is inversely related to wavelength.

X-rays

Weightless bundles of energy (photons) without an electrical charge that travel in waves at a specific frequency at the speed of light and can cause ionization.

Cathode

The negative electrode in the x-ray tube consisting of a tungsten filament and a molybdenum focusing cup.

Anode

The positive electrode in the x-ray tube consisting of a tungsten target embedded in a copper stem.

Thermionic emission

The release of electrons from the tungsten filament when it is heated to incandescence by an electrical current.

Tungsten target

An anode component with a high atomic number ($74$) and high melting point ($3422^\circ\text{C}$) designed to convert kinetic energy of electrons into x-ray photons.

Focal spot

The specific area on the tungsten target where electrons are directed and x-rays are produced; a smaller effective focal spot increases image sharpness.

Kilovoltage peak (kVp)

The maximum or peak voltage of an alternating current, controlling the speed of electrons and the quality or penetrating power of the x-ray beam.

Milliamperage (mA)

The measurement of the x-ray tube current, which regulates the temperature of the filament and the quantity (number) of x-rays produced.

Filtration

The use of aluminum disks to preferentially remove low-energy, non-penetrating x-ray photons from the beam path.

Collimator

A lead plate with a central hole that restricts the size and shape of the x-ray beam as it exits the tubehead.

Bremsstrahlung radiation

Also called 'braking radiation,' it is produced when high-speed electrons are slowed down or stopped by the tungsten nuclei in the target.

Characteristic radiation

Radiation produced when an incident electron ejects an inner-shell electron from a target atom, and an outer-shell electron drops into the vacancy.

Coherent scattering

An interaction where a low-energy photon's path is altered by an atom without a change in energy or the production of ionization; accounts for about $7\%$ of dental x-ray interactions.

Compton scattering

An interaction where an x-ray photon collides with an outer-shell electron, ejecting it (recoil electron) and scattering the photon in a new direction with lower energy; accounts for about $57\%$ of dental x-ray interactions.

Photoelectric absorption

An interaction where an x-ray photon is completely absorbed by an inner-shell electron, which is then ejected as a photoelectron; accounts for about $27\%$ of dental x-ray interactions.

Density

The overall darkness or blackness of a radiographic image, influenced by mA, kVp, exposure time, and subject thickness.

Contrast

How sharply dark and light areas are differentiated on an image; controlled primarily by kVp.

Inverse Square Law

The principle stating that the intensity of radiation is inversely proportional to the square of the distance from the source.

Direct effect (Radiation Biology)

Damage that occurs when biologic molecules absorb energy from ionizing radiation directly to form unstable free radicals; accounts for one-third of biologic effects.

Indirect effect (Radiation Biology)

Damage resulting from the radiolysis of water, where free radicals like hydroxyl ($OH^\bullet$) are formed and subsequently damage DNA; accounts for two-thirds of biologic damage.

Deterministic effects

Radiation effects characterized by a threshold dose, where the severity of the injury (e.g., cell death, cataracts) depends on the dose received.

Stochastic effects

Sublethal radiation effects (e.g., cancer, genetic mutations) that do not have a threshold; the probability of occurrence depends on the dose, but severity does not.

Absorbed Dose

The amount of energy deposited by ionizing radiation per unit mass of tissue, measured in Gray ($Gy$).

Equivalent Dose ($H_T$)

The absorbed dose adjusted for the biological effectiveness of the radiation type, measured in Sieverts ($Sv$).

Effective Dose ($E$)

A calculated value accounting for the varying radiosensitivity of different tissues, used to assess total cancer risk; measured in Sieverts ($Sv$).

ALARA

The principle of radiation protection standing for 'As Low As Reasonably Achievable,' involving the optimization of exposure.