ASNT NDT III RT key terms

The thickness of a specified material that reduces the intensity of a radiation beam to one half of its original value under narrow-beam conditions. It is a common measure of beam penetrating power and radiation quality.

The fraction of radiation intensity removed per unit path length as a beam passes through a material. It depends on photon energy and material density and is used to calculate transmitted intensity.

The linear attenuation coefficient divided by material density, giving attenuation per unit mass thickness. It allows comparison of materials independent of density and is tabulated versus photon energy.

The shift of a polychromatic X-ray beam toward higher average energy as lower-energy photons are preferentially absorbed in the material. It increases effective penetration and can cause nonuniform exposure through thick sections.

A description of the penetrating ability of a radiation beam, commonly expressed by half-value layer or effective energy. Higher quality means greater penetration and typically higher kilovoltage or gamma energy.

The physical area on the anode of an X-ray tube where X-rays are generated. A smaller focal spot produces sharper images but limits tube current because of heat concentration.

Blurring of a radiographic image caused by the finite size of the radiation source, the source-to-object distance, and the object-to-detector distance. It is reduced by smaller sources or greater source-to-object distance.

The distance from the radiation source to the image receptor or film. Increasing this distance reduces geometric unsharpness and increases exposure time needed for a given technique.

The principle that radiation intensity from a point source decreases in proportion to the square of the distance from the source. Doubling distance reduces intensity to one quarter.

The peak voltage applied across an X-ray tube, which controls the energy spectrum and penetrating power of the emitted X-rays. Higher kilovoltage generally increases penetration and reduces exposure time.

The product of radiation intensity and time that reaches the image receptor, controlling the resulting film density or digital signal level. It is adjusted by tube current, time, distance, and source activity.

A measure of the darkness of a processed radiograph, defined as the logarithm of the ratio of incident to transmitted light intensity. Acceptable ranges are usually specified by the applicable code or standard.

A plot of film density versus the logarithm of relative exposure for a given film and processing condition. It describes film speed, contrast, and latitude and is used to select exposure parameters.

The slope of the characteristic curve at a given density, indicating how much density change results from a given change in exposure. Higher contrast makes small thickness or density differences more visible.

The relative difference in radiation intensity transmitted through different regions of a part because of differences in thickness, density, or composition. It is influenced by beam quality and scatter.

A device, such as a wire or hole-type penetrameter, placed on or near the part to demonstrate the achieved radiographic sensitivity. It verifies that the technique can reveal specified discontinuities.

A measure of the smallest discontinuity or feature detectable in a radiograph, often expressed as the smallest wire or hole visible in the IQI. Better sensitivity means smaller features are detectable.

The ability of an imaging system to distinguish closely spaced features as separate in the image. In film it relates to grain and geometry; in digital systems it depends on pixel size and detector design.

Radiation that has been deflected or changed in energy within the part, fixture, or surroundings and reaches the detector from unintended directions. It reduces contrast and is controlled with lead screens, masks, and collimation.

Restricting the radiation beam to the area of interest using absorbers such as lead diaphragms or cones. It reduces scatter, limits radiation dose, and improves image contrast.

A thin lead foil placed adjacent to film to absorb scattered radiation and to emit secondary electrons that enhance film exposure. Front and back screens improve contrast and reduce exposure time.

A material, often a fluorescent phosphor or metal foil, placed next to film to convert some radiation into light or electrons. It reduces required exposure but may reduce image sharpness.

An imaging method in which a radiation image is converted to a visible or electronic display and observed as it is produced. It is used for dynamic inspection and motion studies rather than static film.

A method in which transmitted radiation is captured by an electronic detector and converted into digital image data for display, storage, and analysis. It offers adjustable contrast and rapid image access.

A digital method using a photostimulable phosphor imaging plate that stores a latent image, later read by a laser scanner. The plate can be reused after erasure.

A radiographic technique in which X-rays produce a visible image on a fluorescent screen or electronic imager for direct viewing. It is commonly used for real-time inspection of internal features.

An instrument that measures the optical density of a processed radiograph by comparing light transmitted through the film with a reference. It is used to verify compliance with density requirements.

A written document specifying exposure parameters, source, distance, screens, IQI, and processing for a given part or family of parts. It ensures repeatable and code-compliant radiography.

The difference in image density or signal between adjacent regions of a radiograph. Adequate contrast is needed to detect discontinuities and depends on subject contrast and image system response.

Demonstration by documented test that a written radiographic procedure produces acceptable results for its intended application. It typically includes demonstration of sensitivity and compliance with a code.

Formal recognition that an individual has met specified training, experience, and examination requirements for a method and level. Certification supports competence and is often required by codes and contracts.

A designated person responsible for implementing and supervising a radiation protection program, including dose monitoring, training, and compliance with regulations. The role may be assigned under applicable regulations.

The principle of keeping radiation exposure as low as reasonably achievable, considering economic and social factors. It guides work practices, shielding, and planning of radiographic operations.

A device worn or carried to measure an individual's accumulated radiation dose over a period. It is used to monitor occupational exposure and demonstrate compliance with dose limits.

The amount of radiation energy deposited per unit mass of material, typically expressed in gray or rad. It is a fundamental quantity for assessing radiation effects on matter and tissue.

A general term for the rate at which radiation intensity is reduced per unit thickness or mass as it passes through matter. It is the basis for exposure calculations and shielding design.

The effective dimensions of the radiation-emitting area of an X-ray tube or gamma source. It directly influences geometric unsharpness and the smallest detail resolvable in a radiograph.

Radiation absorption that occurs within the X-ray tube and its housing before the beam exits. It removes low-energy photons and affects beam quality and minimum permissible kilovoltage.