Glossary of Terms for Radiographic Testing
Absorb dose:
The amount of energy imparted by ionizing radiation per unit mass of irradiated matter. Indicated by "rad"; 1 rad = 0.01j/kg. SI units is "gray"; 1 gray = 1 J/kg.
Absorb dose rate:
the absorbed dose per unit of time; rad/s or as SI unit gray/s.
Absorption:
The process whereby the incident particles or photons of radiation are reduced in a number or energy as they pass through matter, i.e. the energy of the radiation beam is attenuated. Note that the total attenuation is the sum of the components due to photoelectric absorption, Rayleigh scattering, Compton scattering and pair production.
Accelerating potential:
The difference in electric potential between the cathode and anode in an X-ray tube through which a charged particle is accelerated, usually spezified in units of kV or MV.
Activity:
The number of nuclear transitions occurring in a given quantity of radioactive material per unit of time. For example one disintegration/second is a becquerel (Bq), which has replaced curie (Ci) as the standard unit of activity.
Acute radiation syndrom:
The immediate effects of a short term, whole body overexposure of a person to ionizing radiation. These effects include nausea and vomiting, malaise, increase temerature, and blood change.
Ageing fog:
The increase in optical density on an unexposed film, measured after processing, due to long-term storage.
Alpha particle:
The nuclei of a helium atom (with two neutrons and two protons each) that are discharged by radioactive decay of many heavy elements, such as uranium-238 and plutonium-239.
Anode:
The positive electrode of an X-ray tube. In an X-ray tube, the anode carries the target.
Anode current:
The electrons passing from the cathode to the anode in an X-ray tube. There is a small loss incurred by the back scatted fraction.
Artefact (false indication):
A spurious indication on a radiograph arising e.g. from faults in the manufacturing, handling, exposing or processing of a film.
Attenuation:
The reduction in intensity of a beam of X- or gamma radiation during its passage through matter caused by absorption and scattering.
Attenuation coefficient µ:
The relationship between the intensity (I0) of a radiation incident on one side of an absorber and the transmitted intensity (I) for an absorber thickness (t) as expressed by I0 10 exp (-µt).
Average gradient:
The slope of a line drawn between two specified points on the sensitometric curve.
Back scatter/back scattered radiation:
Radiation which is scattered at an angle of more than 90° in relation to the direction of the incident beam.
Beam angle:
The angle between the central axis of the radiation beam and the plane of the film.
Becquerel:
The SI unit of activity equal to one disintegration per second. [37 billion (3.7x1010) becquerels = 1 curie (Ci)].
Betatron:
A machine in which electrons are accelerated in a circular orbit before being deflected onto a target to produce high energy X-rays. This type of equipment usually operates at energies between 10 and 31 MEV.
Blocking medium:
A absorptive material surrounding specimens or covering their sections used to reduce the effect of scattered radiation on the film or on the image detector.
Build-up factor:
The ratio of the intensity of the total radiation reaching a point, to the intensity of the primary radiation reaching the same point.
Calibrated density step wedge:
A piece of film having a series of different optical densities which have been calibrated to be used as reference densities.
Cassette:
A rigid or flexible light-tight container for holding radiographic recording media (film or paper) with or without intensifying screens, during exposure.
Cathode:
The negative electrode of an X-ray tube.
Characteristic curve:
A curve (of a film) showing the relationship between the common logarithm of exposure, log K, and the optical density, D. Also called the D-log E curve or the H and D curve.
Clearing time:
The time needed for the first stage of fixing of a film, during which the cloudiness disappears.
Collimation:
The limiting of a beam of radiation to a form of required dimensions, by the use of diaphragms made of absorbing material.
Collimator:
A device made from radiation absorbent material such as lead or tungsten, designed to limit and define the direction and angular divergence of the radiation beam.
Compton scatter:
A form of scattering caused by a photon of X- or gamma radiation interacting with an electron and suffering a reduction of energy, the scattered radiation being emitted at an angle to the incident direction. Since the ejected electron has a short range in most materials, it is not considered part of the scattered radiation. For radiation in the energy range 100 keV to 10 MeV, it is the main factor contributing to radiation attenuation.
Computerized tomography (CT):
A procedure by which an image of the detail in a chosen plane, perpendicular to the axis of the specimen, is computed from a large number of X-ray absorption measurements made from many directions perpendicular to the axis. This is computerized axial tomography and does not apply to other means of performing tomography.
Constant potential circuit:
An electronic configuration which is designed to apply and maintain a substantially constant potential within an X-ray tube.
Continuous spectrum:
The range of wavelengths or quantum energies generated by an X-ray set.
Contrast:
See "Image contrast", "Radiation contrast", "Object contrast" and "Visual contrast".
Contrast medium:
Any suitable substance, solid or liquid, applied to a material being radiographed to enhance its radiation contrast in total or in part.
Contrast sensitivity (thickness sensitivity):
The smallest thickness change in specimen which produces a discemible change in optical density on a:, radiogragphic (or radioscopicl image, usually expressed as a perceatageof the total specimen thickness.'
Curie (Ci):
The unit used to describe the intensity of radioactivity in a sample of material. The curie is equal to 37 billion (3.7 x 1010) disintegrations per second, which is approximately the activity of 1 gram of radium. The Becquerel (Bq) has replaced the Ci in the SI system. The Becquerel (Bq) is 1 disintegration per second.
Decay curve:
Tftw,activity of a radiois setope;,,plotted a alInst time, usually As a Idg/lInoar. jelationship.
Densitometer:
A device for the measurement, of the optical density of a radiographic film or reflective density of a photographic print.
Development (of a film or paper):
chemical or physical process which converts a latent image into a visible image.
Diffraction mottle:
A superimposed pattern on a radiographicimtoe due to diffraction of the incident radiation by the material structure.
Dose rate rreter:
An instrument for the measurement of X- or gamma radiation dose-rate.
Dosemeter (dosimeter):
An instrument for measuring the accumulated dose of X- or gamma radiation.
Dual focus tube:
An X-ray tube with two different sizes of focus.
Dublex wire image quality indicator:
An image quality indicator specifically designed to assess the overall unsharpness of a radiographic image and composed of a series of pairs of wire elements made of high density metal.
Edge-blocking material:
Material applied around a specimen or in cavities to obtain a more uniform absorption, to reduce extraneous scattered radiation, and to prevent local over-exposure, e.g, fine lead shot (see also "Blocking medium").
Equalizing filter (beam flattener):
A device used to equalize the intensity across the primary X-ray beam in megavoltage radiography and so extend the useful field size.
Equivalent X-ray voltage:
The voltage of a X-ray tube which produces a radiograph most nearly equivalent to a gamma radiograph taken with a particular gamma-ray source.
Exposure:
The process whereby radiation is recorded on an imaging system.
Exposure calculator:
A device (for example a slide rule) which may be used to determine the exposure time required.
Exposure chart:
A chart indicating the time for radiographic exposures for different thicknesses of a specified material and for a given quality of a beam radiation,
Exposure latitude:
The range of exposures corresponding to the useful optical density range of the emulsion.
Exposure time:
Duration of the process of exposing a recording medium to radiation.
Film base:
The support material on which the photosensitive emulsion is coated.
Film gradient (G):
The slope of the characteristic curve of a film at a specified optical density D.
Film illuminator (viewing screen:
(viewing screen) Equipment containing a source of light and a translucent screen used for viewing radiographs.
Film processing:
The operations necessary to transform the latent image on the film into a permanent, visible image, consisting normally of developing, fixing, washing and drying a film.
Film system speed:
A quantitative measure of the response of a film system to radiation, energy, for specific exposure. conditions.
Filter:
Uniform layer of material, u !sual higher atomic number than the spectmen, placed between 1hp. radiation source and the film or e purpose of Preferentially absorbing::. the -softer radiations.
Fixing:
The chemical removal of silver halides from a film emulsion after development.
Flaw sensitivity:
The minimum flaw size detectable under specified test conditions.
Fluorescent intensifying, screen:
A screen consisting of a coating of phosphors which fluoresces when exposed to X- or gamma radiation.
Fluorometallic intensifying screen:
A screen consisting of a metallic foil (usually lead) coated with a material that fluoresces when exposed to X- or gamma radiation.
Fluoroscopy:
The production of a visible image on a fluorescent screen by X-rays and for direct viewing of the screen.
Focal spot size:
The dimension across the focal spot of an X-ray tube, measured parallel to the plane of the film or the fluorescent screen.
Focalspot:
The X-ray emitting area on the anode of the X-ray tube, as seen from the measuring device.
Focus-to-film distance (ffd):
The shortest distance from the focus of an X-ray tube to a film set up for a radiographic exposure.
Fog density:
A general term used to denote the optical density of a processed film caused by anything other than the direct action of image - forming radiation. It can be aging fog, chemical fog, dichroic fog, exposure fog or inherent fog.
Gamma Radiation:
High-energy, short wavelength electromagnetic radiation emitted from the nucleus of an atom. Gamma rays are very penetrating and are shielded by dense materials such as lead. Gamma rays are similar to X rays.
Gamma radiography:
Radiography using a gamma-ray source.
Gamma rays:
Electromagnetic ionizing radiation, emitted by specific radioactive materials.
Gamma-ray source:
Radioactive material sealed into a metal capsule.
Gamma-ray source container:
A container made of dense material and having a wall thickness sufficient to produce a very great reduction in the intensity of the radiation emitted by the source, so as to make it safe to handle.
Geometric unsharpness:
Unsharpness of a radiographic image arising from the finite size of the source of radiation. Its magnitude also depends on the distances of sourceto-object and object-to-film. Also called geometric blurring or penumbra.
Graininess:
The visual appearance of granularity.
Granularity:
The stochastic density fluctuations in the radiograph superimposed on the object image.
gray (Gy):
The SI (International System of Units) unit of radiation dose. The unit is named for the British physician L. Harold Gray (1905-1965), an authority on the use of radiation in the treatment of cancer.
Half life:
The time in which half the atoms of a radioactive substance will have disintegrated, leaving half the original amount. Half the residue will disintegrate in another equal period of time. The half-life values for radioisotopes vary widely.
Half value thickness (HVT):
The thickness of specified material which, when introduced into the beam of X- or gamma radiation, reduces its intensity by a half.
Illuminator:
An intense white light source for viewing radiographs.
Image contrast:
Image definition:
A qualitative term used to define sharpness of delineation of image detail in a radiograph.
Image enhancement:
Any process which increases the image definition by improving contrast and/or definition or reducing noise. When accomplished by computer programmes, it is referred to as digital image processing.
Image intensifier:
An electronic device that provides a brighter image than that produced by the unaided action of an X-ray beam on a flourescent screen.
Image quality:
That characteristic of a radiographic image defined by the degree of detail it shows.
Image quality indicator (IQI):
A device used to establish a measure of the radiographic image quality. An IQI is commonly made using wires or steps with holes.
Image quality value, IQI sensitivity:
A quantitative indication of the image quality required or achieved.
Incident beam axis:
The axis of the beam of X-radiation defined by the focal spot and the tube window.
Industrial radiology:
The use of X-rays, gamma rays, neutrons and other penetrating radiation for nondestructive testing.
Inherent filtration:
The reduction of softer radiation (lower energy) of a radiation beam by the parts of the X-ray tube, set up or source incapsulation components, through which the primary beam will pass.
Inherent unsharpness:
The blurring of a radiographic image caused by scattered secondary radiation in the imaging medium such as the photographic emulsion whereby these electrons render the silver halide grains developable.
Intensifying factor:
The ratio of the exposure time without intensifying screens, to that when screens are used, to obtain the same optical density.
Intensifying screen:
A material used in radiographic production to converts a part of the ionising radiation into light or electrons and that, when in contact with a recording medium during exposure, improves the quality of the radiograph, or reduces the exposure time required to produce a radiograph or both. Also see "Fluorometallic intensifying screen", or "Fluorescent intensifying screen".
Kerma:
An alternative term used for absorbed dose. Kerma is usually used to describe the transfer of energy from photons to electrons.
Latent image:
A condition produced in an image receptor by radiation and capable of being converted into a visible image by film processing.
Linear electron accelerator (LINAC):
A device for accelerating charged particles in a straight line, either by a steady electric field or by a radio-frequency electric field.
Masking:
The application of material which limits the area of irradiation of an object to the region undergoing radiographic examination to minimse image deterioration due to scatter radiation.
Metal screen:
A screen consisting of dense metal (usually lead) that both filters radiation and intensifies an image by emiting electrons when exposed to X- or gamma rays.
Microfocus radiography:
Radiography using an X-ray tube having a small effective focus-size of less than 0.1mm in size. Used for geometric enlargement of the image by projection.
Modulation transfer function (MTF):
The ratio of the image amplitude to the object amplitude as a function of sinusoidal frequency variation in the object.
Movement unsharpness:
Blurring of a radiographic or radioscopic image as a result of relatitve movement of the radiation source, object or, radiation detector.
Neutron:
An neutral hadron that is stable in the atomic nucleus but decays into a proton, an electron and an antineutrino with a half-life of 12 minutes outside of the nucleus. In the nucleus it has a rest mass slightly greater than the proton and a neutral charge.
Object contrast:
The relative difference of radiation transmitted between two regions of an irradiated object.
Object-to-film distance:
The distance between the radiation side of a test object and the film used to radiograph the object as measured along the central axis of the radiation beam.
Panoramic exposure:
A radiographic set-up whereby several objects are exposed simultaneously, or the full circumference of a cylindrical specimen is exposed by the onmidirectional characteristics of the radiation source.
Penetrameter:
Pressure mark:
A blemish on a radiograph, which may be light or dark in appearance, depending on circumstances, and caused by local pressure to the film.
Primary radiation:
Radiation which travels along a straight line, without scatter, from the source to the detector.
Projective magnification:
The degree of image size enlargement.
Projective magnification technique Quality (of a beam of radiation):
Also called Projection Microfocus radiography. A method of radiography or radioscopy that provides an enlargement of the image by the use of a distance between the specimen and imaging system. (see "Microfocus radiography").
rad (rd):
An old unit of absorbed radiation dose. One rad is equal to a dose of 0.01 joule of energy per kilogram of mass (J/kg); one rad equals 0.01 gray or 10 milligrays. "Rad" is an acronym for "radiation absorbed dose."
Quality of a beam of radiation:
The penetrating ability of a specified form of radiation, usually measured as a half-value thickness of a specified material.
Radiation contrast:
Differences in radiation intensity due to variation in radiation opacity within an irradiated object.
Radiation source:
Equipment used for generating X-rays or gamma rays or other penetrating radiation sources(e.g. protons, neutrons, Beta rays).
Radiograph:
A visible image after processing produced by a beam of penetrating radiation on a radiographic film or paper.
Radiographic film:
An image storage medium consisting of a transparent base, usually coated on both sides with a radiation sensitive emulsion.
Radiography:
The production of permanent visual image using penetrating radiation through the material tested.
Radioscopy:
The electronic production of a visual image by ionising radiation on a radiation detector and displayed on a monitor or similar screen.
Radioisotope:
An unstable isotope of an element that decays by emitting particles or gamma radiation or X-radiation.
Rod anode tube:
Uni-polar tubes with a long hollow anode in which the target is situated at the extremity of a tubular anode. These tubes generally produce a panoramic beam of radiation.
Scattered Radiation:
Particulate or EM radiation that has undergone a change in direction with or without a change in energy, during its passage through intervening matter.
Screen type film:
Radiographic fiIm designed to be used with fluorescent or lead intensifying screens.
SI units:
Abbreviation for Système International d'Unités. The international system of units derived from the m.k.s. units.
Sievert:
The SI unit of absorbed dose equivalent (1 Joule/Kilogram or 100 rems).
Source holder:
A container for a gamma ray source (sealed source).
Source size:
An indication of the radioactive intensity of a radioactive mass typically in units of Bequerels (formerly in Curies).
Source-to-film distance (sfd):
The distance between the source of radiation and the film along the path of the beam of radiation.
Spatial resolution:
The ability to form separable images of close objects.
Specific activity:
The number of atoms of a radioactive substance that disintigrate per unt time per unit mass of a radioisotope.
Step wedge:
An object with specified thickness steps used to obtain a radiograph of discrete densitiy values.
Stereo radiography:
The production of two radiographs made using a source shift exactluy parallel to the film plane.
Target:
A high melting point metal on the end of the anode of an X-ray tube on which the electron beam impinges and from which the primary beam of X-rays is emitted
Tube diaphragm:
A device, normally fixed to a tube shield in front of the tube window, used to reduce scatter by limiting the extent of the emergent X-ray beam.
Tube head:
One of the three main parts of an X-ray installation. The tube head contains the tube in its shield, the other two include the transformer and control panel.
Tube shield:
The metal container that supports the X-ray tube and hold the coolant and electrical insulation fluid. It also provides a means of reducing the leakage radiation.
Tube shutter:
A device used on an X-ray tube, used to regulate the X-ray beam, usually made of lead and remotely operated.
Tube voltage:
The potential difference between the anode and the cathode of an X-ray tube, usually measured in kilovolts (kV).
Tube window:
An area of relative transparency to X-rays in the X-ray tube through which the radiation is emitted.
Unsealed source:
Any radioactive material not encapsulated for safe handling.
Unsharpness:
A quantified value of image blurring. It is the total of "geometric unsharpness", "inherent unsharpness" and "movement unsharpness",
Useful density range:
The practical range of optical density on a radiograph. Maximum density is determined by the film illuminator and the minimum by the loss in flaw sensitivity.
Vacuum cassette:
A light-tight container using a vacuum to hold a radiographic recording media, film and screens, in intimate contact during radiographic exposure.
Viewing mask:
A device used with a radiographic illuminator used to exclude excessive transmitted light or to prevent light from passing the edges of the radiograph.
Visual contrast:
A density difference perceived visually between two adjacent areas when viewing a radiograph.
X-ray film:
X-ray tube:
A device for generating X-rays by accelerating electrons from a filament to strike a metal target (anode).
X-rays:
Electromagnetic radiation (photon), of shorter wavelength than ultraviolet radiation. Produced by bombardment of atoms by high-quntum-energy particles. Radiation wavelength is from 10-11 to 10-9 m.
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