DECAY (RT): Spontaneous change of a nucleus with emission of a particle or a photon. For a definite quality of a
nuclide, the rate of decay is usually expressed in terms of half-life.
DECAY CURVE (RT): A graph showing radioactive strength in curies as a function of time for an isotope. Such
curves are used in radiography to determine the compensation or correction for exposure time in selecting exposure
DECIBEL: Logarithmic expression of a ratio of two amplitudes; abbreviation is dB. dB -20 log10 (A2/Al), where Al
and A2 are amplitudes.
DECONTAMINATION (RT): The removal of radioactive contaminants from surfaces by cleaning and washing with
DECONTAMINATION FACTOR (RT): The ratio of the amount of radioactive contaminant initially present to the
amount remaining after a suitable processing step has been completed. A factor referring to the reduction of the gross
DEEP-DOSE EQUIVALENT: Applies to whole-body exposure, is the dose equivalent at a tissue depth of 1 cm (1000
DEEP ETCHING: Severe etching of a metallic surface for examination at a magnification of ten diameters or less to
reveal gross features such as segregation, cracks, porosity or grain flow.
DEFECT: A discontinuity that interferes with the usefulness of a part. A fault in any material or part detrimental to its
serviceability. Note that all cracks, seams, laps, etc. are not necessarily defects as they may not affect serviceability of
the part in which they exist.
DEFECT DETECTION SENSITIVITY (RT): See sensitivity, defect.
DEFECT ORIENTATION (PT, MT): The position of the defect in relation to the inspection surface and the magnetic
or penetrant indication.
DEFECT REFLECTION (UT): The oscilloscope presentation of the energy returned by a rejectable flaw in the
DEFECT RESOLUTION: A property of a test system which enables the separation of signals due to defects in the test
specimen that are located in close proximity to each other.
DEFINITION, RADIOGRAPHIC (RT): Measure of sharpness in outline in the radiographic image of an object.
Radiographic definition is a function of the types of screens, exposure geometry, radiation energy, and the film
DEFINITION (RT): A general and qualitative term that refers to the degree of distinctness of image details in a
radiograph, photographic reproduction, or viewing-screen image.
DEGREASING FLUID: Solvents or cleaners employed to remove oil and grease from the surface of components before
the penetrant liquid is applied.
DELAY (UT): See SWEEP DELAY.
DELAY COLUMN (UT): See WATER DELAY COLUMN.
DELAY LINE (UT): Material (liquid or solid) placed in front of the search unit to cause a time delay between the
initial pulse and front surface signal.