ABSOLUTE (ET): Refers to measurements made without a direct reference in contrast to differential measurements.
Absolute measurements are affected by any change in electromagnetic properties; differential measurements are
affected only by differences between the test area and a comparative standard.
ABSOLUTE PROBE: A probe containing a coil that responds to all electromagnetic properties of the test part.
ABSOLUTE SIGNAL: The value of the amplitude of a signal without consideration of its relative phase, frequency or
ABSORBED DOSE: The energy imparted by ionizing radiation per unit mass of irradiated material. The units of
absorbed dose are the rad and the gray (Gy).
ABSORPTION: The process whereby the particles or quanta (see PHOTON) in a beam of radiation are reduced in
number or energy as they pass through some medium. The particles lose energy by interaction with either the nucleus
(core) or electrons (shell) of the atoms of the medium.
ABSORPTION COEFFICIENT (RT): A fraction expressing the decrease in the intensity of a beam of radiation per unit
thickness (linear absorption coefficient), or per atom (atomic absorption coefficient of the medium through which the
radiation is passing).
ABSORPTION COEFFICIENT, LINEAR (UT): The fractional decrease in transmitted intensity per unit of absorber
material thickness. It is designated by the symbol (µ) and is expressed in units of cm-1.
ABSORPTION (PT): The process of one material (liquid, solid, or gas) merging with a second material by penetration
into the particles of the second material ... as opposed to adsorption where the material coats and is retained on the
surface of the particles of the second material.
ABSORPTION (RT): The process whereby the particles or quanta (see PHOTON) in a beam of radiation are reduced in
number or energy as they are passed through some medium. The particles lose energy by interaction with either the
nucleus (core) or electron (shell) of the atoms of the medium.
ADSORPTION (PT): The process of one material (liquid, solid, or gas) merging with a second material by coating and
being retained on the surface of the particles (and interstices) of the second material ... as opposed to absorption where
the material penetrates into the particles of the second material.
AC (ALTERNATING CURRENT): Electric current that reverses its direction of flow at regular intervals.
ACCELERATOR: A device that accelerates charged atomic particles to high energies. An X-ray machine or a betatron
is an accelerator.
ACCEPTANCE NUMBER: The term used to designate the allowable number of defects in a statistical quality control
ACID EMBRITTLEMENT: A form of hydrogen embrittlement that may be induced in some metals by acid treatment.
ACOUSTIC IMPEDANCE (UT): A material property, which determines the product of the velocity of sound in a
material and the density of the material used in determining the reflection characteristics of interfaces.