REFERENCE BLOCKS: A block or series of blocks of material containing artificial or actual discontinuities of one or
more reflecting areas at one or more distances from the test surface, which are used for reference in defining the size
and distance of defective areas in materials.
REFERENCE NUMBER: A mathematical value established to summarize the combined effects of conductivity,
magnetic permeability, test frequency, coil radius and thickness for use in impedance diagrams.
REFERENCE RADIOGRAPHS: A group of radiographs containing images of discontinuities. These can be used as
comparison standards for acceptability of materials.
REFERENCE STANDARD: A piece of material, part, or piece from a part, containing an artificial discontinuity of
known size; provides a means of producing a reflection of known characteristics; used to establish a measurement scale.
Also, a known size discontinuity used to produce a reflection of known characteristics. References are constructed for
thickness measurement, conductivity measurement or flaw detection.
REFLECTION (UT): An indication that has arisen as a result of an incident sound beam being reflected at the
boundary of two materials of dissimilar acoustic impedance.
REFLECTION DENSITY (RT): The common logarithm of the ratio of the brightness of a non-absorbing perfect
diffuser to that of the sample, both being illuminated at an angle of 45 degrees to the surface, the direction of
measurement being normal to the surface.
REFLECTOGRAM: A picture of recording of the indications presented on the cathode ray tube of the ultrasonic
REFLECTOGRAPH: A recording or chart made of either the signals transmitted through a part or reflected back from
defects within a part, or both.
REFLECTOR (UT): An interface at which an ultrasonic beam reflects.
REFRACTED BEAM (UT): The beam that occurs in the second medium when an ultrasonic beam passes obliquely
from one medium to another when each medium has different sound velocities.
REFRACTION (UT): Change in direction of an ultrasonic beam as it passes obliquely through the interface between
two materials with different acoustic velocity; see SNELLS LAW.
REFRACTIVE INDEX (UT): The ratio of the velocity of a wave in one medium to the velocity of the wave in a second
medium is the refractive index of the second medium with respect to the first. It is a measure of the amount a wave will
be refracted when it enters the second medium after leaving the first.
A material of very high melting point with properties that make it suitable for such uses as furnace linings
and kiln construction.
The quality of resisting heat.
A heat-resistant alloy.
An alloy having an extremely high melting point. See REFRACTORY METAL.
An alloy difficult to work at elevated temperatures.