MT: Symbol for the magnetic particle method of nondestructive testing/inspection.
MULTIAXIAL STRESSES: Any stress state in which two or three principal stresses are not zero.
MULTI-DIRECTIONAL MAGNETIZATION: Two separate fields, having different directions, cannot exist in a part at
the same time. But two or more fields in different directions can be imposed upon a part sequentially in rapid
succession. When this is done magnetic particle indications are formed when discontinuities are located favorably with
respect to the directions of each of the fields, and will persist as long as the rapid alternations of field direction
continue. This, in effect, does constitute two or more fields in different directions at the same time, and enables the
detection of defect oriented in any direction in one operation.
MULTIPLE REFLECTIONS (UT): Successive echoes of ultrasonic energy between two surfaces.
NANOMETER (PT): A unit of length equal to one billionth of a meter, or 10-9 meter. The Nanometer has replaced
the angstrom unit as a measurement of short wave length, electromagnetic radiation where 1 nm = 10 angstroms.
NANOSECOND: (10-9) one billionth of a second.
NARROW-BANDED (UT): Having a relatively narrow bandwidth; opposite of broad-banded; see TUNED.
NEAR FIELD (UT): The region of the ultrasonic beam adjacent to the search unit, having complex beam profiles; also
known as the Fresnel zone. The length of the near field extends from the face of the search unit to the point at which
the far field begins and is given by the equation: L0 = D2f /4v
L0 = near field length - inches.
D = the major dimensions of the search unit element - inches.
For circles, D = the diameter. For rectangles or squares, D = diagonal.
f = ultrasonic frequency - hertz.
v = ultrasonic velocity - inches per second.
NEIGHBORHOOD EFFECT (RT): The name given to various effects arising from the diffusion of developer which has
become locally exhausted or loaded with oxidation products by its action on a heavily exposed region of an emulsion.
Typical examples are developer streaks and abnormal density variations near the edges of regions of high density.
NET DENSITY (RT): Total film density less the base plus fog density.
NETWORK STRUCTURE: A structure in which one constituent occurs primarily at the grain boundaries, thus
partially or completely enveloping the grains of the other constituents.
NEUTRON: An uncharged elementary particle with a mass nearly equal to that of the proton. The isolated neutron is
unstable and decays with a half-life of about 13 minutes into an electron, proton, and neutrino. Neutrons sustain the
fission chain reaction in a nuclear reactor. Neutron radiograph is a technique in which neutrons are used as a
penetrating radiation to produce a radiograph.