T.O. 33B-1-1Glossary 57MT: 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 atthe same time. But two or more fields in different directions can be imposed upon a part sequentially in rapidsuccession. When this is done magnetic particle indications are formed when discontinuities are located favorably withrespect to the directions of each of the fields, and will persist as long as the rapid alternations of field directioncontinue. This, in effect, does constitute two or more fields in different directions at the same time, and enables thedetection of defect oriented in any direction in one operation.MULTIPLE REFLECTIONS (UT): Successive echoes of ultrasonic energy between two surfaces.NNANOMETER (PT): A unit of length equal to one billionth of a meter, or 10-9 meter. The Nanometer has replacedthe 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; alsoknown as the Fresnel zone. The length of the near field extends from the face of the search unit to the point at whichthe far field begins and is given by the equation: L0 = D2f /4vwhere: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 hasbecome 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, thuspartially 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 isunstable and decays with a half-life of about 13 minutes into an electron, proton, and neutrino. Neutrons sustain thefission chain reaction in a nuclear reactor. Neutron radiograph is a technique in which neutrons are used as apenetrating radiation to produce a radiograph.
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