- A relative term denoting a restricted range of frequency response.
- Natural Frequency
- The frequency at which an object will vibrate
freely when set in motion.
- cosmogenic (extraterrestrial) and terrestrial radiation with an activity
range that is usually around 5-10 micro roentgens per hour, The term "naturally
occurring" needs to be differentiated from "background radiation,"
which now includes the impact of the cumulative deposition from stratospheric
fallout and nuclear accidents such as Chernobyl. In some contaminated areas,
such accumulations of long-lived artificially produced radionuclides exceed
natural background radiation levels.
- NDE -
Acronym for Nondestructive Evaluation
Acronym for Nondestructive Testing.
- NDT Methods
- A process used to test an object for flaws and
other defects that does not harm the object.
Field - The distance immediately in front of the transducer in which
the ultrasonic beam exhibits complex and changing wavefronts. Also called
the Fresnel Field or Fresnel Zone.
- The natural logarithm of a ratio of two amplitudes (equal to 8.686 dB) used
as a measure of attenuation. Power ratios are expressed as one-half the natural
- Neutron -
One of the basic particles which make up an atom
and is about the same size as a proton but has no electrical charge.
- Neutron Activation
- The process of bombarding a material with neutrons.
- A source that emits neutrons, e.g. a poloniumberyllium source, sometimes
used in radiography where background fields are high, e.g. in a reactor room.
Inverse Square Law - The intensity of the influence
at any given radius (r) is the source strength divided by the area of the
- An elevated-temperature process (but lower than carburizing or carbonitiding)
by which a ferrous metal absorbs nitrogen atoms into the surface when exposed
to a high-nitrogen environment. Nitrogen atoms actually diffuse, or flow,
into the metal to form a high-nitrogen surface layer.
Points - In angle beam testing, the location of reflections at opposite
surfaces as a wave progresses along a test object.
- A point in a standing wave where a given characteristic of the wave field
has zero amplitude.
- Any undesired signal that obscures the signal of interest.
- It might be electrical noise or a signal from specimen dimensional or property
- Made with liquids other than water.
Evaluation (NDE) - The use of non-invasive techniques to determine
the integrity of a material, component or structure, or to quantitatively
measure some characteristic of an object. (Making quantitative measurements
is what distinguishes NDE from NDT.)
Testing (NDT) - Testing to detect defects in materials using techniques
that do not damage or destroy the items being tested.
- Describing a metal that is less than 50% iron, such as aluminum, copper,
magnesium, and zinc and their alloys.
Indication - An indication that has no relation to a significant
- Normal Beam
Inspection - Pulse-echo ultrasonic measurements
can determine the location of a discontinuity in a part or structure
Incidence - A condition in which the axis of the ultrasonic beam
is perpendicular to the entry surface of the test object.
- A condition where the angle of incidence is zero.
- Normal Incidence
Shear Wave Transducers - A transducer that allows
shear waves directly into a test piece without the use of an angle beam wedge.
- Nuclear Fission
- A process which involves
the splitting of nuclei with the accompanying release of energy.
- Nuclear Fusion
- A process whereby
several small nuclei are combined to make a larger one whose mass is slightly
smaller than the sum of the small ones.
- Nuclear Radiation
- Radiation emitted
from an unstable atomic nucleus.
- A reaction involving an atom's nucleus, such as fission, neutron capture,
radioactive decay, or fusion, as distinct from a chemical reaction, which
is limited to changes in the electron structure surrounding the nucleus.
- Nuclear Reactors
- Devices that control fission reactions producing
new substances from the fission product and energy.
- A nuclear particle-either a proton or neutron or both collectively.
- Nucleus -
center of an atom containing protons and neutrons.
- Any species of atom that exists for a measurable length of time. A nuclide
can be distinguished by its atomic weight, atomic number, and energy state.
The term is used synonymously with isotope. A radionuclide is a radioactive