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  • IACS(International Annealed Copper Standard) - Conductivity as a percentage of pure copper.
  • Icicles (Burn Through) - A coalescence of meal beyond the root of the weld.
  • Imaging - A process to produce an image of an opaque object on film for study.
  • Immersion Method - The test method in which the test object and the transducer are submerged in a liquid (usually water) that acts as the coupling medium. The transducer is not usually in contact with the test object.
  • Immersion Transducers - A device that focuses sound energy on an object in a water environment. Immersion transducers do not come in direct contact with the object.
  • Immersion Ultrasonic Testing - A NDT that is completed with squirters where the sound travels through a jet of water or by taking the transducer and test object and immersing them in a tank of water.
  • Impedance - The total opposition in an electrical circuit to flow of alternating current.
    - Represents the combination of those electrical properties that affect the flow of current through the circuit.

  • Impedance, Acoustic - See acoustic impedance.
  • Impedance Matching - The process of matching the system impedance to the cable impedance, otherwise error-producing reflections are created.
  • Impedance Method - Eddy current method, which monitors the change in prove impedance; both phase and amplitude.
  • Impedance Plane - The plane formed by the resistance component and the reactance component.
  • Impurities - Elements or compounds whose presence in a material is undesired.
  • Incident Photon - Absorption of x-rays occurs when the x-ray photon is absorbed resulting in the ejection of electrons from the outer shell of the atom. That photon is called the incident photon.
  • Inclusion - Nonmetallic particles, usually compounds in a metal matrix. Usually considered undesirable, though in some cases, such as in free machining metals, inclusions may be deliberately introduced to improve machinability.
  • Incoherent Scattering - The process when the incident x-ray photon ejects a electron from an atom and an x-ray photon of lower energy is scattered from the atom. (Also known as Compton Scattering (C))
  • Incomplete Fusion - Welding fusion which is less than compete. Failure of weld metal to fuse completely with the base metal or preceding bead.
  • Incomplete Joint Penetration (Lack of Fusion) - Welding fusion that fails to penetrate to complete thickness of the materials being joined. Appears as elongated darkened lines of varying length and width which may occur in any part of the welding groove.
  • Incomplete Penetration - Welding root penetration which is less than complete or failure of a root pass and backing pass to fuse with each other.
  • Independent Thinking - The process of being able to think on your own, with out someone else guiding you.
  • Indication - In nondestructive testing, the response from or the evidence of a discontinuity in material condition or structure.
  • Induced Current - Passing an alternating current through a conductor will set up a fluctuating magnetic field. If a second conductor in the form of a closed loop is placed in this field, the action of the fluctuating field moving across the conductor will set up a second alternating current of the same frequency. This is an induced current.
  • Induced Radioactivity - Radioactivity that is created by bombarding a substance with neutrons in a reactor or with charged particles produced by particle accelerators. 
  • Inductance - Ratio of the total magnetic flux-linkage in a coil to the current flowing through the coil.
  • Induction - The process of generating current in a conductor by placing the conductor in a changing magnetic field.
  • Induction Hardening - A method of locally heating the surface of a steel or cast iron part through the use of alternating electric current. It is usually necessary to rapidly cool, or quench, the heated volume to form martensite, the desired hard microstructure.
  • Inductive Reactance - The opposition to a change in alternating current flow.
  • Inductor - A coil.
  • Inertial - The property of matter that causes it to resist any change in its motion.
  • Inherent Defects - Discontinuities which are normal in the material at the time it originally solidifies from the molten state.
  • Initial Pulse - The pulse applied to excite the transducer. It is the first indication on the screen if the sweep is undelayed. Also called the main bang. May refer to an electrical pulse or an acoustic pulse.
  • Insonification - Irradiation with sound.
  • Insulators - Materials that do not have any free electrons. Because of this fact, they do not tend to share their electrons very easily and do not make good conductors of electrical currents.
  • Insulators - Materials that resist the flow of electrons.
  • Intensifying Screen - A layer of material placed in contact with the film to increase the effect of the radiation, thus shortening the exposure.
  • Intensity - The amount of energy a sound has over an area. The same sound is more intense if you hear it in a smaller area. In general, sounds with a higher intensity are louder.
  • Interface - The boundary between two contacting parts or regions or parts.
  • Interface Triggering - Triggering the sweep and auxiliary functions from an interface echo occurring after the initial pulse. Also called IF synchronization.
  • Interference - When two or more sound waves from different sources are present at the same time, they interact with each other to produce a new wave. The new wave is the sum of all the different waves. Wave interaction is called interference.
  • Intergranular Corrosion - Corrosion occurring preferentially at grain boundaries.
  • Intergranular Fracture - Brittle fracture of a metal in which the fracture is between the grains, or crystals, that form the metal. Contrasted to transgranular fracture.
  • Interlock - A device for precluding access to an area of radiation hazard either by preventing entry or by automatically removing the hazard.
  • Internal Probe (coil) - A probe for testing tube (or holes) from the inside. The coil(s) is circumferentially wound on a bobbin.
  • Interpretation - The determination of the source and relevancy of an ultrasonic indication.
  • Inverse Square Law - The equation stating some A = 1 / B2.
  • Ion - A charged atom or molecularly bound group of atoms; sometimes also a free electron or other charged subatomic particle.
  • Ion Pairs - A positive ion and a negative ion or electron having charges of the same magnitude, and formed from a neutral atom or molecule by the action of radiation or by any other agency that supplies energy.
  • Ionization - This process of radiation absorption.
  • Ionization Chamber - An instrument that detects and measures ionizing radiation by observing the electrical current created when radiation ionizes gas in the chamber, making it a conductor of electricity.
  • Ionizing Radiation - Radiation of sufficiently high energy to knock electrons out of the orbits of atoms and molecules, often creating more ionizing radiation and adversely affecting living tissues. Biologically significant radiation is an ionizing dose of radiation above 155 ev which may have carcinogenic, mutagenic, or other health effects in humans.
  • Iridium 192 - A radioactive isotope of the element Iridium which has a half-life of 75 days. It is used extensively as a source of gamma radiation.
  • Irradiation - Exposure to radiation, as in a nuclear reactor.
  • Isomer - One or two or more nuclides having measurable time intervals in different radioactive properties.
  • Isotope - One of two or more atoms of the same element that have the same number of protons in their nucleus but different numbers of neutrons. Most elements have more than one naturally occurring isotope. 
  • Isotropy - A condition in which significant medium properties (velocity, for example) are the same in all directions.