U

• UT - Abbreviation for the ultrasonic method of nondestructive testing.
• Ultrasonic - A term referring to acoustic vibration frequencies greater than about 20,000 hertz.
• Ultrasonic Absorption - The damping of ultrasonic waves as they pass through a medium. See attenuation coefficient.
• Ultrasonic Simulation (UTSIM) - A user interface integrating a CAD model representing a part under inspection and an ultrasound beam model.
• Ultrasonic Spectrum - Usually, the frequency range from 20,000 to 107 hertz. But may extend much higher in special applications.
• Ultrasonic Spectroscopy - Analysis of the frequency content of an acoustic wave. Generally performed mathematically using a fast Fourier transform.
• Ultrasonic Testing - The transmission of high-frequency sound waves into a material to detect imperfections or to locate changes in material properties.
• Ultrasonic Vibrations - Vibrational waves of a frequency above the hearing range of the normal human ear are referred to as ultrasonic, and the term therefore includes all those waves of a frequency of more than approximately 20,000 cycles per second. Also known as ultrasonic waves.
• Ultrasonic Waves - Sound waves too high in frequency for humans to hear.
• Ultrasonically Sound Material - A material having no discontinuities which cause discernible ultrasonic indications at the required test sensitivity level.
• Ultrasound - A test using ultrasonic waves to create an image of the inside of an object.
• Ultraviolet Light - Light lying just beyond the violet end of the visible spectrum and having wavelengths shorter than approximately 4,000 angstroms.
• Underbead Crack - A subsurface crack in the base metal near a weld.
• Undercut - In welding, a groove melted into the base metal adjacent to the toe, or edge, of a weld and left unfilled.
• Unrestricted Area - Any area, entry into which is not controlled.
• Unsharpness, Geometrical - The fuzziness or lack of definition in a radiographic image resulting from the source size, object to film distance and the source to object distance.
• Unstable Atom - The nuclei of some atoms where the binding energy is not strong enough to hold the nucleus together.
• Unstable Nucleus - When an imbalance of protons and neutrons causes the nucleus to change.
• Uranium 238 (Depleted Uranium) - spend uranium, an isotope of uranium used for shielding sources. It is slightly radioactive, but its activity is slightly radioactive, but its activity is insignificant and does not add to any radiation leakage from the shielded source