T.O. 33B-1-1Glossary 20CYCLOTRON: A particle accelerator in which the atomic particles are whirled around in a spiral between the ends ofa huge magnet gaining speed with each rotation. The cyclotron is normally used for nuclear research but the particlescan be made to collide with a target to produce X-rays.DD: Symbol for diameter.d: Symbol for distance.d/t RATIO: The working distance for the X-ray tube in relation to the film distance. The working distance, d, and thespecimen thickness, t, are both measured with reference to the source side of the specimen.DAC: Abbreviation for distance amplitude correction; also used to denote electronic distance amplitude correction onsome instruments.DAMPING: Hindering or decreasing the time of vibrations or oscillations in the motion of a body or in an electricalsystem subjected to influences which are capable of causing vibration or oscillation. Compare with attenuation.DAMPING (UT): Limiting the duration of and/or decreasing the amplitude of vibrations, as in damping of a transducerelement; also designates a bond inspection method in which good bonds are verified by damping ultrasonic energytransmitted to the back surface.DAMPING CAPACITY: The ability of a metal to absorb vibration (cyclical stresses) by internal friction converting themechanical energy into heat.DAMPING MATERIAL (UT): Material contained within a search unit in back of the transducer element and used fordamping.DARK ADAPTION: The ability of the eye to adjust so that objects, lights, or colors can be seen in darkened areas.This is important when performing a fluorescent penetrant, fluorescent magnetic particle inspections or wheninterpreting radiographic film.dB: Abbreviation for decibel.DC (DIRECT CURRENT): An electrical current that flows continually in one direction through a conductor.DEAD ZONE: Zone in the test part directly underneath the sound entry surface where discontinuities cannot bedetected; caused by the finite length of the initial pulse, ringing time of the transducer element, and/or electroniccharacteristics of the instrument.DECALESCENCE: A phenomenon, associated with the transformation of alpha iron to gamma iron on the heating(superheating) of iron or steel, revealed by the darkening of the metal surface owing to the sudden decrease intemperature caused by the fast absorption of the latent heat or transformation.DECARBURIZATION: The loss of carbon from the surface of a ferrous alloy as a result of heating in a medium thatreacts with the carbon at the surface.DECAY (MT): The falling off to zero of the current in an electrical circuit. Magnetic fields can also decay in a similarmanner. This is important in demagnetization.
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