H

• Half-life - The amount of time it takes for half of the atoms in a given mass to decay.
  
• Half Value Layer (HVL) - The depth in given material at which the radiation intensity becomes one half that at the surface of the material.
  
• Half Wave Rectified (ac) - When a single phase alternating current is rectified in the simplest manner, the reverse half of the cycle is blocked out entirely. The result is a pulsating unidirectional current with intervals when no current at all is flowing. This is often referred to as "half-wave" or as pulsating direct current.
  
• Hall Effect - An effect used in the measurement of magnetic fields.
  
• Hardness - Resistance of metal to plastic deformation, usually by indentation. However, the term may also refer to stiffness or temper, or to resistance to scratching, abrasion, or cutting. Indentation hardness may be measured by various hardness tests such as Brinell, Rockwell, Knoop, and Vickers. All indentation hardness tests employ arbitrary loads applied to arbitrary loads applied to arbitrarily shaped indentors, or penetrators.
  
• "Hard" X-rays - A term used to express the quality or penetrating power of x-radiation. Hard x-rays are very penetrating.
  
• Harmonic - A vibration frequency that is an integral multiple of the fundamental frequency.
  
• Hash - See background noise.
  
• Heads - The clamping contacts on a stationary magnetizing unit.
  
• Head Shot - A "shot" of magnetizing current passed through a part or a central conductor while clamped between the head contacts of a stationary magnetizing nit, for the purpose of circular magnetization of the part is called a "head shot." Duration of the passage of the current is usually less than one second.
  
• Health Physics - A term is common use for that branch of radiological science dealing with the protection of personnel from harmful effects of ionizing radiation.
  
• Heat Treatment - Heating and cooling a metal or alloy in such a way as to obtain desired conditions or properties.
  
• Heat Treat Verification - To verify the material has gotten the proper heat treatment a conductivity measurement can be taken.
  
• Heat-Affected Zone - That portion of the base metal which was not melted during brazing, cutting or welding, but whose microstructure and physical properties were altered by the heat.
  
• Henries (H) - A unit of measure for induction.
  
• Hertz - One cycle per second.
  
• High-conductivity copper - Copper which, in the annealed condition, has a minimum electrical conductivity of 100% IACS as determined in accordance with ASTM methods of test.
  
• High-Cycle Fatigue - Fatigue that occurs at relatively large numbers of cycles, or stress applications. The numbers of cycles may be in the hundreds of thousands, millions, or even billions. There is no exact dividing line between low-and high-cycle fatigue, but for practical purposes, high-cycle fatigue is not accompanied by plastic, or permanent, deformation.
  
• High Radiation Area - Any area, accessible to personnel, in which there exists radiation originating in whole or in part within licensed material at such levels that a major portion of the body could receive in any one hour a dose in excess of 100 millirems.
  
• Holes - Any void remaining in a specimen as a result of improper manufacturing processing. Often called gas holes, cavities, or air locks.
  
• Homogenizing - Holding at high temperature to eliminate or decrease chemical segregation by diffusion.
  
• Homogenizing Treatment - A heat treatment of an alloy intended to make it uniform in composition by eliminating coring and concentration gradients.
  
• Horizontal Linearity - A measure of the proportionality between the positions of the indications appearing on the horizontal trace and the positions of their sources.
  
• Horseshoe Magnet - A bar magnet, bent into the shape of a horse shoe so that the two poles are adjacent. Usually the term applies to a permanent magnet.
  
• Hot Cell - A heavily shielded enclosure in which radioactive materials can be handled remotely through the use of manipulators and viewed through shielded windows so that there is no danger to personnel.
  
• Hot Cracks - Appear as ragged dark lines of variable width and numerous branches internally or at the surface.
  
• Hot Spot - The point of retarded solidification caused by an increased mass of metal at the juncture of two sections. It frequently results in shrinkage and inferior mechanical properties at this location.
  
• Hot Tear - A fracture formed in a metal during solidification because of hindered contraction.
  
• Hot Working - Deforming metal plastically at such a temperature and rate that strain hardening does no occur. The low limit of temperature.
  
• Hydrophilic Emulsifiers - A process to remove the excess penetrant with mechanical and chemical action but no diffusion takes place. Hydrophilic emulsifiers are basically detergents that contain solvents and surfactants.
• Hydrogen Embrittlement - A condition of low ductility in metals resulting from the absorption of hydrogen.
  
• Hysteresis - Magnetization curve.