P

Pair Production - An absorption process for X and gamma radiation in which the incident photon is annihilated in the vicinity of the nucleus of the absorbing atom, with subsequent production of an electron and positron pair.
Parabola - An open curve which all points are equidistant from a fixed point and a straight line.
Parallel Circuit - A circuit in which the current has two or more paths to follow.
Paramagnetic (and diamagnetic) - All materials are affected by magnetic fields. Those which are attracted are called paramagnetic. The reaction to a magnetic field of these two classes of substances is very slight indeed. The few materials that are strongly attracted by magnetic fields are called ferromagnetic.
Parasitic Echo - See spurious echo.
Particles - Fundamental units of matter and energy.
Particle Motion - Movement of particles of material during wave propagation.
Particulate Radiation - A stream of atomic or subatomic particles.
Penetrability - The property of a penetrant that causes it to find its way into very fine openings, such as cracks.
Penetrometer - A device for measuring the penetrating power of radiation.
Penetrant - A fluid (usually a liquid but can be a gas) which possesses unique properties that render it highly capable of entering small openings, a characteristic which makes this fluid especially suitable for use in the detection of surface discontinuities which may be present.
Penetrant Testing (PT) - Method that is used to reveal surface breaking flaws by bleedout of a colored or fluorescent dye from the flaw.
Penetration (Ultrasound) - Propagation of ultrasonic energy into a material. See also effective penetration.
Penumbra - The shadow cast when the incident radiation is partly, but not wholly cut off by an intervening body; the space of partial illumination between the umbra, or perfect shadow or all side and the full light. A marginal region on borderland or partial obscurity.
Penumbra Shadow - The shadow of an object with an appreciable size has two distinct regions; one of full-shadow, called the umbra, the other of half-shadow, called the penumbra shadow.
Periodic Table - A chart that lists all of the known elements.
Permanent Magnets - An object that once magnetized will maintain the properties of magnetism indefinitely.
Permeability - The ease with which a magnetic flux can be established. Ratio between flux density, B, and magnetizing force, H. Permeability describes the intrinsic willingness of a material to conduct magnetic flux lines.
Personnel monitoring equipment - Devices designed to be worn or carried by an individual for the purpose of measuring the dose received (e.g. film badges, pocket chambers, pocket dosimeters, film rings, etc.).
Perturbation - Any effect that causes a small change in a physical system and/or changes the value of some given function.
Phantom - A reference standard used to verify the performance of medical diagnostic ultrasound systems.
Phase Angle - The difference in phase between two sinusoidal varying quantities.
Phase Array - A mosaic of transducer elements in which the timing of the elements’ excitation can be individually controlled to produce certain desired effects, such as steering the beam axis or focusing the beam.
Phase Lag - A lag in phase (or time) between the sinusoidal currents flowing at the surface and those below the surface.
Phase Velocity - The velocity of a single frequency continuous wave.
Phasor - A vector describing sinusoidal signals; It has both amplitude and phase.
Photodisintegration (PD) - the process by which an x-ray photon is captured by the nucleus of the atom with the ejection of a particle from the nucleus when all the energy of the x-ray is given to the nucleus.

Photoelectric (PE) - A substance is photoelectric if it ejects electrons when light strikes it.

Photoelectric absorption - A process by which electromagnetic radiation imparts energy to matter.

Photoelectric Effect - When charged particles are released from a material when it absorbs radiant energy.

Photoinductive Imaging (PI) - A powerful, high-resolution scanning and imaging tool

Photon - The elementary particle of electromagnetic energy; light.

Physical properties - The properties of a material that are relatively insensitive to structure and can be measured without the application of force. Examples are density, melting temperature, damping capacity, thermal conductivity, thermal expansion, magnetic properties, and electrical properties.

Pierre and Marie Curie - Two scientists that discovered polonium and radium

Piezoelectric Effect - The ability of certain materials to convert electrical energy into mechanical energy and vice versa.

Piezoelectric Element - A material that vibrates when an electric current passes through it.

Piezoelectric Transducers - A tool that takes an electrical signal and turns it into mechanical vibrations, or takes vibrations and turns it into an electrical signal.

Pig (Radiography) - A container usually made of lead or U 238 used to shield radioactive sources when not in use.

Pin - expansion test - A test for determining the ability of tubes to be expanded or for revealing the presence of cracks or other longitudinal weaknesses, made by forcing a tapered pin into the open end of a tube.

Pipe (Materials) - (1) then central cavity formed by contraction in metal, especially ingots, during solidification; (2) the defect in wrought or cast products resulting from such a cavity; (3) an extrusion defect due to the oxidized surface of the billet flowing toward the center of the rod at the back end; (4) a tubular metal product, cast or wrought.

Pitch - The property of sound that varies with frequency (high and low sounds are at different pitches).

Pitch-Catch -A term describing a test method in which the ultrasonic energy is emitted by one transducer and received by another on the same or opposite surface.

Pitch Line - The location on a gear tooth, approximately midway up the tooth, that crosses the pitch circle, or the equivalent-size disk that could geometrically replace the gear.

Pitchblende - An ore which contains uranium.

Pitting - Small cavities in a metal surface by nonuniform electrodeposition or by corrosion.

Planck Constant - The fundamental constant equal to the ratio of the energy of a quantum of energy to its frequency.

Plane Wave - wave in which points of same phase lie on parallel plane surfaces.

Plastic Deformation - Deformation that remains after removal of the load or force that caused the deformation, or change of shape. Same as permanent deformation.

Plate Wave - See lamb wave.

Plated Crystal - Crystal on which metallic surfaces are deposited for protection and/or to produce surfaces on which the electrical potential can be impressed.

Point of Incidence - Denotes the point at which the center of the sound beam leaves the plastic wedge of an angle beam transducer and enters the test object. See probe index.

Polarization - The process of confining the vibrations of the vector constituting a transverse wave to one direction.

Poling - The process of reorienting crystal domains in certain materials by applying a strong electric field at elevated temperatures. Materials (usually ceramics) so treated exhibit piezoelectric behavior.

Polycrystalline - Pertaining to a solid metal composed of many crystals, such as an ordinary commercial metal.

Pores - (1) Small voids in the body of a metal; (2) In powder metallurgy - minute cavities in a compact, sometimes intentional; (3) minute perforations in an electroplated coating.

Porosity - The property of being porous.

Positron - A Nuclear particle with the mass of an electron but opposite charge (an anti-electron).

Post-Emulsification Penetrant - A type of penetrant containing no emulsifier, but which is cleaned from a surface with water after applying an emulsifier as a separate step. The term is often abbreviated as "P.E." penetrant, or "P.E."method.

Potential Energy - Potential energy is stored energy, energy that can be released or harnessed to do work.

Precleaning (Penetrant ) - The cleaning of parts before testing so that they are free from all foreign material (paint, grease, oil, rust, scale, layout dye, was crayon markings, etc.) which could cover a surface discontinuity and thereby inhibit the entrance of the penetrant liquid.

Presentation (Ultrasound) - The method used to show ultrasonic information. This may include A-scans, B-scans or C-scans, displayed on various types of recorders or cathode ray tube instruments.

Primary Radiation - Radiation arising directly from the target of an x-ray tube or from a radioactive source.

Primary Reference Response Level - The ultrasonic response from the basic calibration reflector at the specified sound path distance, electronically adjusted to a specified percentage of full screen height.

Primary Field - The magnetic field surrounding the coil due to the current flowing through it.

Principal Stresses - The normal stresses on three mutually perpendicular planes on which there are no shear stresses.

Probe (Eddy Current Testing) - Eddy current transducer.

Probe Index (Ultrasound) - The point on a shear wave or surface wave transducer through which the emergent beam axis passes.

Prods (Magnetic Particle Testing) - Two handheld electrodes which are pressed against the surface of a part to make contact for passing magnetizing current through the metal. The current passing between the two contacts creates a field suitable for finding defects with magnetic particles.

Propagation - Advancement of a wave through a medium.

Proportional Limit - The maximum stress at which strain remains directly proportional to stress; the upper end of the straight-line portion of the stress-strain or load-elongation curve.

Proton - A fundamental particle usually found in the nucleus of an atom with a positive charge.

PSI - Acronym for pounds per square inch, a unit of measurement for stress, strength, and modulus of elasticity.

Pulse - A transient electrical or ultrasonic signal.

Pulse Echo Method - An ultrasonic test method in which discontinuities are detected by return echoes from the transmitted pulses.

Pulse-Echo Test - A test that can determine the location of a discontinuity by measuring the time required for a short ultrasonic pulse to travel through the material.

Pulsed Eddy Current - An electromagnetic test technique that drives eddy currents using a pulse of electrical current. The technique is particularly useful in driving eddy currents deeper into materials than is usually achievable with conventional eddy current techniques. The signal is often displayed in the time domain which allows for depth gating and other useful signal processing techniques.

Pulse Length - A measure of pulse duration expressed in time or number of cycles.

Pulse Method - Use of ultrasonic equipment that generated a series of pulses which are separated from each other be a constant period of time, i. e., energy is not sent our continuously.

Pulse Rate - Number of pulses that are transmitted in a unit time (also called pulse repetition rate).

Pulser-Receiver - Used with a transducer and oscilloscope for flaw detection and thickness gauging.

Pulse Repetition Frequency - See repetition rate.

Pulse Tuning - Control of pulse frequency to optimize system response.