PENETRATION (RT): A qualitative term used to describe the degree to which radiation is capable of penetrating a
given object. Penetration is usually a function of the applied tube voltage in X-rays or equivalent voltage in isotope
PENETRATION TIME (PT): The time allowed for the penetrant to enter into surface discontinuities, i.e., the length of
time elapsing between the application of the penetrant to the part and removal of penetrant.
PENUMBRA (RT): 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, on all sides and the full light. A
marginal region of borderland of partial obscurity.
PERSONNEL MONITORING EQUIPMENT (RT): 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.)
PERIODIC TABLE: A tabular arrangement of elements according to their properties.
PERMEABILITY (MT): The ease with which a material can become magnetized. It is the relationship between field
strength and the magnetizing force.
PERMEABILITY (MT): The ease with which a magnetic field or flux can be set up in a magnetic circuit. It is not a
constant value for a given material, but is a ratio. At any given value of magnetizing force, permeability is B/H the
ratio of flux density, B, to magnetizing force H.
PERMANENT MAGNETS: A body that possesses the ability to retain or hold a large amount of the applied magnet
field after the active power of the field is removed.
PERMANENT MOLD: A metal mold (other than an ingot mold) of two or more parts that is used repeatedly for the
production of many castings of the same form. Liquid metal is poured in by gravity.
PERMANENT SET: Plastic deformation that remains upon releasing the stress that produces the deformation.
PHASE: In periodic changes of any magnitude varying according to a simple harmonic law (as ultrasonic vibrations,
alternating electric currents, etc.), the point or stage in the period to which the variation has advanced, considered in its
relation to a standard position; can be expressed in degrees.
PHASE ANALYSIS: An instrumentation technique which discriminates between variables in the test part by the
different phase angle changes which these conditions produce in the test signal.
PHASE ANGLE: The angular equivalent of the time displacement between corresponding points on two sine waves of
the same frequency.
PHASE SHIFT: A change in the phase relationship between two alternating quantities of the same frequency.
PHI (0): Symbol for the sound beam angle as measured from the normal to a sound entry or sound reflecting surface;
the Greek letter Phi.
PHOTOELECTRIC ABSORPTION (RT): A process by which electromagnetic radiation imparts energy to matter.
PHOTOGRAPHIC EMULSION (RT): See EMULSION.
PHOTOGRAPHIC FOG (RT): Fog caused solely by the properties of an emulsion and the processing conditions, i.e.,
the total effect of inherent fog and chemical fog.