R

• Rad - radiation absorbed dose. The basic unit of absorbed dose of ionizing radiation. One rad is equal to the absorption of 100 ergs of radiation energy per gram of matter.
• Radial - In the direction of a radius between the center and the surface of a circle, cylinder, or sphere.
• Radian - A unit in circular measure, an angle subtended at the center of a circle by an arc of equal length to the radius. One radian is equal to 57.296.
• Radiation - Energy traveling in the form of electromagnetic waves, photons, alpha particles (helium nuclei), or beta particles (electrons)
• Radiation Absorbed Dose (RAD) - the quantity that expresses the amount of energy which ionizing radiation imparts to a given mass of matter.
• 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 5 millirems, or in any 5 consecutive days, a dose in excess of 100 millirems.
• Radiation Damage - A general term for the alteration of properties of a material arising from radiation exposure to x-rays, gamma rays, neutrons, heavy-particle radiation or fission fragments in nuclear fuel material.
• Radiation Pressure - The pressure exerted on a surface by electromagnetic radiation.
• Radiation Protection Guide - The total amounts of ionizing radiation dose over certain periods of time which may safely be permitted to exposed industrial groups. These standards, established by the Federal Radiation Council, are equivalent to what was formerly called the "maximum permissible exposure."
• Radiation Sources - An object that emitted radiation.
• Radioactive - Atoms which are energetically unstable and decay to a stable condition by emitting radiation are said to be radioactive.
• Radioactive Activity - The amount of radiation an object is emitting.
• Radioactive Contamination - Deposition of any radioactive material in any place where it is not desired, particularly where it may be harmful.
• Radioactive Decay - The process by which the nucleus of a radioactive isotope decomposes and releases radioactivity.
• Radioactive Elements - Elements that naturally emit radiation when the nucleus of the atoms disintegrate or decay.
• Half-Life - the time required for one half the atoms in a radioactive substance to decay. For example, the radioactive half-life of cesium is 30.174 years. Radionuclides with short half-lives decay quickly and radionuclides with longer half-lives emit energy over longer periods of time.
• Radioactive Material - A material that spontaneously decays (fissions), producing radiation.
• Radioactive Source - A radioactive material being used to generate radiation.
• Radioactive Waste - Equipment and materials (from nuclear operations) which are radioactive and for which there is no further use.
• Radioactivity - spontaneous decay of the nucleus of an atom by the emission of particles, usually accompanied by electromagnetic radiation. It is also defined as the mean number of nuclear transformations occurring in a given quantity of radioactive material per unit time, expressed in either becquerels (Bq) or curies (Ci). Most radionuclides have multiple forms of radioactive emissions, and are classified according to their principal decay modes. The most common types of radiation are Alpha, Beta and Gamma radiation.
• Radioactivity Concentration Guide - The concentration of radioactivity in an environment which results in doses equal to those in the radiation protection guide. This Federal Radiation Council term replaces the former "maximum permissible concentration."
• Radiograph - a photographic recording produced by the passage of radiation through a subject onto a film.
• Radiographer - Any individual who performs or who, in attendance at the site where the sealed source or sources are being used, personally supervises radiographic operations and who is responsible to the licensee for assuring compliance with the requirements of these regulations and the conditions of the licenses.
• Radiographic Code - A code for specifying minimum standards related to radiographic practices.
• Radiographic Exposure Device - Any instrument containing therein, in which the sealed source or shielding thereof may be moved, or otherwise change, from a shielded to unshielded position for purposes of making a radiographic exposure.
• Radiographic Film - A type of film that is sensitive to a certain type of radiation allow an image to form when exposed.
• Radiographic Interpretation - The determination of the cause and significance of subsurface discontinuities indicated on the radiograph. The evaluation as to the acceptability or rejectibility of the materials is based upon the judicious application of the radiographic specifications and standards governing the material.
• Radiographic Qualification Test - A procedure for determining the optimum value of the d/t ratio, or the proper working distance of an x-ray tube or a radioactive source.
• Radiographic Screens - Metallic or fluorescent sheets used to intensify the radiation effect on films.
• Radiography - The process of making a radiograph
• Radio frequency Display - The presentation of unrectified signals on a cathode ray tube. See also video presentation.
• Radioisotopes - elements that are atomically unstable and radioactive.
• Radiology - That branch of medicine which uses ionizing radiation for diagnosis and therapy.
• Radionuclides - A nuclide that is radioactive.
• Radium - A radioactive element with the atomic number 88 and an atomic weight of 226. In nature, radium is found associated with uranium, which decays to radium by a series of alpha and beta emissions. Radium is used as a radiation source.
• Rads - An absorbed does of 0.01 joules of energy per kilogram of tissue.
• Range (Ultrasonic Testing) - The maximum ultrasonic path length that is displayed. See also sweep length.
• Range Control - A means of expanding the pattern obtained on the cathode ray tube so that any portion of the total distance being tested can be presented.
• Rarefaction - The thinning or separation of particles in a propagating medium due to the relaxation phase of an ultrasonic cycle. Opposite of compression. A compressional wave is composed of alternating compressions and rarefactions.
• Ratchet Marks - Ridges on a fatigue fracture that indicate where two adjacent fatigue areas have grown together. Ratchet marks usually originate perpendicular to a surface and may be straight or curved, depending on the combination of stresses that is present.
• Ray - A beam of energy of small cross section.
• Rayleigh Waves - An ultrasonic wave that propagates along the surface of a test object. The particle motion is elliptical in a plane perpendicular to the surface, decreasing rapidly with depth below the surface. The effective depth of penetration is considered to be about one wavelength.
• RBE Dose - Relative biological effectiveness. An RBE dose is the dose measured in rems.
• Real-Time Radiography - A radiograph is produced electronically rather than on film so there is very little lag time.
• Receiver - The section of the ultrasonic instrument that amplifies echoes returning from the test object. Also, the transducer that picks up the echoes.
• Recrystallization - (1) The change from one crystal structure to another, such as occurs on heating or cooling through a critical temperature. (2)The formation of a new, strain-free grain structure from that existing in cold-worked metal, usually accomplished by heating.
• Rectified Alternating Current - By means of device called a rectifier, which permits current to flow in one direction only, alternating current can be converted to direct or unidirectional current. This differs from direct current in that the current value varies from a steady level. This variation may be extreme, as inn the case of half-wave rectified single-phase AC or slight, as in the case of three-phase rectified AC.
• Rectifier - A tube or circuit capable of converting the high voltage alternating wave from into a usable unidirectional voltage wave form.
• Reduction Factor - Dose rate without a shield divided by the dose rate with a shield interposed between a source and a point at which radiation is measured.
• Reference Blocks - A block or series of blocks of material containing artificial or natural discontinuities or one or more reflecting areas at one or more distances from the test surface, which are used for reference in defining the size and distance of defective areas in materials.
• Reference Coil - Coil which enables bridge balancing in absolute probes. Its impedance is close to test coil impedance but does not couple to test material.
• Reference Standard - A reference object containing known reflectors representing accept or reject criteria. - A sample test object.
• Reference Radiographs - A group of radiographs containing images of discontinuities. These can be used as comparison "standards" for acceptability of materials.
• Reflectogram - A picture of recording of the indications presented on the cathode ray tube of the ultrasonic instrument.
• Relectograph - A recording or chart made of either the signals transmitted through a part or reflected back from defects within a part, or both
• Refracted Beam - A beam that occurs in the second medium when an ultrasonic beam is incident at an acute angel on the interface between two media having different sound velocities.
• Refraction - The change in direction of an acoustic wave as the ultrasonic beam passes from one medium into another having a different sound velocity. A change in both direction and mode occurs at acute angles of incidence. At small angles of incidence, the original mode and a converted mode may exist in the second medium.
• Refractive Index -The ratio of the velocity of the incident wave to that of a refracted wave. It is known as the refractive index of the second medium with respect to the first.
• Reinforcement of Weld - (1) In a butt joint, weld metal on the face of the weld that extends out beyond a surface plane common to the members being welded; (2) in a fillet weld, weld metal that contributes to convexity; (3) in a flash , upset or gas pressure weld, the original diameter or thickness.
• Reject - An instrument function or control used for minimizing or eliminating low amplitude signals (electrical or material noise) so that other signals may be further amplified. Use of this control can reduce vertical linearity. Also called suppression.
• Rejection Level - The level above or below which a signal is an indication of a rejectable discontinuity.
• Relative Biological Effectiveness (RBE) - The relative effectiveness of a given kind of ionizing radiation in producing a biological response as compared with 250,000 electron volt gamma rays.
• Relaxation - Relief of stress by creep. Some types of tests are designed to provide diminution of stress by relaxation at constant strain, as frequently occurs in service.
• Relevant Indication - In nondestructive testing, an indication from a discontinuity requiring evaluation.
• Reluctance - the degree of difficulty or resistance of a material to magnetize.
• Remnant Magnetism - The term applied to the magnetism remaining in a magnetic circuit after the magnetizing force is removed.
• REM - See Roentgen Equivalent Man.
• REP - Roentgen equivalent physical. An obsolete unit of radiation dosage, now superseded by the rad.
• Repeatability - Ability to repeatedly produce a measurement or detectable indication with separate measurements or inspections.
• Repetition Rate - The number of pulses generated or transmitted per unit of time (usually seconds).
• Residual Elements - Elements present in an alloy in small quantities, but not added intentionally.
• Residual Field - The field left in a piece of ferromagnetic material when the magnetizing force is reduced to zero.
• Residual Method (Magnetic Particle Testing) - Bath is applied after current has been shut off; that is, the indicating particles are on the part when residual (remaining) magnetic field is present.
• Residual Stress – Internal stress; stress present in a body that is free from external forces or thermal gradients.
• Resistance (R) - The opposition to the flow of electrical current. Measured in ohms
• Resistivity - Reciprocal of conductivity.
• Resistors - Components that are used to control that amount of current flowing in a circuit by adding a specific amount of resistance.
• Resolution - The ability to clearly distinguish signals obtained from two reflective surfaces with a minimum difference in depth. Near surface resolution is the ability to clearly distinguish a signal from a reflector at a minimum distance under the near surface without interference from the initial pulse signal. Far surface resolution is the ability to clearly distinguish signals from the back surface when the sound beam is normal to that back surface.
• Resolving power - A measure of the ability of an ultrasonic system to separate two signals close together in time or distance.
• Resonance - A circuit having an inductor and capacitor connected in series or parallel. When inductive reactance equals capacitive reactance the circuit is tuned or in resonance.
• Resonance Method - A method using the resonance principle for determining velocity, thickness or presence or laminar discontinuities.
• Resonant Circuits - A circuit containing capacitance and inductance.
• Resonant Frequency - The frequency at which a body vibrates freely after being set in motion by some outside force.
• Resultant (Magnetism) - When two or more magnetizing forces operating in different directions are simultaneously applied to a ferromagnetic material, a resultant field is produced, having a direction of the applied magnetizing forces. Such a field is also referred to as a vector field. If either or both of the applied magnetizing forces are themselves varying in direction or amount, the resultant field is moving or swinging in direction and strength. Such a moving resultant field is sometimes referred to as a "swinging field."
• Retentivity - The property of a given material of retaining, to a greater or lesser degree, some amount of residual magnetism.
• RF Display - See radio frequency display.
• Ringing Method - A test method for bonded structures in which disbonds are indicated by increased amplitude of ringing signals.
• Ringing Signals - Closely spaced multiple signals caused by multiple reflections in a thin material. - Signals caused by continued vibration of a transducer.
• Ringing Time - The time that the mechanical vibrations of a transducer continue after the electrical pulse has stopped.
• Rinse - The process of removing liquid penetrant inspection material from the surface of an item by means of washing or flooding with another liquid, usually water. Also termed "Wash."
• R-Meter - An ionization-type instrument designed to measure radiation dose.
• Roentgen - A unit of exposure dose of ionizing radiation. It is that amount of gamma or x-rays required to produce ions carrying 1 electrostatic unit of electrical charge in 1 cubic centimeter of dry air under standard conditions.
• Roentgen Equivalent Man (REM) - The biologically effective does in rems is the radiation does in rads multiplied by a "quality factor" which is an assessment of the effectiveness of that particular type and energy of radiation.
• Roentgens - A measure of radiation intensity of X-rays or gamma rays.
• Root (of a Notch) - The innermost part of a stress concentration, such as the bottom of a thread or groove.
• Root Angle - In a dual element delay line transducer, the angle by which the transducer elements of the delay line are tilted to direct the beams of the two elements to intersect at a specified zone in the medium.
• Root Crack - A crack in either the weld or heat-affected zone at the root of a weld.
• Root Penetration - The depth to which weld metal extends into the root of a joint.