RADICAL  A molecular entity possessing an unpaired electron such as •CH3, •SnH3, •Cl (or Cl•). (In these formulae the dot, symbolizing the unpaired electron, should be placed so as to indicate the atom of highest spin density, if this is possible.) Paramagnetic metal ions are not normally regarded as radicals. C.

RADIOACTIVE CONTAMINATION  A radioactive  substance in a material or place where it is undesirable. IUPAC82..

RADIOACTIVE SOURCE  Any quantity of radioactive material which is intended for use as a source of ionizing radiation . IUPAC82..

RADIOACTIVE TRACER TECHNIQUE  In analysis: a technique for investigating recovery, loss, behavior, and speciation of a microcomponent, in which a radioactively-labeled element or compound chemically identical with the microcomponent is added to the sample, and its behavior is followed by radioactivity  measurements.

RADIOACTIVE WASTE  Unwanted radioactive  materials obtained in the processing or handling of radioactive  materials. IUPAC82..

RADIOACTIVITY  The property of certain nuclides  of showing radioactive decay . IUPAC82..

RADIOALLERGO(AD)SORBENT TEST  (RAST) An isotopic technique for the demonstration of reagins (a class of antibody) directed against specific allergens. B

RADIOANALYTICAL CHEMISTRY  That part of analytical chemistry in which the application of radioactivity  is an essential step in the analytical procedures. Synonymous with analytical radiochemistry . See analytical radiochemistry .

RADIOANALYTIC IMAGING  A technique of separation and analysis of reaction products from a radiolabeled  starting material. The products are separated by thin layer chromatography using an autoradiograph  to quantitatively and qualitatively visualize the results. The technique can be used to study photodegradation, for example. { W. Fostiak et al.  Am. Env. Lab. (Feb. 1991) 10} 

RADIOCHEMICAL PURIFICATION  Chemical separation applied to a radioactive  preparation in order to improve the radiochemical purity . IUPAC82..

RADIOCHEMICAL YIELD  1. For the isotopes  of a specified element, the yield of a radiochemical separation , expressed as a fraction of the activity  originally present. IUPAC82.. Also called the recovery . 2.) In radiation chemistry, the number of species transformed by radiation per 100 eV of absorbed energy: represented by the symbol G, the G-value .

RADIOCHEMISTRY  That part of chemistry which deals with radioactive  materials. It includes the production of radionuclides  and their compounds by processing irradiated  or naturally occurring radioactive  materials, the application of chemical techniques to nuclear studies, and the application of radioactivity  to the investigation of chemical, biochemical or biomedical problems. IUPAC94.

RADIOCHEMISTRY, ANALYTICAL  That part of analytical chemistry in which the application of radioactivity  is an essential step in the analytical procedures. Synonymous with radioanalytical chemistry .

RADIOCHROMATOGRAM  A graphical or other representation of a radiation detector response as a function of time produced by chromatographic separation of a mixture of radioactive species.

RADIOCHROMATOGRAPH  A measuring assembly designed to measure the spatial or time distribution of the activity  of a mixture of radioactive  components after separation by a chromatographic method. IUPAC82..

RADIOCOLLOID  A radioactive substance in colloidal form. The radioactivity usually has little effect on the physicochemical properties of the colloid. See also pseudoradiocolloid .

RADIOECOLOGY  The scientific discipline dealing with the migration, transfer, and concentration of radionuclides  in the environment and with the effect of environmental radioactivity on living organisms.

RADIOELEMENT  An element having no stable  isotope. Also used to indicate an element which is naturally radioactive. NM.

RADIOENZYMATIC ASSAY  An assay of the enzymatic activity of a substance based on the use of a radioactive  substance. IUPAC94.

RADIOEXCHANGE  An exchange reaction  in which one of the exchanging species is radioactive .

RADIOGENIC  Resulting from radioactive decay, usually in reference to natural products such as lead.

RADIOGRAPH  A visual representation of an object produced by placing the object between a source of ionizing radiation  and a photographic plate or film. IUPAC94.

RADIOGRAVIMETRIC ANALYSIS  An analytical procedure in which the activity  of a precipitate is used as a measure of its mass. IUPAC94.

RADIOIMMUNOASSAY  An analytical procedure based on the reversible and non-covalent binding of an antigen (hapten) by a specific antibody employing radioactively labeled antigen (hapten) to measure the fraction of the antigen (hapten) bound to a substoichiometric amount of antibody. IUPAC94.

RADIOIMMUNOASSAY, SOLID PHASE ANTIBODY  Method of radioimmunoassay  employing an antibody bound to a solid phase. IUPAC94.

RADIOIMMUNOELECTROPHORESIS  Immunoelectrophoresis in which either the antibodies or antigens are radioactively labeled. B.

RADIOIODINATION  The process of incorporating the radionuclides of iodine (usually 125I, 131I or 123I) in, or of covalently linking a radioiodinated substance to, a substance. IUPAC94.

RADIOISOTOPE DILUTION ANALYSIS  A method of isotope dilution analysis  making use of a radionuclide . IUPAC94.

RADIOISOTOPE GENERATOR  A system in which a long-lived radioisotope is permanently bound and decays to a shorter-lived daughter radioisotope that may be chemically removed or eluted. The latter process is referred to as milking  the generator. The radioisotope generator is colloquially termed a "cow". KE.

RADIOLUMINESCENCE  Light emissions caused by radiations from radioactive materials. NM.

RADIOLYSIS  The chemical decomposition of materials by ionizing radiation . IUPAC82..

RADIOMETRIC ANALYSIS  A method of analysis in which measurement of the activity  is an essential step. IUPAC94.

RADIOMETRIC ASSAY  A non- competitive binding assay  in which the receptor is labeled instead of the ligand. Synonymous with immunoradiometric assay . KE.

RADIOMETRIC TITRATION  A titration in which a radioactive indicator  is used to monitor the end-point of the titration. IUPAC94.

RADIOPHARMACOLOGY  The study of the preparation and properties of radioactive drugs and their therapeutic and diagnostic uses.

RADIOPOLAROGRAPHY  A tool for studying electrochemical phenomena in which labeled ions are reduced polarographically and the resulting drop is counted. The radioactivity of a given number of drops is proportional to the amount of the element deposited and also to the current. It is a low concentration technique. KE.

RADIORELEASE ANALYSIS  An analytical procedure based on the release of radioactivity  from the reagent by reaction with the analyte . IUPAC94.

RADIORECEPTOR ASSAY  Competitive binding assay  employing a receptor protein that is not an antibody .

RADIOTHERMOLUMINESCENCE  The reappearance of luminescence in radioluminescent materials brought about by heating. Quartz and certain types of glass show the effect. NM.

RADIOTOXICITY  The ability of a substance to give rise to adverse biological toxic effects as a result of the ionizing radiation it emits. NM.

RAFFINATE  In solvent extraction between an organic phase and an aqueous phase, the aqueous phase after equilibrium has been established. Ch.

RANGE  The distance from a radiation  source to the point where the flux density  has vanished. A more explicit term is the mean linear range .

RANGE, MEAN LINEAR  In a given material, for specified charged particles  of a specified energy, the average displacement of the particles  before they stop. IUPAC82..

RANGE, MEAN MASS  The mean linear range  multiplied by the mass density of the material. IUPAC82..

RANGE, RESIDUAL  The penetration depth of a charged particle yet remaining to be traveled before the particle is stopped in the material.

RANGE-ENERGY RELATION  The dependence of the mean linear range  of a charged particle in a particular substance on the particle's initial energy.

RANGE STRAGGLING  The stochastic dispersion of displacement (range) of charged particles about their mean linear range .

RATEMETER  An electronic sub-assembly which gives a continuous indication proportional to the average counting rate  over a predetermined time interval (time constant). IUPAC82..

REACTION, NUCLEAR  A transmutation or nuclear excitation induced by radiation from an external source.

REACTION CHAIN ACTIVATION  See secondary particle activation analysis .

REACTOR, NUCLEAR  A device in which a self-sustaining nuclear fission  chain reaction can be maintained and controlled. The term is sometimes applied to a device in which a nuclear fusion reaction  can be produced and controlled. IUPAC82..

RECEPTOR  A chemical compound on a cell membrane or in a cell that binds other chemicals. NM.

RECOIL  The motion acquired by a particle  through a collision with or the emission of another particle  or electromagnetic radiation . IUPAC82..

RECOIL ATOM  The atom struck by a particle with which it is has undergone either elastic or inelastic scattering or reaction, or an atom or ion remaining after a radiation  has been emitted.

RECOVERY  In trace analysis: the yield of a preconcentration  step expressed as quantities of the concentrated component. C. See also yield, radioactive .

REFERENCE MATERIAL  A homogeneous material, available in sufficient amounts, which can be used for comparing analysis results obtained at different laboratories and/or with different techniques. IUPAC82..

RELATIVE BIOLOGICAL EFFECTIVENESS  The ratio of the appropriate value of the biological effectiveness of the radiation in question to that of x-radiation  with an average specific ionization  of 100 ion pairs per micron of water, for the particular biological effect under consideration and for the condition under which the radiation is received. IUPAC82..

RELATIVE COUNTING  A measurement in which the activity  of a sample is derived from the ratio between the count rates  observed for the sample and for a source of known activity . IUPAC82..

RESOLUTION  The use of the word resolution should be restricted to peak resolution . The concept should be distinguished clearly from that of resolving power , which should be restricted to instruments. The resolving power of an instrument used in an analytical procedure may well have its impact on the selectivity  of the overall procedure. C.

RESOLUTION ENHANCER  1.) Detector designs that reduce degradation of resolution  by compensating for ballistic effects) or charge trapping , for example. 2.) Mathematical procedures, usually called "filters", for improving the ability to accurately resolve close peaks.

RESOLVING POWER  The central position of the response curve of a spectrometer of monoenergetic radiation  divided by the width at one half of its height. Sometimes the width at the 1/eth of its height, sometimes the inverse of the above definition is used. IUPAC82..

RESOLVING TIME  The smallest time interval which must elapse between the occurrence of two consecutive ionizing events or signal pulses, in order that the measuring device be capable of detecting each of them separately.

RESOLVING TIME CORRECTION  Correction to be applied to the observed number of pulses in order to take into account the number of pulses lost during the resolving time . IUPAC82..

RESONANCE  The enhancement of the response of a system to a periodic driving force when the driving frequency is equal to a natural frequency of the system. For nuclear systems, this manifests itself as a particular reaction having a cross section maximum.

RESONANCE ENERGY  The energy of a particle  entering a nuclear reaction, this energy being just sufficiently high to lead to the formation of reaction products in one of their excited states . IUPAC82..

RESONANCE INTEGRAL  The integral, over all or some specified portion of the resonance energy  range, of the cross section divided by the energy of a radiation. IUPAC94.

REST MASS  The mass of a particle in its ground state  and at rest. It represents the Newtonian mass and does not include the additional mass acquired by a particle in motion due to the relativistic effect.

RETENTION  Of atoms undergoing a nuclear transformation , that fraction which remains in or reverts to its initial chemical form. IUPAC82..

REVERSED PHASE CHROMATOGRAPHY  A term of historical interest in liquid-liquid chromatography referring to an elution  procedure in which the stationary phase is non-polar, e.g. paper treated with hydrocarbons or silicones. C.

RNAA  Radiochemical neutron activation analysis. See activation analysis, radiochemical .

ROENTGEN  A unit of exposure. 1 roentgen = 1 R = 2.58 X 10-4 C/kg. (Not a SI unit. 

ROENTGEN EQUIVALENT MAN  (rem) A unit of dose equivalent  which depends on linear energy transfer  and a quality factor . (Not a SI unit.) 1 rem = .01 J/kg = 1 rad  X quality factor . 1 rem = 0.01 sievert (Sv).

RUTHERFORD  An obsolete unit of activity  equal to 106 disintegrations per second. NM.

RUTHERFORD SCATTERING OR RUTHERFORD BACKSCATTERING SPECTROSCOPY  Any technique using high-energy particles directed toward a sample, in which the bombarding particles, after scattering, are detected and recorded as a function of energy and/or angle. The technique is mostly used for determining the depth distributions of elements based on the energy of the backscattered particle. C.