SAFEGUARDS  Measures employed to prevent or detect the diversion of nuclear material and to protect against sabotage. GNST.

SALTING OUT  Improving the extraction of a substance by the addition of an electrolyte to the aqueous phase. C.

SARGENT CURVES OR SARGENT DIAGRAM  Graphs of logarithms of radioactive disintegration constants of beta-emitting radioisotopes against corresponding logarithms of their maximum beta-particle energies. D.

SATURATION  Of an irradiated element for a specified isotope , the steady state reached when the disintegration rate  of the nuclide  formed is equal to its production rate. IUPAC82..

SATURATION ACTIVITY  For a specified isotope , the value of the activity  of an irradiated element, when a state of saturation  is reached. IUPAC82..

SATURATION ANALYSIS  A type of competitive binding assay  where the specific reactor substance binding sites are all occupied (saturated) with ligand.

SATURATION CORRECTION  Also known as saturation factor, the factor applied to an induced activity that transforms the activity into a hypothetical activity in an irradiation of infinite duration, that is, into a saturation activity .

SCALER  A sub-assembly for counting electrical pulses and containing one or more scaling circuits . IUPAC82..

SCALING CIRCUIT  An electronic circuit which produces an output pulse after a specified number of pulses has been received at its input.

SCATTERING  A process in which a change in direction or energy  of an incident radiation  is caused by interaction with a particle , a system of particles , or a photon . IUPAC82..

SCATTERING, ELASTIC  Scattering  in which the total kinetic energy is unchanged. IUPAC82..

SCATTERING, INELASTIC  Scattering  in which the total kinetic energy changes. IUPAC82..

SCATTERING RECOIL COINCIDENCE SPECTROMETRY  In depth profiling, a technique combining Rutherford backscattering spectroscopy  and elastic recoil detection analysis . The recoil is detected in coincidence with the scattered beam particle.

SCAVENGING  In radiation chemistry : binding radicals or free electrons  with a scavenger . In radiochemistry : the use of a precipitate to remove from solution by adsorption  or coprecipitation, a large fraction of one or more radionuclides .

SCINTIGRAM  An image of the distribution of activity obtained with a scintillation camera following the internal administration of a radionuclide. NM.

SCINTILLATING MATERIAL  Any substance constituting an appropriate medium for the detection of radiation  by means of the scintillation  phenomenon. IUPAC82..

SCINTILLATION  Burst of luminescence  of short duration caused by an individual high-energy particle . IUPAC82..

SCINTILLATION COUNTER  Radiation counter  incorporating a scintillation detector . IUPAC82..

SCINTILLATION CRYSTAL  A scintillation material  that is crystalline in nature (as opposed to polymeric, for example).

SCINTILLATION DETECTOR  A radiation detector  using a medium in which a burst of luminescence radiation  is produced along the path of an ionizing particle . IUPAC82..

SCINTILLATION SPECTROMETER  A measuring assembly incorporating a scintillation detector  and a pulse amplitude analyzer , used for determining the energy spectrum  of certain types of radiation . IUPAC82..

SCINTILLATOR  A finite quantity of scintillating material  intended to be the element sensitive to radiation  in a scintillation detector . IUPAC82..

SCISSION  The stage in the fission  mechanism when the highly deformed nucleus divides into at least two fragments.

SCRUBBING  In liquid-liquid distribution, the process of removing impurities from the separated phase containing the main substance. C.

SEALED SOURCE  A radioactive source sealed in a container or having a bonded cover, where the container or cover has sufficient mechanical strength to prevent contact with and dispersion of the radioactive material under the conditions of use and wear for which it was designed. NM.

SECONDARY PARTICLE ACTIVATION ANALYSIS  An activation  method in which energetic particles from a primary reaction on a nuclide of interest subsequently undergo a secondary activation reaction on another nuclide producing a more easily detected radioactivity. FR.

SECONDARY RADIATION  Radiation  emitted by any matter irradiated with electromagnetic or ionizing radiation . IUPAC82..

SELF-ABSORPTION FACTOR  Of a radiation  source, the ratio between the amount of radiation  emitted by the source and the amount of radiation  produced by the radioactive nuclei  present in the source. Synonymous with source efficiency .

SELF-RADIOLYSIS  The radiolysis  of a substance or mixture brought about by one of the substance's or mixture's own radioactive  components.

SELF-SHIELDING  The lowering of the flux density  in the inner part of a sample due to absorption  in the outer layers of the sample. IUPAC82..

SEMICONDUCTOR  Material whose conductivity, due to charges of both signs, is normally in the range between that of metals and insulators and in which the electric charge carrier density can be changed by external means. IUPAC82..

SEMICONDUCTOR DETECTOR  Radiation detector  using a semiconductor  in which free electric charges are produced along the path of an ionizing particle . IUPAC82..

SEMICONDUCTOR DETECTOR, DIFFUSED JUNCTION  A semiconductor detector  in which the P-N or N-P junction is produced by diffusion of donor  or acceptor  impurities. IUPAC82..

SEMICONDUCTOR DETECTOR, P.I.N.  A semiconductor detector  consisting of a compensated region between a P and an N region. The compensated region is often referred to as "intrinsic". IUPAC82..

SEMICONDUCTOR DETECTOR, SURFACE BARRIER  A semiconductor detector  utilizing a junction due to a surface inversion layer. IUPAC82..

SENSITIVITY  In diagnostic tests, the number of test results registered as true positives in relation to the actual number of positives in the group tested. The minimum signal that can be detected satisfactorily. The lowest concentration of test substance measurable in an assay, or the minimal difference in test substance concentrations distinguishable by a given assay, usually a function of the steepness of the assay curve. NM.

SEPARATION ENERGY  Of a particle, the energy required to remove that particle (e. g. , neutron, proton, alpha) from the nucleus.

SEQUESTERING AGENT  Or sequestrants, are compounds capable of binding metal ions so that they no longer exhibit their normal reactions in the presence of precipitating agents. Most sequestrants owe their action to the formation, with the metal ion, of stable coordination compounds of chelates. NM.

SERIAL DILUTION  The progressive dilution, by the same factor, of standard or sample in a row of tubes so that the first tube contains the highest concentration of test substance.

SHADOWING  The local reduction of the particle flux density  due to the presence of a nearby absorber. GNST.

SHIELDING  Protecting against penetrating radiation by using an absorbing layer of matter. Also, such matter itself.

SIEVERT  Unit of dose equivalent . (Not capitalized. Symbol = Sv.) 1 sievert = 1 gray  X quality factor .

SIGMOID CURVE  S-shaped curve, approaching linearity in the middle and curved at either end. NM.

Si(Li) DETECTOR  A lithium-drifted silicon detector. A diffused junction semiconductor detector  in which silicon is the base solid state material.

SINGLE CHANNEL PULSE HEIGHT ANALYZER  See pulse amplitude selector .

SINGLE COMPARATOR METHOD  In quantitative activation analysis , a method in which a known amount of activatable isotope is irradiated simultaneously and under identical conditions with an unknown amount of the isotope. NAC.

SNAP  Space Nuclear Auxiliary Power; a radioactive source for power generation in satellites and space craft.

SOFT RADIATION  Radiation whose particles or photons have a low energy and consequently do not penetrate materials easily. M.

SOLID STATE TRACK DETECTOR  An insulating solid in which the paths of nuclear particles suffer radiation damage of sufficient permanancy that they may be rendered visible through chemical etching processes. NAC.

SOLUTE  The minor component of a solution which is regarded as having been dissolved by the solvent . C.

SOLVENT  A liquid (usually the major component of a solution) which is used to dissolve a solute  or solutes. C.

SOLVENT EXTRACTION  Process of removing one or more constituents of a mixture from immiscible solvents by preferential solubility in a specific solvent. D.

SORBENT  Material which has a large capacity for absorbing moisture or other gas or fluid. D.

SORPTION  It is sometimes difficult or impossible to discriminate experimentally between adsorption  and absorption : in such cases it is convenient to use the non-committal term sorption. In ion exchange, sorption is the uptake of electrolytes or non-electrolytes by ion exchangers  through mechanisms other than pure ion exchange . C.

SOURCE, EXTENDED  In contrast to a point source , below, a source of radiation whose size is not constrained to approximate a point.

SOURCE, POINT  A source of radiation which is confined to a small point or spot.

SOURCE, RADIOACTIVE  Any quantity of radioactive  material which is intended for use as a source of ionizing radiation . IUPAC94.

SOURCE STRENGTH  The strength of a radioactive source, meaning the amount of radioactive material contained in it, usually expressed in curies or becquerels. NM.

SPALLATION REACTION  A nuclear reaction in which the projectile induces the ejection of neutrons, protons  and/or light heavy ions from the struck target nucleus.

SPECIAL NUCLEAR MATERIAL  Fissionable and other material related to military use.

SPECIATION  A term that refers to the physicochemical forms of a radionuclide  under a particular set of ambient conditions (pH, Eh, ligands present, etc.).

SPECIFIC ENERGY  The energy imparted by ionizing radiation  to matter. NM.

SPECIFIC IONIZATION  The number of ion pairs formed per unit distance along the track of an ionizing particle  passing through matter. IUPAC82..

SPECIFICITY  In radioimmunoassays , a measure of the discrimination between antigens by the antigen-antibody site of the antibody . KE.

SPECTROMETER, ALPHA (, BETA, GAMMA-RAY, X-RAY)  A measuring assembly incorporating a radiation detector  and a pulse amplitude analyzer , used for determining the energy spectrum  of alpha (beta, gamma, x) radiation. IUPAC82..

SPECTROMETER, ANTI-COMPTON GAMMA-RAY  See gamma-ray spectrometer, anti-Compton .

SPECTROMETER, CRYSTAL DIFFRACTION  A spectrometer , in which diffraction by a crystal is used to obtain the energy spectra of electromagnetic radiation  as well as of slow neutrons . IUPAC82..

SPECTROMETER, X-RAY  See spectrometer, alpha (, beta, gamma-ray, x-ray ).

SPECTRUM (,RADIATION)  The components of radiation arranged in order of their wavelengths, frequencies or quantum energies. IUPAC94.

SPIKE  The isotopically distinct label (radioactive or stable) added to a sample undergoing analysis by any of several isotopic methods.

SPIKING  The process of adding a spike  to a sample undergoing analysis.

SPILL  A contamination  as a result of an accident during some process or procedure involving radioactivity.

SPIN, NUCLEAR  The intrinsic angular momentum of an elementary particle or system of particles such as a nucleus. NM.

SPINTHARISCOPE  An instrument for viewing scintillations of charged particles on a luminescent screen, usually with the aid of a microscope. M.

SSE-IDA  See sub- and superequivalence isotope dilution analysis .

STANDARD MATERIAL  A reference material  for which, for specified element concentrations, values are recommended by some official body. These values should be based on the consistent results obtained by using independent analytical techniques. IUPAC82..

STANDARD REFERENCE MATERIAL  Term exclusively used for a standard material  issued by the National Bureau of Standards, USA. IUPAC82..

STAR  A nuclear event, recorded in photographic emulsion , in which the tracks of three or more charged particles radiate from a single point. NM.

STOPPING POWER  Of a substance, for charged particles  of specified energy, the average energy loss in passing through a thin layer of that substance, divided by the thickness of that layer. IUPAC82..

STRAGGLING  A term used to express the fact that the ranges  of charged particles of a given energy in matter are not constant but show a small spread about the mean range. This uncertainty in the range occurs because the loss of energy by charged particles is not a continuous process, but one in which energy is transferred in discrete amounts to the electrons in the matter through which the particle is passing. NM.

STRIPPING  The process of back-extraction of a substance from an extract, usually into an aqueous phase. C.

STRONTIUM UNIT  A measure of the concentration of 90Sr in food and in the body measured relative to calcium. One strontium unit is 1 millibecquerel 90Sr per gram calcium. NM.

SUB- and SUPEREQUIVALENCE ISOTOPE DILUTION  A technique of substoichiometric radiochemical analysis  in which two series of solutions containing sample and spike  are compared; one is isotopically diluted with increasing amounts of carrier  and the other has multiples of sample and spike but no carrier. The amount of unknown element in the sample is obtained by graphic analysis following activity ratio determinations. FR.

SUBSTOICHIOMETRIC RADIOCHEMICAL ANALYSIS  An isotope dilution  technique combining a radioactive tracer and a reagent which is intentionally applied in amounts that are insufficient to react completely with the analyte .

SUB-TRACE ANALYSIS  Trace analysis with sample size 10-3- 10-4 g and constituent content £ 100 ppm (0.01%). C.

SUM PEAK  In a spectrum of radiation , the part of the response corresponding to the total absorption in a detecting material of the combined energies of two coincident radiations .

SUM PEAK METHOD  A method of analysis in which the sum peak  of two gamma rays is counted and in which the intensity ratios of the sum peak to the single peak can be used and changes in the ratios due to the chemical environments of the emitting nuclide can be observed. P.

SUPEREQUIVALENCE ISOTOPE DILUTION  See sub- and superequivalence isotope dilution .

SUPERHEAVY ELEMENT  A term often used with reference to elements of atomic number  well beyond 110.

SUPERNATANT  The clear solution associated with a settled, centrifuged, or filtered precipitate.

SURFACE BARRIER SEMICONDUCTOR DETECTOR  See semiconductor detector, surface barrier .

SURVEY METER  A battery-powered portable device containing a gas ionization chamber or other detection device for monitoring radiation levels. NM.

SYNCHROCYCLOTRON  An ion accelerator, the chief components and configurations of which are similar to those of a cyclotron and in which the phase of the accelerating potential is synchronized with the frequency of the accelerated particles by frequency modulation to compensate for relativistic increases in mass at high speeds.

SYNCHROTRON  An accelerator in which ions are accelerated around a fixed circular path by a radiofrequency potential and maintained in the path by a magnetic field that varies with time.

SYNCHROTRON RADIATION  Electromagnetic radiation produced by any charged particle forced to travel in a nonlinear orbit such as a proton in a storage ring. NAC.

SYNERGISM  A characteristic exhibited when two separate agents in combination produce an effect greater than the sum of that produced by each agent separately.

SZILARD-CHALMERS EFFECT  The rupture of the chemical bond between an atom  and a molecule of which the atom  is a part, as a result of a nuclear reaction  of that atom . IUPAC82..