 [S]- 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.
- SATURATION ACTIVITY For a specified isotope , the value of the activity of an irradiated element, when a state of saturation is reached.
- 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.
- SCALING CIRCUIT An electronic circuit which produces an output pulse after a specified number of pulses has been received at its input.
- SCATCHARD PLOT In radioimmunoassays , for example, a graph of bound-to-free ratio vs the concentration of bound antigen. KE.
 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. - SCATTERING, COMPTON See Compton effect.
- SCATTERING, ELASTIC Scattering in which the total kinetic energy is unchanged.
- SCATTERING, INELASTIC Scattering in which the total kinetic energy changes.
- 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.
- SCAVENGER A reagent used for scavenging.
- 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.
- SCINTILLANT Scintillating material, fluor.
- SCINTILLATING MATERIAL Any substance constituting an appropriate medium for the detection of radiation by means of the scintillation phenomenon.
- SCINTILLATION Burst of luminescence of short duration caused by an individual highenergy particle.
- SCINTILLATION COCKTAIL The solution of fluors used for liquid scintillation counting. B.
- SCINTILLATION COUNTER Radiation counter incorporating a scintillation detector.
- 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.
- 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.
- SCINTILLATOR A finite quantity of scintillating material intended to be the element sensitive to radiation in a scintillation detector.
- SCINTIPLAST Plastic scintillator. D.
- 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.
- SECULAR EQUILIBRIUM See equilibrium, secular.
- SEGRE CURVE See beta stability line.
- SELF-ABSORPTION The absorption of radiation by the emitter.
- 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.
- 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.
- SEMICONDUCTOR DETECTOR Radiation detector using a semiconductor in which free electric charges are produced along the path of an ionizing particle.
- 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.
- 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".
- SEMICONDUCTOR DETECTOR, SURFACE BARRIER A semiconductor detector utilizing a junction due to a surface inversion layer.
- SENSITIVE VOLUME OF A DETECTOR That part of the volume of a radiation detector in which radiation can be detected.
- 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.
- SEPARATION, RADIOCHEMICAL See radiochemical separation.
- 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.
- SERIES, RADIOACTIVE See decay chain.
- SF Spontaneous fission.
- 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.
- SNR Signal-to-noise ratio.
- 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 noncommittal term sorption. In ion exchange, sorption is the uptake of electrolytes or nonelectrolytes by ion exchangers through mechanisms other than pure ion exchange. C.
- SOURCE EFFICIENCY See self-absorption factor.
- 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.
- SOURCE, SEALED See sealed source.
- SOURCE STRENGTH The strength of a radioactive source, meaning the amount of radioactive material contained in it, usually expressed in curies or becquerels. NM.
- SOURCE, VOLUMINOUS See source, extended.
- SPALLATION PRODUCT A product of a spallation reaction.
- 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 ACTIVITY See activity, specific.
- SPECIFIC BURN-UP See burn-up, specific.
- 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.
- SPECIFICITY In radioimmunoassays , a measure of the discrimination between antigens by the antigen-antibody site of the antibody. KE.
- SPECT Single photon emission computerized tomography. J.
- SPECTRAL HARDENING See hardening.
- SPECTROGRAM A spectrum as recorded by a spectrometer.
- SPECTROGRAPH Graphical representation of a spectrum.
- SPECTROMETER A measuring assembly used for determining the spectrum of a radiation.
- 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.
- 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.
- SPECTROMETER, SCINTILLATION See scintillation spectrometer.
- 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.
- SPECTRUM ANALYSIS The interpretation of the information present in an energy spectrum in terms of radiation energy and intensity.
- SPECTRUM, MEASURED See spectrogram.
- 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.
- SPONTANEOUS FISSION See fission, spontaneous.
- SRA See substoichiometric radiochemical analysis.
- SRCS See scattering recoil coincidence spectrometry.
- SSE-IDA See sub- and superequivalence isotope dilution analysis.
- SSTD Solid state track detector.
- STABLE Not radioactive.
- 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.
- STANDARD REFERENCE MATERIAL Term exclusively used for a standard material issued by the National Bureau of Standards, USA.
- 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.
- 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 £ 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.
- Sv Symbol for the unit, the sievert.
- 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.
- SYNROC The name given to a group of specially formulated zirconium-based ceramics that were originally developed for immobilizing high-level (radioactive) waste.
- 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.
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