DAC  Derived air concentration .  

DALTON  A unit of molecular weight  used in some life sciences. Its use is discouraged.

DATING, RADIOACTIVE  The determination of the radioactive age  of an object from its content of radioactive  substances and of their daughter products . IUPAC82.

DAUGHTER (PRODUCT)  Any nuclide  which follows a specified radionuclide  in a decay chain . IUPAC82.

DEAD TIME  Constant and known value imposed on the resolving time  by a paralysis circuit , usually in order to make the correction for resolving time losses  more accurate. IUPAC82..

DEAD 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  or dead time . IUPAC82..

DE BROGLIE WAVELENGTH  In the quantum mechanical description of matter, the wavelength of a particle, from which all behavior is understandable, and whose magnitude relative to the environment determines whether or not classical physics is a justifiable approximation to reality.

DECAY CHAIN  A series of nuclides  in which each member transforms into the next through nuclear decay  until a stable nuclide  has been formed. Synonymous with radioactive chain  and radioactive decay series .

DECAY CONSTANT  For a radionuclide , the probability l for the nuclear decay  of one of its nuclei in unit time, i.e.,  the rate constant for radioactive decay, a first order reaction. It is given by l=(1/Nt)(dNt/dt), in which Nt is the number of nuclei of concern existing at time t. Synonymous with disintegration constant. IUPAC82..

DECAY CURVE  A graph showing the relative amount of radioactive substance remaining after any time interval. IUPAC82..

DECAY CURVE ANALYSIS  A mathematical procedure for deconvoluting a decay curve into the separate contributions from each radioactivity in a complex sample.

DECAY ENERGY  The total energy change when a nuclide  in its ground state  undergoes radioactive decay to a daughter product  in its ground state. It is identical to the Q-value  for the spontaneous reaction.  

DECAY, RADIOACTIVE  Nuclear decay  in which particles  or gamma radiation  are emitted or the nucleus  undergoes spontaneous fission . IUPAC82..

DECAY ( NUCLEAR)  A spontaneous nuclear transformation .

DECAY SCHEME  A graphical representation of the energy levels of the members of a decay chain  showing the path by which nuclear decay occurs.

DECAY SERIES  See decay chain .

DECONTAMINANT  Any chemical reagent(s) used in the act of decontamination .

DECONTAMINATION  The act of removing contamination  from materials, organisms, an environment, etc.

DECONTAMINATION FACTOR  The ratio of activity  after decontamination  to that before decontamination.

DELAYED BETA DECAY  Radioactive decay  to a daughter product  which is unstable towards emission of a beta-particle  which is then emitted in some fraction of decay events.

DELAYED COINCIDENCE  A measurement using a coincidence circuit  in which it is required that in order to be recorded, the occurrence of two events be separated by an electronically imposed time delay.

DELAYED FISSION  Radioactive decay  to a daughter product  which is unstable towards fission  and consequently undergoes fission in a measurable fraction of decay events.

DELAYED NEUTRON ACTIVATION ANALYSIS  A method for measuring heavy elements, particularly uranium, thorium, and plutonium by activation to induce fission leading to delayed-neutron emitting products from which the neutrons are measured.  

DELAYED NEUTRON EMISSION  Radioactive decay  to a daughter product  which is unstable towards emitting a neutron and consequently does so in some fraction of decay events. Half-lives for delayed neutron emission are long compared to neutron emission associated directly with nuclear reactions  or fission .

DELTA RAYS  Secondary electrons, ejected by the primary ionizing interactions of charged particles passing through matter, provided their energy exceeds a few hundred eV.

DENSITOMETRY  Measurement of the response of an emulsion layer as blackening. The negative log of the transmittance of light is proportional to the electron exposure. J.

DEPLETED MATERIAL  Any substance in which the isotopic abundance of a stable isotope has been reduced from its natural value by artificial or natural means.

DERIVATIVE ACTIVATION ANALYSIS  A method of activation analysis  in which the element or chemical entity to be determined is either replaced by, or complexed with, a surrogate substance for which activation analysis has an enhanced sensitivity. FR.

DERIVED AIR CONCENTRATION  A concentration of a given radionuclide in air, obtained by means of a stylized model for the constantly maintained activity concentration of that radionuclide in air, which if breathed by the reference man for a working year of 2000 hours under conditions of light physical activity (breathing rate 1.2 m3/h) would result in an inhalation of one ALI (annual limit of air intake). Also the concentration which for 2000 hours of air immersion would lead to the irradiation of any organ or tissue to the appropriate limit. WASTE.

DESCENDANT  In a radioactive decay chain , any member of that chain except the parent .  

DETECTION EFFICIENCY  The ratio between the number of particles or photons  detected and the number of similar particles or photons emitted by the radiation  source. IUPAC82..

DETECTOR, 1/n  A neutron detector  for which the cross section  of the detection reaction varies inversely with neutron speed. IUPAC82..

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

DETECTOR EFFICIENCY (, INTRINSIC)  The ratio of the number of particles  or  photons  detected to the number of similar particles or photons which have struck face of a radiation detector . When multiplied by the geometry factor , it yields the absolute detector efficiency .

DETECTOR, FOIL  See foil detector  

DETECTOR, LIQUID SCINTILLATOR  A scintillation detector  of which the scintillating medium is a liquid. The sample is often dissolved in the scintillating liquid. IUPAC82..

DETECTOR, RADIATION  An apparatus or substance for the conversion of radiation  energy to a form of energy which is suitable for detection and or measurement.

DETECTOR, SCINTILLATION  See scintillation detector  

DETECTOR, SEMICONDUCTOR  See semiconductor detector  

DETERMINAND  The element or chemical species to be determined. HRC.

DEUTERON  A hydrogen nucleus of mass number  2.

DICHROMATOGRAPHY  A technique based on the differential absorption of two x-rays or gamma-rays, which closely bracket the critical absorption edge  of an element.

DIFFUSED JUNCTION SEMICONDUCTOR DETECTOR  See semiconductor detector, diffused junction  

DIGESTION  A chemical process for softening or solubilizing a material with heat, chemical reagents, and moisture.  

DIS  Deep inelastic scattering.

DISCRIMINATOR  A basic function unit comprising an electronic circuit which gives an output pulse for each input pulse whose amplitude lies above a given threshold value. IUPAC82..

DISINTEGRATION CONSTANT  See decay constant .

DISINTEGRATION, NUCLEAR  Nuclear decay  involving a splitting into more nuclei  or the emission of particles . IUPAC82..

DISINTEGRATION RATE  See activity .

DISTRIBUTION RATIO  The ratio of the total analytical concentration of a substance in the stationary phase to its total analytical concentration in the mobile phase, usually measured at equilibrium.

DISPLACEMENT ANALYSIS  One of several general terms for competitive binding assay , most often used to refer to a variant technique wherein the addition of tracer is delayed to enhance assay sensitivity. NM.

DISPLACEMENT, RADIOACTIVE  Originally established empirically, this connects the type of radioactive decay (a or b) with the displacement, caused by the change in nuclear charge, of the daughter relative to the parent in the periodic table of elements. NM.

DONOR  In a solid state detector, an impurity that is added to a pure semiconductor material to increase the number of free electrons. M.

DOPPLER BROADENING  Frequency spreading that occurs in single-frequency radiation when the radiating atoms do not all have the same velocity and may each give rise to a different Doppler shift . M.

DOPPLER SHIFT  The amount of change in the observed frequency of a wave due to the Doppler effect, that is, relative motion of the source and detector. M.

DOPPLER SHIFT ATTENUATION  The dependence of a gamma-ray line shape on by velocity changes in a decelerating ion. The effect can be used to determine the stopping power  of heavy ions in various materials if an emitter with a known lifetime is used.

DOSE  A general term denoting the quantity of radiation  (energy) absorbed. For special purposes, it must be appropriately qualified, c. q. absorbed, maximum permissible, mean lethal.  

DOSE, ABSORBED  The energy imparted to matter by ionizing radiation  in a suitable small element of volume divided by the mass of that element of volume. IUPAC82..

DOSE EQUIVALENT (, EFFECTIVE)  The absorbed dose  multiplied by the quality factor  and the product of all other modifying factors N, aimed at expressing on a common scale, for different types of radiations and distributions of absorbed dose , the biological effects associated with an exposure . IUPAC82.. Also called just the dose equivalent . NCRP.  

DOSE METERS  or

DOSIMETERS  An instrument that measures the total dose  of nuclear radiation received during a given time period. M.

DOSIMETRY  The technique of measurement of dose .

DOUBLE IRRADIATION TECHNIQUE  In activation analysis , the irradiation of identical samples at positions of very different fast-to-thermal neutron flux. The technique is used to resolve interferences of different analyte elements leading to the same final product. KE.

DOUBLE LABELING  labeling with two isotopes at two different sites on the same molecule.

DOUBLE RADIOIMMUNOASSAY  A radioimmunoassay  in which small amounts of antibody-antigen  complex serve as antigen in a second antibody-antigen reaction that acts to scavenge  the labeled substance.

DOUBLING TIME  The amount of time required before the quantity of a substance doubles when the rate of growth is approximately exponential.

DRIFT (OF A CHARGED PARTICLE)  The movement of current carriers in a semiconductor under the influence of an applied voltage. M.

DSCEMS  Depth selective conversion electron Mssbauer spectroscopy.

DVI  Prefix to an element indicating another element in the same column but two rows lower in the periodic table having the light elements located at the top. Derived from the Sanskrit word for two. See also eka .

DWELL TIME  The time increment during which pulses are stored in a multichannel pulse height analyzer  operating in the multiscaling mode. (See multiscaling.)

DYNODES  An electrode, used in photomultipliers, whose primary function is secondary emission of electrons. M.