 [D]- 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.
- DAUGHTER (PRODUCT) Any nuclide which follows a specified radionuclide in a decay chain.
- 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.
- 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.
- 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.
- DECAY CURVE A graph showing the relative amount of radioactive substance remaining after any time interval.
- 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.
- 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.
- DETECTOR, 1/n A neutron detector for which the cross section of the detection reaction varies inversely with neutron speed.
- 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.
- 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.
- 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 xrays 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.
- DISINTEGRATION CONSTANT See decay constant.
- DISINTEGRATION, NUCLEAR Nuclear decay involving a splitting into more nuclei or the emission of particles.
- 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.
- 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. 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.
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