D

dalton (Da)

unified atomic mass unit

Note: The name “dalton” and the symbol “Da” are not accepted for use with the SI.

data package

report of analytical data from a laboratory, often including supporting documentation, such as instrument printouts, photocopies of logbook pages, etc.

data quality assessment (DQA)

“a statistical and scientific evaluation of the data set to determine the validity and performance of the data collection design and statistical test, and to determine the adequacy of the data set for its intended use.” [EPA 2000]

data quality objectives (DQOs)

“qualitative and quantitative statements derived from the DQO Process that clarify study objectives, define the appropriate type of data, and specify tolerable levels of potential decision errors that will be used as the basis for establishing the quality and quantity of data needed to support decisions.” [EPA 2000]

data quality objectives process (DQO Process)

“a systematic planning tool to facilitate the planning of environmental data collection activities. Data quality objectives are the qualitative and quantitative outputs of the DQO Process.” [EPA 2000]

data reduction

calculation of final results of measurements from the raw data

data V & V

data verification and data validation

data validation

“an analyte- and sample-specific process that extends the evaluation of data beyond method, procedural, or contractual compliance (i.e., data verification) to determine the analytical quality of a specific data set.” [EPA QA/G-8]

(data validation) qualifier

“code applied to the data by a data validator to indicate a verifiable or potential data deficiency or bias.” [EPA QA/G-8]

data validator

“an individual (typically an independent third part) responsible for conducting data validation activities.” [EPA QA/G-8]

data verification

“the process of evaluating the completeness, correctness, and conformance/compliance of a specific data set against the method, procedural, or contractual requirements.” [EPA QA/G-8]

data verifier

“an individual (typically en employee of the field or laboratory organization whose operations are being verified) responsible for conducting data verification activities.” [EPA QA/G-8]

daughter nuclide; daughter product

decay product

Db

atomic symbol for dubnium

dead layer

layer of inactive material on the surface of a semi­conductor detector, normally part of the electrical contact, which does not respond to incident radiation in the same manner as the semi­conductor material and which acts as an absorber

dead time

1. time required for a radiation counter to process an event, during which it is unable to process other events (cf. resolving time)
2. total amount of time in a radiation counting measurement during which the radiation counter is processing events and therefore is unable to process new events
3. ratio of total dead time (definition 2) to real time, usually expressed as a percentage

dead water

water devoid of tritium (e.g., fossil water)

decay

See nuclear decay and radioactive decay

decay chain

sequence of nuclides ordered so that each member of the sequence after the first is an immediate decay product of its predecessor in the sequence

decay constant (λ)

physical constant associated with a radionuclide, equal to the radionuclide’s mean instantaneous fractional decay rate, or for a single atom the probability of decay in a short time interval, divided by the length of the interval

Note 1: The decay constant λ also equals ln(2) / T_1/2, where T_1/2 denotes the half-life of the radionuclide.
Note 2: The activity of a collection of N atoms of the radionuclide equals λN.

decay product

nuclide produced from a given radionuclide in a series of one or more nuclear decays — also called daughter or descendant (nuclide)

decision level

See critical value

deconvolution

In the radiochemistry laboratory, the term deconvolution usually refers to the mathematical operation of resolving a multiplet to identify and quantify the individual peaks that contribute to it.

Note: Convolution has a rigorous mathematical definition, but in the radiochemistry laboratory it generally means the blurring of a radiation spectrum that occurs because of imperfect energy resolution. Given a mathematical function that describes the detector’s response to incident radiation at each energy, one can largely reverse the effects of the convolution in an operation called deconvolution, which transforms the blurred spectrum to a clearer one.

degrees of freedom

in a statistical estimation, the number of observations minus the number of parameters estimated

density

1. The noun density, when it follows the name of a measurable quantity, indicates the quotient of that quantity and its associated volume.
2. mass density

depleted uranium (DU)

uranium in which the isotopic abundance of ²³⁵U is lower than its natural abundance (cf. enriched uranium)

depletion layer

active region of material in a semi­conductor detector that is depleted of charge carriers by the application of a voltage and which can produce electrical pulses in response to ionizing radiation

derived quantity

“quantity defined, in a system of quantities, as a function of base quantities of that system” [VIM]

derived unit

unit of measurement for a derived quantity (cf. base unit)

desiccant

hygroscopic substance used to remove moisture from the air

desiccator

container used to dry material or keep it dry, usually by enclosing it in a small space with a desiccant

detect

1. <radiation> to produce an indication when a radiation is emitted
2. <analyte> to decide on the basis of a measurement that an analyte is present (e.g., in a test sample)

detection capability

ability of a measurement process to detect the analyte, or to discriminate between small positive values of the measurand and zero. The detection capability may be expressed in terms of the minimum detectable value.

detection decision

the decision about whether an analyte is present (in a test sample), or whether the value of the measurand is positive

detection efficiency

probability that a photon or particle of a specified type emitted from a radioactive source will be detected by the radiation detector

detection limit

1. minimum detectable value
2. any of several other terms defined as "detection limits" by various authorities

detector

“device or substance that indicates the presence of a phenomenon without necessarily providing a value of an associated quantity” [VIM]

Note: In a radiochemistry laboratory, this term usually refers to a radiation detector.

dewar (or Dewar)

double-walled container with an evacuated space between the walls, often silvered on the innermost surface to prevent heat transfer, used for storing liquefied gases

Note: A common use for a dewar in the radiochemistry laboratory is to hold the liquid nitrogen in which the cold finger of a high-purity germanium detector is immersed.

digestion

dissolution of solid material, typically involving strong acid, heat, and possibly fusion, usually done to convert a test portion to an aqueous solution before chemical separations

dimension (of a quantity)

See the referenced document VIM

disintegration

nuclear disintegration

disintegrations per minute (dpm)

non-SI unit for activity, equal to 1 min⁻¹

disintegrations per second (dps)

becquerel (Bq)

Note: The SI name for this unit is "becquerel" and the SI symbol is "Bq". The SI name and symbol are always preferred over the non-SI "disintegrations per second" and "dps".

distribution

See probability distribution

distribution function

cumulative distribution function

dose

See absorbed dose and dose equivalent

dose equivalent

product of the absorbed dose in living tissue and the quality factor that expresses the biological effectiveness of the particular type of ionizing radiation in the organs receiving the dose.

The SI unit of dose equivalent is the sievert (Sv). The traditional non-SI unit of dose equivalent is the rem, which equals 0.01 Sv.

dosimeter

device for measuring exposure to ionizing radiation or absorbed dose

dosimetry

measurement of exposure to ionizing radiation or absorbed dose

double escape peak

in a gamma-ray spectrum, a peak produced when incident gamma-rays of a certain energy interact with the detector by pair production and deposit all of their energy in the detector except 1022 keV, the difference in energy being the result of the escape of both of the 511 keV photons that are produced when the positron from the electron-positron pair is annihilated. (see also single escape peak)

Note: The double escape peak occurs at energy E_γ − 2m_ec², where E_γ is the energy of the incident gamma-ray.

dpm

disintegrations per minute

drift

“slow change of a metrological characteristic of a measuring instrument” [VIM]

dry

to remove water from a sample, especially by heating at a moderately elevated temperature, without otherwise altering the sample’s composition (cf. ash)

Drying is often one of the first steps performed on a sample of solid material during its preparation for radiochemical analysis.

dry weight; dry mass

mass of material after drying but before ashing if applicable (cf. ash weight and wet weight)

Ds

atomic symbol for darmstadtium

duplicate

second measurement of the same measurand made for the purpose of checking the precision of the measurement process (see also laboratory duplicate)

Dy

atomic symbol for dysprosium

dynode

any of the series of electrodes between the photocathode and the anode in a photomultiplier tube, which have increasingly positive biases and whose purpose is to produce secondary emission of electrons