A

absolute

The adjective absolute is sometimes used with the name of a physical or mathematical quantity to emphasize that the quantity stands alone, without reference or comparison to, or division by, any other quantity, as in absolute activity, absolute error, and absolute standard uncertainty. When the word absolute is used in this manner, it often can be omitted without changing the meaning of the term. (See also massic, specific, volumic, relative, and absolute value.)

absolute activity

activity (cf. massic activity, specific activity, volumic activity, activity concentration)

absolute error

error of measurement (cf. relative error)

absolute standard uncertainty

standard uncertainty (cf. relative standard uncertainty)

absolute value

The absolute value of a number x equals x if x is nonnegative and equals −x otherwise. Note that the absolute value of a number is always nonnegative. (Compare this usage of absolute with its usage in the terms above.)

absorbed dose

energy imparted to material by ionizing radiation, divided by the associated mass of material

 

The SI derived unit of absorbed dose is the gray (Gy), which equals 1 J/kg. The traditional non-SI unit of absorbed dose is the rad, which equals 0.01 Gy.

absorption (chemical)

intake of particles of one material, especially a fluid, into another material, generally a liquid or solid (cf. adsorption)

absorption (of radiation)

transfer of some or all of the energy of a radiation to matter it traverses [IUPAC, modified]

abundance

1. probability of emission of a given radiation during the decay of an atom of a radionuclide; radiation emission probability — also called intensity
2. isotopic abundance

Ac

atomic symbol for actinium

accreditation

official recognition and documentation of conformance to a standard; in particular, the recognition by an accrediting organization such as a state that a laboratory conforms to specified standards

accuracy of a measurement

“closeness of the agreement between the result of a measurement and a true value of the measurand” [VIM]

Accuracy is a qualitative concept.

Note: Some authors define accuracy differently. Some say that a measurement process is accurate to the degree that it is unbiased, even if it is imprecise. Other authors define accuracy for a measurement process in terms of both precision and (absence of) bias. According to the definition given above, accuracy is a characteristic of a measurement or the result of a measurement, not a measurement process, and although an imprecise or biased measurement process will tend to produce inaccurate results, it may produce accurate results by chance from time to time.

actinide

any element with atomic number between 89 and 103, including actinium, thorium, protactinium, uranium, neptunium, plutonium, americium, and curium

action level

theoretical value of a quantity such as the concentration of a contaminant in a particular medium or a dose limit, at which action is considered necessary to mitigate potentially harmful effects on people or the environment

activation

inducement of radioactivity by irradiation

activation analysis

analysis based on the measurement of characteristic radiations emitted by nuclides formed by activation (see also neutron activation analysis)

activity (for radionuclides)

mean rate of radioactive decay in a quantity of material

The SI derived unit of activity is the becquerel (Bq), which equals 1 s⁻¹. The traditional non-SI unit of activity is the curie (Ci), which equals 3.7 × 10¹⁰ Bq.

Note 1: The term activity alone is synonymous with absolute activity. The term may also be modified by the word massic or specific to denote activity divided by mass, or by the word volumic to denote activity divided by volume. (See also activity concentration.)
Note 2: The term activity may be qualified by specifying one or more radionuclides (e.g., ²³⁸U activity) or the type of decay (e.g., gross alpha activity).
Note 3: Since radio­active decay is an inherently random phenomenon, the concept of activity is defined in terms of the mean rate of decay, not the actual rate observed during any particular time interval. For a collection of N atoms of a particular radionuclide with decay constant λ, the activity of the collection exactly equals λN.

activity concentration

quotient of the activity of a quantity of material and its volume; volumic activity

Note: The term activity concentration is often used by radiochemists more generally to mean the quotient of the activity of a quantity of material and its size, where the size may be the mass, volume, area, etc.

adjustment (of a measuring instrument)

“operation of bringing a measuring instrument into a state of performance suitable for its use” [VIM]

adsorption

adhesion of one substance onto the surface of another [RHH] (cf. absorption)

Ag

atomic symbol for silver

Agreement State

state that has signed an agreement with the Nuclear Regulatory Commission under which the state regulates the use of byproduct, source, and small quantities of special nuclear material in that state — source: http://www.nrc.gov/reading-rm/basic-ref/glossary.html

Al

atomic symbol for aluminum

aliquant

fractional part that does not evenly divide the whole (cf. aliquot)

aliquot

fractional part that evenly divides the whole (cf. aliquant)

Note: The term aliquot in common laboratory usage has come to mean either an aliquot or aliquant of material. In most cases the definition of aliquant better reflects the intended meaning.

alpha decay

radioactive decay of an atomic nucleus accompanied by the emission of an alpha-particle

alpha-emitter

alpha-emitting radionuclide

alpha-emitting

capable of undergoing alpha decay

alpha-particle (α-particle)

particle consisting of two protons and two neutrons (a ⁴He nucleus) emitted from an atomic nucleus during certain types of radioactive decay

alpha-particle spectrometry

technique for measuring the activities of radionuclides by analyzing the spectrum of their emitted alpha-particles (often called alpha spectrometry or colloquially alpha spec)

alpha radiation

radiation consisting of alpha-particles

alpha scintillation cell

sealed container, the walls of which are coated with a scintillator such as zinc sulfide, with a transparent window at one end, which can be filled with a gas such as helium or nitrogen containing some quantity of a gaseous alpha-emitting radionuclide such as ²²²Rn and used in conjunction with a scintillation counter to measure the activity of the radionuclide (see also Lucas cell)

alternative hypothesis (H₁ or H_A)

in a statistical hypothesis test, the hypothesis that is accepted if the data provide sufficient evidence to reject the null hypothesis

Am

atomic symbol for americium

amount of substance

measurable quantity defined as the number of elementary entities in a collection of elementary entities of specified type (such as atoms of a specified element or molecules of a specified compound)

Note: Amount of substance is defined not as a pure number but rather as a number of entities of a certain type. The type of entity must be specified.

amu

abbreviation and obsolete unit symbol for atomic mass unit (see unified atomic mass unit)

analysis

identification or quantification of components of a sample or item (see also chemical analysis, qualitative analysis and quantitative analysis)

Note: Some analytical chemists use the term analysis to mean instrumental analysis.

analyst

person who performs analyses

analyte

in an analysis of a sample or item, the component analyzed for

analyte-free

containing none of the analyte (also called blank)

Note: The term blank has so many slight variations of meaning that analyte-free may be less confusing when the intended meaning is the one stated above. For example, to refer to a normal test sample that happens to be analyte-free as a “blank sample” might cause confusion, since the term blank sample could easily be interpreted as method blank or reagent blank.

analytical chemistry

the theory and practice of chemical analysis

analytical method

See measurement method

analytical procedure

See measurement procedure

analytical process

See measurement process

analyzer

See pulse height analyzer

ancestor (radionuclide)

radionuclide that produces a given nuclide in a series of one or more radio­active decays — also called parent (radionuclide)

anion

negatively charged ion (cf. cation)

annihilation

interaction between a particle and its antiparticle that results in the disappearance of the original particles and the production of new photons or particles

annihilation peak

photopeak at 511 keV in a gamma-ray spectrum, produced by the annihilation of an electron and positron, which results in the production of two photons of approximately 511 keV each (only one of which is usually detected)

anthropogenic radionuclide

radionuclide produced by human activity (politically correct term for man-made)

anticoincidence counting

radiometric counting technique that lowers inter­fer­ence levels by reject­ing any event that is accom­panied by one or more events occur­ring with­in a speci­fied time interval (cf. coincidence counting)

Ar

atomic symbol for argon

areic

The adjective areic, when applied to the name of a measurable quantity, indicates the quotient of that quantity and its associated area.

arithmetic mean

average

As

atomic symbol for arsenic

ash

to heat material to a temperature at which most organic components are gradually oxidized (cf. dry)

ash weight; ash mass

mass of material after ashing (cf. dry weight and wet weight)

assay

testing or analysis of a sample, or an instance of such a test or analysis

At

atomic symbol for astatine

atomic mass

rest mass of an atom in its ground state [IUPAC]

atomic mass constant

one-twelfth of the rest mass of an atom of ¹²C in its ground state, measured to be 1.660 538 782(83) × 10⁻²⁷ kg [CODATA-2006]

atomic mass unit

unified atomic mass unit

atomic number (Z)

number of protons in an atomic nucleus — also called proton number

atomic symbol

symbol consisting of one, two, or three letters, used to denote an atom or element (e.g., “H” for hydrogen)

atomic weight

relative atomic mass

attenuation (of radiation)

decrease in intensity of radiation due to interactions with matter

attenuation coefficient

linear attenuation coefficient

Au

atomic symbol for gold

Auger effect

ejection of an electron, called an Auger electron, from one of an atom’s outer electron shells accompanying the filling of a vacancy in an inner shell

 

The Auger effect and X-ray emission are alternative means of releasing energy when the vacancy is filled.

Auger electron

orbital electron ejected from an atom in the Auger effect

autoradiograph

image produced on a photographic film by radiation from a radioactive source placed near the film

autoradiography

the use of autoradiographs to detect radioactivity (e.g., to locate “hot spots” in a radioactive source)

average

sum of a finite nonempty set of values divided by the number of values — also called arithmetic mean

Avogadro constant; Avogadro’s number (N_A)

number of entities in a mole of substance, defined as the number of atoms in 0.012 kg of ¹²C and measured to be N_A = 6.022 141 79(30) × 10²³ mol⁻¹ [CODATA-2006]