E

effective degrees of freedom (ν_eff)

measure of the relative precision of an estimator for an uncertainty or variance, analogous to the degrees of freedom for a Type A evaluation of uncertainty (see Welch-Satterthwaite Formula)

The number of effective degrees of freedom for the uncertainty evaluation can be used to choose a coverage factor that gives a desired approximate coverage probability.

efficiency

See detection efficiency

electrodeposition

deposition of a substance from solution on an electrode by an application of electrical current

electronegativity

measure of the attraction an atom has for electrons in a covalent bond [wikipedia.org]

electron capture (EC)

mode of nuclear decay in which an atomic nucleus is transformed by absorbing an orbital electron, thereby decreasing the atomic number by 1 and leaving the mass number unchanged

Note 1: After electron capture, the orbital electrons rearrange themselves to fill the vacancy left by the captured electron and release energy by either X-ray emission or the Auger effect.
Note 2: Electron capture is considered to be a type of beta decay, although no beta-particle is emitted.

electronic data deliverable (EDD)

report of analytical data delivered to a laboratory’s client in electronic form

electronvolt (eV)

non-SI unit of energy defined as the kinetic energy acquired by an electron passing through a potential difference of 1 V in vacuum, measured to be 1.602 177 33(49) × 10⁻¹⁹ J

Note: Although the electron volt is not an SI unit, it is accepted for use with the SI.

element

type of matter composed of atoms with the same atomic number

Note: An element is a pure substance that cannot be decomposed by chemical means (cf. compound).

eluant; eluent

(in chromatography) the fluid that enters a chromatographic bed during elution

eluate

(in chromatography) the effluent that emerges from a chromatographic bed during elution

elute

(in chromatography) to extract (a substance) from a chromatographic bed by passing a fluid over it

elution

(in chromatography) act or process of eluting a substance from a chromatographic bed — sometimes colloquially called “washing”

emulsion

colloidal suspension in which both phases are liquids; a suspension of tiny droplets of one liquid in another, in which it is insoluble

enriched uranium (EU)

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

enrichment

See isotopic enrichment

equilibrium

state of a system in which positive and negative rates of change are balanced so that the net rate of change is approximately zero (see also radioactive equilibrium)

Er

atomic symbol for erbium

error (of an estimator)

in statistics, the difference between an estimator and the value of the parameter being estimated

error (of measurement)

“result of a measurement minus a true value of the measurand” [VIM]

Note: Metrologists distinguish between the concepts of error of measurement and uncertainty of measurement.

Es

atomic symbol for einsteinium

escape peak

in a gamma-ray spectrum, a peak produced when interactions of incident gamma-rays with the detector produce secondary photons of discrete energies, one or more of which escape from the detector without depositing their energy (see also single escape peak and double escape peak)

estimated covariance

estimated value of the covariance of two random variables, or of two input estimates

The estimated covariance of input estimates x_i and x_j is denoted by u(x_i, x_j).

estimator

statistic whose value is used to estimate the value of a parameter

Eu

atomic symbol for europium

exception

in data verification, an instance of nonconformance to specified requirements

expanded uncertainty

product, U, of the combined standard uncertainty, u_c(y), and a coverage factor, k, which is chosen so that the interval from y − U to y + U has a high probability of containing the value of the measurand

expectation

for a random variable, X, a measure of central tendency of X, denoted by E(X) or μ_X, which may be thought of as a weighted average of all the possible values of X, where each value’s weight is proportional to its probability of occurrence

If X is a discrete random variable, this intuitive definition is adequate. In general, if X is an arbitrary random variable defined on a probability space (Ω,ℱ,P), where Ω denotes the set of all elementary outcomes of an experiment, ℱ denotes a σ-field of events, and P denotes a probability measure on ℱ, then the expectation of X is defined as

E(X) = ∫_Ω X dP

The expectation of X may also be called the expected value or the mean of X.

Note: The terms elementary outcome, probability space, σ-field, event, measure, and probability measure, as well as the concept of integration with respect to a measure, are defined in references on advanced probability theory or measure theory.

expected value

expectation

experimental standard deviation

The experimental standard deviation of a series of observations x₁, x₂, …, x_n, denoted by s(x_k), equals

s(xk) =

√

1 n − 1

n ∑ k = 1

(xk − x)2

where x denotes the arithmetic mean of x₁, x₂, …, x_n. The experimental standard deviation of the mean, denoted by s(x), equals s(x_k) / n^1/2.

exponential distribution

type of probability distribution, characterized by one parameter, usually denoted by λ, and having the probability density function

f(x) =	{	λe−λx,	if x ≥ 0
		0,	if x < 0

An exponential distribution describes the lifetime of an atom of a radionuclide, in which case the parameter λ equals the decay constant of the radio­nuclide. An expo­nential dis­tribu­tion also describes wait­ing times between events in a Poisson process. For example, if the instru­ment background for a radiation counter follows the Poisson model and the mean count rate is r, then the wait­ing times between counts are expo­nen­tially dis­trib­uted with param­eter r.

exposure

ratio of the ionization charge produced by X-rays or gamma-rays in air to the asso­ciated mass of air

The SI derived unit of ex­po­sure is the cou­lomb per kilo­gram (C/kg). The tradi­tional non-SI unit of ex­po­sure is the roentgen (R).