S

S

atomic symbol for sulfur

sample

1. (noun) portion of material taken from a larger quantity of material — also called a physical sample (see also laboratory sample and test sample)
2. (noun) randomly chosen subset of a statistical population, typically selected for the purpose of making inferences about one or more characteristics of the entire population
3. (intransitive verb) to collect a physical sample
4. (transitive verb) to collect a physical sample from

sampling bias

See bias (of sampling)

saturation

in an ionization chamber, the state where the voltage applied to the electrodes is sufficient to reduce recombination to a negligible level and allow essentially all ion pairs produced in the gas to be collected by the electrodes, but where the voltage is not sufficient to cause gas amplification

Sb

atomic symbol for antimony

Sc

atomic symbol for scandium

scaler

electronic device for counting pulses from a radiation detector

scattering

deflection of radiation by an interaction with matter

scavenger

substance that reacts with (or otherwise removes) a trace component (as in the scavenging of trace metal ions) or traps a reactive reaction intermediate [IUPAC]

scintillation

burst of luminescence of short duration caused by an individual energetic particle [IUPAC]

scintillation counter

radiation counter, typically including a photomultiplier tube, that operates by counting the scintillations produced when radiation impinges on a scintillator

scintillation counting

technique for measuring radiation by counting the scintillations produced when radiation impinges on a scintillator

scintillator

material that emits scintillations in response to incident radiation (see also fluor and phosphor)

Se

atomic symbol for selenium

secular equilibrium

radioactive equilibrium in a decay chain where the the half-life of the ancestor radionuclide is much longer than those of the descendants, and where the parent-daughter ratios approach limiting values within a period of time much less than the half-life of the ancestor (cf. transient equilibrium).

self absorption

absorption of radiation within the material that contains the radiation-emitting atom

sensitivity

ratio of the change in an output to a change in an input (e.g., ratio of the change in the response of a measuring instrument to a change in the stimulus).

Note: The term sensitivity is also commonly used as a synonym for detection capability, although some (including Keith) consider this usage to be incorrect.

sensitivity coefficient

If Y = f(X₁,X₂,…,X_N) is a measurement function, and x₁,x₂,…,x_N are input estimates for a particular measurement, then the sensitivity coefficients for the measurement are the partial derivatives, ∂f / ∂x_i, evaluated at (x₁,x₂,…,x_N).

separation

See chemical separation

separation factor

in ion-exchange chromatography, the ratio of the distribution coefficients for two ions, determined under identical experimental conditions

The degree to which the separation factor differs from 1 determines the separability of the two ions.

Sg

atomic symbol for seaborgium

SI

International System of Units

Si

atomic symbol for silicon

sievert (Sv)

special name for the SI derived unit of dose equivalent, equal to 1 J/kg

sigma (σ)

In statistics the Greek letter sigma (σ) is commonly used to denote the standard deviation of a random variable or of a population. In statistical quality control, the term “sigma” and the symbol σ are also frequently used for an estimated standard deviation used to construct a control chart. In metrology the term “sigma” is sometimes used colloquially for a standard uncertainty, and “k-sigma” is sometimes used colloquially for an expanded uncertainty with a coverage factor of k.

significance level (α)

upper bound for the probability of a type I error in a statistical hypothesis test

Si(Li) detector

radiation detector that detects radiation absorbed in a wafer of lithium-drifted silicon

Si(Li) detectors may be used for example to detect X-rays or charged particles, such as alpha-particles.

single 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 511 keV, the dif­fer­ence in energy being the result of the escape of one of the two 511 keV photons that are pro­duced when the posi­tron from the electron-positron pair is annihilated (see also double escape peak)

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

Sm

atomic symbol for samarium

smear

swipe

Sn

atomic symbol for tin

solubility

measure of the ability of one substance (the solute) to dissolve in another (the solvent) at a given temperature, expressed as the maximum ratio of mass of solute to volume of solvent

solvent extraction

chemical separation technique based on selective removal of components of a mixture into a solvent in which the components are more soluble

sorption

either absorption or adsorption

source

See radioactive source

specific

massic

specific activity

massic activity

specificity (of an analytical method)

ability to provide a measured value for the analyte that is inde­pendent of other com­ponents of the sample

spectra

Latin plural form of spectrum

Note: Many non-Latin speakers tend to use the word spectra incorrectly as a singular noun.

spectrometer

radiation detector and associated electronics for measuring radiation spectra

spectrometry

measurement of the radiation spectra that physical systems produce or with which they interact as a means of obtaining information about the systems and their components (cf. spectroscopy) [IUPAC, modified]

spectroscopy

study of physical systems by the radiation spectra that they produce or with which they interact (cf. spectrometry) [IUPAC, modified]

spectrum (or radiation spectrum)

(pl. spectra or spectrums) “The components of radiation arranged in order of their wavelengths, frequencies or quantum energies. For particle radiation they are arranged in order of their kinetic energies.” [IUPAC]

spike

1. (transitive verb) to add an analyte to (a sample), typically in the form of a measured amount of a standard solution
2. (noun) normal or artificial sample that has been spiked (e.g., a matrix spike or laboratory control sample)

spillover

recording of radiations of a particular type or energy in channels of the multi-channel analyzer beyond their designated region of interest

spontaneous fission (SF)

mode of nuclear decay in which an atomic nucleus splits into two or more nuclei (spontaneous nuclear fission)

spurious error

error of measurement produced by an abnormal or unexpected cause, such as a human blunder or instrument malfunction

Sr

atomic symbol for strontium

stable nuclide

nuclide that is not not capable of undergoing nuclear decay

stability

“ability of a measuring instrument to maintain its metrological characteristics with time” [VIM]

standard

See (measurement) standard

standard deviation

measure of dispersion for a random variable, equal to the positive square root of the variance

standard error

In statistics the term standard error denotes the standard deviation of an estimator. However, metrologists seldom use this term because they consider it to be a misnomer. The statistician’s concept of a standard error is somewhat similar to a metrologist’s concept of a standard uncertainty.

Note: Metrologists sometimes claim that the term “standard error” is incorrect. In fact the term is completely correct for statisticians but should be avoided by metrologists.

standard normal distribution

the normal distribution with mean zero and variance one

standard reference material (SRM)

certified reference material produced by the National Institute of Standards and Technology (NIST)

standard operating procedure (SOP)

document that describes in detail the steps for performing a routine task

standard uncertainty

uncertainty of a measured result expressed as an estimated standard deviation (see also combined standard uncertainty)

The standard uncertainty of a result, x, may be denoted by u(x).

Stapleton’s Rule

criterion for deciding whether activity is present in a Poisson count­ing measure­ment, based on the fact that the statistic

Z = 2 ×

√ NS + d  tS   −   √ NB + d  tB √ 1 tS   +   1 tB

where N_S denotes the sample count, N_B denotes the blank count, t_S denotes the sample count time, t_B denotes the blank count time, and d is a suitably small constant, has approximately the standard normal distribution [due to Dr. James H. Stapleton, Department of Statistics, Michigan State University]

Note: Stapleton’s Rule may be implemented by using an appropriate expression for the critical value of the net count or net count rate.

stationary phase

phase in a chromatographic system that remains stationary (cf. mobile phase)

statistic

mathematical function of the data in a statistical experiment

Note: A statistic is a random variable.

statistical control

state of a process, such as a measurement process, in which essentially all of the observed variations are due to the statistical variability inherent in the process and not to abnormal, potentially correctable conditions (assignable causes)

statistical quality control (SQC)

quality control using statistical methods (e.g., control charts)

statistics

science of decision-making in the presence of uncertainty

stopping power

Absolute value of the derivative of the kinetic energy of a particle moving through matter, such as an alpha-particle or proton, with respect to the distance traveled; or the rate of energy loss per unit distance along the path. The stopping power depends on the type of particle, its energy, and the material through which the particle is moving; and changes as the particle slows down.

Student’s t-distribution

A type of probability distribution. If ν is a positive number, Z and W are independent random variables, Z has the standard normal distribution, and W has the chi-squared distribution with ν degrees of freedom, then the random variable T defined by

T =

Z √ W / ν

has Student’s t-distribution with ν degrees of freedom. When ν > 1, the mean of T is 0, and when ν > 2, the variance is ν / (ν − 2). As ν → ∞, the t-distribution converges to the standard normal distribution.

subsample

1. (noun) portion of a sample removed for testing
2. (verb) to remove a portion from a sample for testing

substance

(in the term amount of substance) collection of elementary entities (such as atoms or molecules) of a specified type (see also pure substance)

summing

absorption by a radiation detector of the energies from two or more coincident radiations, which appear as if they were a single radiation of higher energy

sum peak

peak in a radiation spectrum produced by summing

supernatant

liquid that overlies material deposited by settling or precipitation

supported

being replenished by ingrowth

surface barrier detector

radiation detector made from a wafer of either n-type or p-type silicon, to which a thin contact (e.g., metal evaporation or ion implant) of opposite type (e.g., p-type gold evaporation applied to n-type silicon) is applied to form a junction or diode

suspension

“A liquid in which solid particles are dispersed.” [IUPAC]

swipe

physical sample obtained by rubbing a clean filter pad over a specified surface, typically of about 100 cm², to test for removable contamination — also called smears or wipes

symbol of a unit (of measurement)

the symbol or abbreviation adopted by convention to designate a unit of measurement in expressions for values of quantities (e.g., m for meter, or ° for degree of plane angle).

Note 1: In text, a unit symbol ordinarily should appear only after a number. It should not appear alone in text as an abbreviation for the name of the unit where the name of the unit could be used instead.
Note 2: Generally there should be a space between the number and the unit symbol. The only exceptions to this rule allowed (and required) by the SI occur when one uses the symbols °, ′, and ′′ in expressions for plane angle, in which case there should be no spaces between the numbers and symbols. In all other cases, even when using the percent sign (%) or °C, the rule should be followed.
Note 3: The symbol for an SI unit should not be italicized or slanted, regardless of the format of the surrounding text.
Note 4: The symbol for an SI unit is not followed by a period except when required for reasons of grammar and punctuation (e.g., at the end of a sentence).
Note 5: The symbol for an SI unit has the same form for both singular and plural quantities.

systematic effect

recognizable effect on the result of a measure­ment pro­duced by an influence quantity (cf. random effect)

systematic error

“mean that would result from an infinite number of measurements of the same measurand carried out under repeatability conditions minus a true value of the measurand” [VIM]

Note 1: The systematic error of a measurement does not vary if the measurement is repeated under the same conditions of measurement (cf. random error). However, it may vary if the conditions change.
Note 2: The term “systematic error” is not a synonym for “Type B uncertainty.”

system of units (of measurement)

“set of base units, together with derived units, defined in accordance with given rules, for a given system of quantities” [VIM]