C

C

atomic symbol for carbon

Ca

atomic symbol for calcium

calibration

“set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument or measuring system, or values represented by a material measure or a reference material, and the cor­respond­ing values realized by standards” [VIM]

calibration source

radioactive source prepared for the purpose of calibrating a radiation counter

carrier

“substance which, when associated in an appreciable amount with a trace of another substance, will carry the trace with it through a chemical or physical process” [ISO 921]

cascade summing

summing produced when two or more detectable radiations are emitted by the same atom within a period of time that is shorter than the resolving time of the detector (cf. random summing)

Example: When an atom of ⁶⁰Co undergoes beta decay, it also emits two gamma-rays in quick succession, one at 1173 keV and another at 1332 keV. The average time between the two gamma-rays is so short that they may register as a single event at 2505 keV.

cation

positively charged ion (cf. anion)

Cd

atomic symbol for cadmium

Ce

atomic symbol for cerium

Celsius temperature

difference between the thermodynamic temperature and 273.15 K (the stand­ard freez­ing point of water)

The SI unit of Celsius temperature is the degree Celsius (°C), which is equal in magnitude to the kelvin (K).

Čerenkov counting

radiation counting technique based on detection of Čerenkov radiation, generally using a photo­multiplier tube

Čerenkov radiation

electromagnetic radiation emitted by charged particles moving through a material at a speed greater than the speed of light in that material

certified reference material (CRM)

“Reference material, accompanied by a certificate, one or more of whose property values are certified by a procedure which establishes traceability to an accurate realization of the unit in which the property values are expressed, and for which each certified value is accompanied by an uncertainty at a stated level of confidence” [VIM and ISO Guide 30, which include additional notes]

Cf

atomic symbol for californium

channel

any of the data registers or memory locations in a multichannel analyzer used to record pulses

chain of custody (COC)

“an unbroken trail of accountability that ensures the physical security of samples, data, and records.” [EPA QA/G-8]

check source

radioactive source used to check the response of a radiation counter for quality control purposes

chemical analysis

analysis of a sample or item to identify or quantify its chemical components or to determine their structure

chemical recovery

chemical yield

chemical yield

fraction of the amount of a given element or compound remaining after specified chemical separations

Note: The chemical yield for a radiochemical analysis may be measured gravimetrically using a carrier or radiometrically using a radiotracer. The chemical yield is often called simply the yield.

chemiluminescence

luminescence produced by chemical processes

chi-squared (χ²) distribution (also “chi-square”)

the probability distribution of the sum of the squares of a finite collection of independent random variables, each of which has the standard normal distribution

If Z₁, Z₂, …, Z_N are independent and have the standard normal distribution (i.e., are normally distributed with mean 0 and variance 1), then the random variable X defined by

X = Z₁² + Z₂² + ^… + Z_N²

has the chi-squared distribution with N degrees of freedom. In this case the mean of X is N and the variance is 2N.

chromatography

physical method of separation in which the components to be separated are distributed between two phases, one of which is stationary (the stationary phase) while the other (the mobile phase) moves in a definite direction [IUPAC]

Cl

atomic symbol for chlorine

clock time

real time

Cm

atomic symbol for curium

Co

atomic symbol for cobalt

coefficient of variation (CV)

for a nonnegative random variable, the standard deviation divided by the mean — also called the relative standard deviation

coherent system of units (of measurement)

“system of units of measurement in which all of the derived units are coherent” [VIM]

coherent (derived) unit (of measurement)

“derived unit of measurement that may be expressed as a product of powers of base units with the proportionality factor one” [VIM]

coincidence counting

radiometric counting technique that lowers inter­fer­ence levels by reject­ing any event that is not accom­panied by one or more events occur­ring with­in a speci­fied time interval (cf. anticoincidence counting)

coincidence summing (or true coincidence summing)

cascade summing

cold finger

metal rod attached to a high-purity germanium or lithium-drifted germanium detector and immersed in a dewar of liquid nitrogen for the purpose of maintaining a cryogenic temperature in the germanium crystal

collector

the person who collects a physical sample

collection

sampling

colloid

1. colloidal suspension
2. material subdivided at a colloidal scale, occurring in a colloidal suspension

colloidal

involving a state of subdivision of a solid or liquid into particles or droplets with diameters roughly in the range from 1 nm to 1 μm

colloidal suspension

suspension in which the size of the particles lies in the colloidal range [IUPAC]

Note: Colloidal particles in a colloidal suspension generally do not settle out of the mixture spontaneously.

column

(in chromatography) “The tube and the stationary phase contained within, through which the mobile phase passes.” [IUPAC]

combined standard uncertainty

standard uncertainty of an output estimate obtained by propagating the standard uncertainties and estimated covariances of the input estimates

Note: The combined standard uncertainty of a result y is denoted by u_c(y).

combined variance

square of the combined standard uncertainty

Note: The combined variance of a result y is denoted by u_c²(y).

component (of combined standard uncertainty)

Given a measurement function, Y = f(X₁,X₂,…,X_N), the component of the combined standard uncertainty, u_c(y), generated by the standard uncertainty of an input estimate x_i equals the product of the standard uncertainty u(x_i) and the absolute value of the sensitivity coefficient, ∂f / ∂x_i. This component may be denoted by u_i(y).

component of combined variance

square of a component of combined standard uncertainty, which may be denoted by u_i²(y)

compound

pure substance that can be decomposed by chemical means (cf. element)

Compton baseline

baseline in a gamma-ray spectrum, which is produced largely by Compton scattering but also partly by tailing and other effects

Compton edge

feature of a gamma-ray spectrum which appears as an abrupt decrease in the slope of the baseline at the upper end of the energy distribution of the Compton electrons associated with a gamma-ray photopeak

Note: The Compton edge is found at the energy E_γ² / (E_γ + m_ec²/2), where E_γ denotes the energy of the photopeak.

Compton effect

partial transfer of the energy and momentum of a photon to a free or weakly bound electron, which results in an energetic free electron and a scattered lower-energy photon

Compton electron

the electron to which a photon imparts energy in the Compton effect

Compton photon

the lower-energy photon that emerges after an incident photon interacts with an electron by the Compton effect

Compton scattering

scattering of a photon by the Compton effect

concentration

1. quotient of a quantity and the associated volume, as in amount-of-substance concentration
2. quotient of a quantity and the associated size (volume, mass, etc.)

Note: Definition 1 is consistent with the definitions given in ISO 31-0, Quantities and units — General principles, and ISO 31-9, Quantities and units — Atomic and nuclear physics. However, radiochemists often use the term more generally, as in definition 2.

constitutional heterogeneity

heterogeneity of a material lot due to differences in the compositions of the fragments that constitute the lot, not to their spatial arrangement

Note: The constitutional heterogeneity of a lot is unaffected by mixing.

control

See statistical control. (See also in control and out of control.)

control chart

graph of observed values from a process used to monitor the stability of the process and to determine whether it remains in statistical control

control limit

values on a control chart that define the permissible bounds for the monitored quantity

Note: Control limits are action limits, which means that when the monitored quantity exceeds the control limits, action must be taken to investigate and possibly correct the situation.

conversion electron

electron ejected from an electron shell during internal conversion

coprecipitation

simultaneous precipitation of a normally soluble component with a macro-component from the same solution by the formation of mixed crystals, by adsorption, occlusion or mechanical entrapment [IUPAC]

correct sampling

According to Dr. Pierre Gy, sampling is correct if every fragment of material in the lot has the same probability of being selected for the sample. In most situations, the use of correct sampling ensures that the sampling bias is negligible.

correction

“value added algebraically to the uncorrected result of a measurement to compensate for systematic error” [VIM]

correction factor

“numerical factor by which the uncorrected result of a measurement is multiplied to compensate for systematic error” [VIM]

Note: Newer drafts of the VIM have generalized the definition of correction and removed the clear distinction between a correction and a correction factor. According to the draft definitions, any adjustment of the measurement result to compensate for systematic error is a correction.

corrective action

steps taken to correct a problem or deficiency in the laboratory and to prevent its recurrence

corrective action report

formal report of a problem or deficiency in the laboratory and the associated corrective action

correlation coefficient

covariance of two random variables divided by the product of their standard deviations (see also estimated correlation coefficient)

Note: The correlation coefficient is a real number between −1 and +1, inclusive.

cosmic radiation

radiation from outside the Earth’s atmosphere

cosmogenic radionuclide

radionuclide produced by bombardment of a stable nuclide by cosmic radiation (e.g., ¹⁴C or ⁷Be)

count

1. a single pulse processed during a counting measurement
2. total number of pulses recorded during a counting measurement

counter

See radiation counter

counting

See radiation counting

counting efficiency

detection efficiency

counting error

counting uncertainty

Counting error is the traditional term for this concept among radiochemists.

counting statistics

the statistics of counting random events, and in particular the statistics of radiation counting, especially when modeled by a binomial or Poisson distribution

counting uncertainty

component of the combined standard uncertainty (e.g., in a radiochemical measurement) produced by the randomness of radioactive decay, radiation emission, and radiation counting

count rate

quotient of the number of pulses recorded during a radiation counting measurement and the live time

Note: If the count rate is corrected by subtracting a background or blank value, it is called a net count rate. The uncorrected rate may be called the gross count rate.

counts per minute (cpm)

non-SI unit for count rate, equal to 1 min⁻¹ — never used with SI prefixes

counts per second

unit for count rate, equal to 1 s⁻¹

Note: The SI symbol for this unit is s⁻¹. The symbol “cps”, which has often been used, is not accepted for use with the SI.

count time

duration of a radiation counting measurement, which may refer to either real time or live time but more often to live time

covariance

measure of association between two random variables, X and Y, often denoted by Cov(X,Y) or σ_X,Y, defined as the expectation of the products of the deviations of X and Y from their respective means, i.e., Cov(X,Y) = E((X − μ_X)(Y − μ_Y)) (see also estimated covariance)

coverage factor (k)

numerical factor by which the combined standard uncertainty of the result of a measurement is multiplied to produce the expanded uncertainty

coverage interval

interval described by the result of a measurement and its expanded uncertainty, and intended to contain the value of the measurand with a specified high probability — may also be called uncertainty interval

Note: A coverage interval is frequently but incorrectly called a confidence interval. It typically does not meet the theoretical requirements for a statistical confidence interval.

coverage probability (p)

approximate probability that a specified interval about the result of a measurement contains the value of the measurand (also called level of confidence)

Note: The value of the measurand is considered to be a constant. The result and the endpoints of the interval are considered to be random variables because of the manner in which they are determined.

Cr

atomic symbol for chromium

critical level

traditional term for critical value (2) in the context of radionuclide detection

critical region

set of values for the statistic in a statistical hypothesis test that lead to rejection of the null hypothesis

critical value

1. in a statistical hypothesis test, a limiting value of the critical region
2. value that a measured result (e.g., for the gross or net instrument signal) must exceed to lead to the decision that the analyte is present

cross-contamination

contamination of one laboratory sample or portion thereof by material from another

cross section

A measure of the probability of a specified type of interaction between a photon or a moving particle such as a neutron, and another target particle, such as an atomic nucleus. In theory the cross section equals the integrated probability for the interaction over an infinite plane perpendicular to the direction of motion of the incoming photon or particle. Conceptually it may be thought of as the effective cross-sectional area the target particle presents to the incoming photon or particle. The cross section has the dimension of an area and is often expressed in barns.

crosstalk

1. detection of radiation emitted from one radioactive source by a detector configured to detect radiation emitted from a different source, which may occur as a result of inadequate shielding
2. misclassification by a radiation counter of radiations of one type as radiations of another type; e.g., misclassification of alpha-particles as beta-particles or vice versa by a gas proportional counter

Cs

atomic symbol for cesium

Cu

atomic symbol for copper

cumulative distribution function (cdf)

for a random variable, X, the function F that maps each real number x to the probability Pr(X ≤ x) — also called simply the distribution function

curie (Ci)

traditional non-SI unit of activity, equal to 3.7 × 10¹⁰ Bq, which is approximately the activity of one gram of pure ²²⁶Ra

Note: The curie is such a large unit that the picocurie (symbol pCi) is more com­monly used to express results of analyses of environ­mental samples. 1 pCi = 0.037 Bq.