R

Ra

atomic symbol for radium

rad

name and symbol for the traditional non-SI unit of absorbed dose, equal to 0.01 Gy

radiation

radiant energy emitted in the form of waves or particles (see also ionizing radiation)

Note: In the radio­chem­istry labo­ra­tory the term radiation is often used as a syno­nym for ioniz­ing radiation.

radiation counter

system that includes a radiation detector and asso­ciated elec­tronics for count­ing detected events

radiation counting

counting quanta of radiation (photons or particles) that impinge on and deposit energy in a radiation detector (see also radiation counter)

radiation detector

detector for radiation, especially ionizing radiation

radiation safety officer (RSO)

person responsible for manag­ing a labo­ra­tory’s radiation safety program

radioactive

1. exhibiting radioactivity
2. containing radionuclides
3. of or relating to radioactivity

radioactive decay

spontaneous transformation of one nuclide into one or more other nuclides, accompanied by the release of radiation

Note: There are differ­ences of opinion about what con­sti­tutes radio­active decay. Any unstable nucleus has a half-life and “decays,” and it releases energy some­how when it decays. How­ever, some authorities require a change in proton number or neutron number to call this process “radio­active decay.” So, for example, in their terminology iso­meric tran­si­tion is not a form of radio­active decay. Others have defined radio­active decay more generally so that it includes isomeric transition. My own pref­er­ence, for what it’s worth, based on my experience in a radio­chem­istry lab and help­ful argu­ments with colleagues, is to include any spon­taneous change from one nuclide to another, so that a meta­stable state that under­goes iso­meric tran­si­tion to reach the ground state is con­sidered to under­go radio­active decay, but an energy state that decays too quickly to be called a nuclide does not nec­es­sarily under­go radio­active decay. We want the word activity to mean the rate of radio­active decay, and it must apply to all radio­nuclides but not nec­es­sarily to short-lived energy states. (I’m not opposed to in­cluding all spon­taneous nuclear tran­si­tions in the defi­ni­tion, but that ques­tion seems un­important.)

radioactive equilibrium

condition that exists in a quantity of material when the ratios of the activities of radionuclides in a decay chain have approached limiting values and are no longer changing appreciably (see also secular equilibrium and transient equilibrium)

Note: Radioactive equilibrium may exist for all of the radio­nuclides in the decay chain or only for a subset.

(radioactive) source

quantity of material configured for use, observation, or measurement of the radiation it emits (see also calibration source, check source, and test source).

Note: In the radiochemistry labo­ra­tory a “radio­active source” may or may not actually be radioactive, but it is treated as potentially radioactive.

radioactivity

property, exhibited by certain nuclides, of under­going radio­active decay

radioanalysis; radioassay

measurement of radiation emitted from a radioactive source; radiation analysis

radioanalytical

of or relating to radioanalysis

radiochemical

of or relating to radiochemistry

radiochemical analysis

analysis of a sample or item for radioactive materials

radiochemist

practitioner of radiochemistry

radiochemistry

branch of chemistry that deals with radioactive materials

radioisotope

isotope (of an element) that exhibits radioactivity

radiological

of or relating to radiology

radiology

1. science of radioactive substances and high-energy radiations
2. branch of medicine which deals with the diagnostic and thera­peutic appli­ca­tions of radiant energy includ­ing x rays and radio­nuclides [RHH]

radiolysis

decomposition of a material as a result of exposure to radiation

radiometric

relating to measurement of or by radiation

radiometry

measurement of radiation, especially electro­magnetic radia­tion in or near the visible range

radionuclide

nuclide that exhibits radioactivity

radiotracer

radioactive tracer, measured by radioassay

random effect

effect on the result of a measurement produced by unpredictable or stochastic varia­tion of an influence quantity (cf. systematic effect)

random error

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

Note 1: The random error of a measurement varies if the measurement is repeated under the same conditions of measurement (cf. systematic error).
Note 2: The term “random error” is not a synonym for “Type A uncertainty.”

random summing

summing that occurs when two atoms happen to emit detectable radiations within a time period shorter than the resolving time of the detector

range (of a measurement method)

set of values of the measurand for which a specified measurement method is applicable, usually expressed as an inter­val from the mini­mum value to the maxi­mum value

range (of radiation)

distance through which radiation travels in a given medium or the dis­tance traveled before a specified interaction

range (of a set of values)

difference between the maximum and minimum of a set of values

Rb

atomic symbol for rubidium

Re

atomic symbol for rhenium

reagent blank

artificial sample prepared in the laboratory using only purified water and reagents and analyzed like a normal sample for the purpose of detect­ing or quantifying analytes that may be present in the reagents

real time

elapsed time between the beginning and end of a nuclear counting measurement (cf. live time)

recoil

movement of an atom away from the direction of radiation emitted during radioactive decay

recoil atom

portion of an atom remaining after emission of a photon or particle, which recoils in the direction opposite from that of the emission

recombination

in an ionization chamber, the capture of a free electron by a positive ion or the transfer of an electron from a negative ion to a positive ion, which eliminates one ion pair and thereby reduces the amplitude of the generated pulse

recovery

1. chemical yield
2. ratio of the result measured for a spiked sample or reference material to the amount, activity, or con­cen­tra­tion of analyte added, usually ex­pressed as a percentage

rectangular distribution

A random variable X has a rectangular distribution if there are real numbers, a₋ and a₊, such that a probability density function for X has a con­stant posi­tive value on the interval [a₋,a₊] and is zero elsewhere.

redox reaction

oxidation-reduction reaction

reduction

gain of one or more electrons by an atom in a chemical reaction, or a decrease in its positive valence (cf. oxidation)

reducing agent

1. in an oxidation-reduction reaction, the substance that loses electrons, or is oxidized
2. substance that readily donates electrons

reference material (RM)

“material or substance one or more of whose property values are suffi­ciently homo­geneous and well established to be used for the calibration of an apparatus, the assess­ment of a measure­ment method, or for assign­ing values to materials” [VIM] — see also certified reference material and standard reference material

region of interest (ROI)

range of channels (or energy interval) in a multi-channel analyzer designated for radiations of a particular type or energy

relative

The adjective relative is sometimes used with the name of a physical or mathematical quantity to indi­cate the quo­tient of that quantity and a related quantity, as in relative atomic mass, relative error, etc. (cf. absolute).

relative atomic mass (A_r)

(of an element or nuclide) ratio of the average mass per atom to the atomic mass constant — formerly called atomic weight

relative error

“error of measurement divided by a true value of the measurand” [VIM]

relative humidity

ratio of the partial pressure of water in the air to the saturation vapor pressure of pure water at the same temperature

Note: The relative humidity is dimensionless and is often expressed as a percentage.

relative molecular mass (M_r)

ratio of the average mass per molecule of a substance to the atomic mass constant — formerly called molecular weight

relative standard deviation (RSD)

coefficient of variation

relative standard uncertainty

standard uncertainty of the result of a measurement divided by the absolute value of the result

relative variance

square of the coefficient of variation of a nonnegative random variable, or the quotient of the variance and the square of the mean

rem

traditional non-SI unit of dose equivalent, equal to 0.01 Sv

repeatability

precision under repeatability conditions (see also entries for reproducibility below)

repeatability conditions

conditions of measurement that involve the same measurement procedure, measuring instruments, personnel, and location, and repetition of measurements within a short time frame (cf. reproducibility conditions).

replicate

any of two or more repeated measurements of one measurand made for the purpose of checking the precision of the measurement process (cf. duplicate)

representativeness (of a sample)

degree to which the properties of a sample match those of the lot or population it is taken to represent

Note: Representativeness, like accuracy, is a qualitative concept.

reproducibility (of results of measurements)

precision of results of measurements of the same measurand obtained under changed conditions of measurement [VIM]

Note: A useful statement of reproducibility requires a statement of the conditions changed, which may include the measurement procedure, measuring instruments, personnel, etc.

reproducibility (of a measurement procedure or measuring instrument)

precision of results of measurements of the same measurand obtained under reproducibility conditions

reproducibility conditions (for a measurement procedure)

conditions of measurement that involve the same measurand and measurement procedure but different measuring instruments, personnel, locations, and times

reproducibility conditions (for a measuring instrument)

conditions of measurement that involve the same measurand, measurement procedure, and measur­ing instru­ment but dif­fer­ent personnel and times, and if pos­sible, dif­fer­ent locations

resin

polymer used in ion-exchange chromatography to form the stationary phase, often produced in the form of small beads to increase the total surface area

resolution; peak resolution

sharpness of the peaks in a spectrum, usually described by the peak width (e.g., FWHM)

resolving time

minimum separation between two ionizing events required for a radiation detector to detect both as distinct events (cf. dead time)

result (of measurement)

“value attributed to a measurand, obtained by measurement” [VIM]

Rf

atomic symbol for rutherfordium

Rh

atomic symbol for rhodium

Rn

atomic symbol for radon

robustness

in general, the degree of insensitivity of a method or procedure (e.g., a statistical test) to violations of its assumptions

robustness (of a measurement method)

See ruggedness

röntgen; roentgen (R)

traditional non-SI unit of exposure, equal to 2.58 × 10⁻⁴ C/kg

R-qualifier

data validation qualifier applied to a test result to indicate that it is unusable (rejected). Colloquially called an R-flag

Note: The term R-flag may also be used as a transitive verb, meaning to apply an R-qualifier to.

Ru

atomic symbol for ruthenium

ruggedness

ability of a measurement method or procedure to give consistent results despite varia­tions in meas­ure­ment con­di­tions or influence quantities