Page 9: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Radiological Parameters

Appendix B: Glossary of terms and units, conversion factors, and acronyms


Absorbed dose:
Quantity of energy imparted by ionizing radiation to unit mass of matter such as tissue. Unit gray, symbol Gy. 1 Gy = 1 joule per kilogram. See also Table B-1 below.
A group of 15 elements with atomic numbers from 89 to 103 inclusive. All are radioactive, and they include thorium, uranium, plutonium, and americium.
The rate at which transformations occur in a radioactive substance. Unit becquerel, symbol Bq. 1 Bq = 1 transformation or disintegration per second. See also Table B-1 below.
Alpha particle:
A particle consisting of two protons and two neutrons.
See Activity.
Beta particle:
An electron emitted by the nucleus of a radionuclide. The electric charge may be positive, in which case the beta particle is called a positron.
Committed effective dose:
The effective dose that will be accumulated over a period of time following a single intake of radioactive material into the body. Standard periods of integration are 50 years for adults and 70 years for a lifetime exposure.
The process of spontaneous transformation of a radionuclide. The decrease in the activity of a radioactive substance.
Decay product:
A nuclide or radionuclide produced by decay. It may be formed directly from a radionuclide or as a result of a series of successive decays through several radionuclides.
General term for quantity of radiation. See Absorbed dose, Committed effective dose, Effective dose, Equivalent dose.
Dose coefficient:
The committed effective dose resulting from the inhalation or ingestion of 1 Bq of a given radionuclide. Unit sievert per becquerel, symbol Sv/Bq.
Effective dose:
The quantity obtained by multiplying the equivalent doses to various tissues and organs by the tissue weighting factor appropriate to each and summing the products. Unit sievert, symbol Sv.
Electron capture:
Nuclear decay in which a proton in the nucleus acquires an electron from the outer cloud of the atom's electrons. This converts the proton to a neutron, reducing the number of protons in the nucleus by one and the atomic number of the original element by one. Atomic mass number remains constant because the total number of protons and neutrons is unchanged.
Equivalent dose:
The quantity obtained by multiplying the absorbed dose by the appropriate radiation weighting factor to allow for the differing effectiveness of the various ionizing radiations in causing harm to tissue. Unit sievert, symbol Sv. See also Table B-1 below.
Gamma ray:
A discrete quantity of electromagnetic energy, without mass or charge.
See Absorbed dose.
The time taken for the activity of a radionuclide to lose half its value by decay. Symbol t½.
The process by which a neutral atom or molecule acquires or loses an electric charge. The production of ions.
Ionizing radiation:
Radiation that produces ionization in matter.
Latency period:
the time between the actual exposure to a carcinogen and the development of cancer.
Nuclear fission:
The process in which a nucleus splits into two or more nuclei and energy is released.
An unstable nuclide that emits ionizing radiation.
Risk factor:
The probability of fatal cancer or leukaemia per unit effective dose.
Secular equilibrium:
a situation in which the quantity of a radioactive isotope remains constant because its production rate (due, e.g., to decay of a parent isotope) is equal to its decay rate.
See Effective dose.
Table B-1. Relationship between old and new radiation units
Old unit Symbol
New unit Symbol Relationship
Activity curie Ci becquerel Bq 1 Ci = 3.7 × 1010 Bq
Absorbed dose
rad rad gray Gy 1 rad = 0.01 Gy
Equivalent dose rem rem sievert Sv 1 rem = 0.01 Sv
Table B-2: Conversion factors
Multiple Prefix Symbol
1012 tera T
109 giga G
106 mega M
103 kilo k
10-3 milli m
10-6 micro µ
10-9 nano n
10-12 pico p


American National Standards Institute
Canadian Deuterium Uranium class of fission reactor
Canadian Nuclear Safety Commission
dose coefficient
deoxyribonucleic acid
granular activated carbon
tritiated water
International Commission on Radiological Protection
International Organization for Standardization
lower limit of detection
maximum acceptable concentration
NSF International
organically bound tritium
Standards Council of Canada
International System of Units
total dissolved solids
United States Environmental Protection Agency
World Health Organization

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