same as one Gy. The Sievert is an SI unit named on behalf of the Swedish scientist Rolf Sievert.

Signal transduction.

The chain of events that starts from initial damage, or from an intercellular signal peptide, and propagates through intervening molecules to eventually cause such events as apoptosis, changes in gene expression or cell cycle delays.


The cells of the adult body tissues, in contrast to germ cells which are involved in sperm and egg cell production.


Pertaining to or affecting the organs in the viscera, especially the intestines, and their associated blood vessels.

Stern cells.

The cells in a tissue that have indefinite potential for cell division, and divide relatively slowly. They serve as a source for most of the cells in a tissue and act as a reserve for repopulation following tissue damage.

Stochastic radiation injury.

Health effects from ionizing radiation that occur randomly where the probability of occurrence is proportional to absorbed dose with no apparent threshold.



An agent that tends to produce anomalies in developing embryos.


That division of embryology and pathology which deals with abnormal development and congenital anomalies.


The specific DNA sequences that form the ends of chromosomes and are replicated by specific enzyme systems, telomerase, which contain a polyribonucleotide sequence that acts as a template for telomere replication.


A value of absorbed dose below which the probability of a specific radiation induced health effect is zero.

Time-since-exposure (TSE) model.

A risk projection model in which the risk varies with the time after exposure.

Tissue weighting factor (wT).

The ratio of the risk for developing radiation induced cancer in a tissue, T, to the combined risk of developing cancer in any organ following a uniform irradiation of the whole body to the same equivalent dose.


Total organic carbon: sum of the particulate and dissolved organic matter in a sample such as water.


The process by which a gene sequence in DNA is used to synthesize a matching sequence of ribonucleic acid (RNA).

Transfer factor (T).

The average increment of the radon concentration in indoor air (a) divided by the average radon concentration in the water (w).


The process where a specific RNA sequence is used for the synthesis of a protein in which a code based on 3 bases read together (triplet code) specifies an amino acid position in the protein.

Trihalomethanes (THMs).

A class of potentially toxic chemical byproducts such as chloroform, dibromochloromethane, dichlorobromomethane, and bromo-form, that can be formed when water that contains natural organic matter is disinfected by the addition of chlorine.

Triplet repeats.

Regions of DNA in which a sequence of three nucleotides is repeated many times.



Upper confidence limit; the upper bound of a confidence interval.


A lack of knowledge concerning the truth. This can be quantitative or qualitative.



The variation of a property or a quantity among members of a population. Such variation is inherent in nature and thus unavoidable. It is often assumed to be random, and can be represented by a frequency distribution.

Volatile organic contaminants (VOCs).

Those organic compounds that are considered contaminants in air or water. The compounds usually transfer spontaneously from water to air.


Working level (WLM).

A quantity of potential alpha energy concentration equivalent to 2.08 × l0-5 J m-3.

Working level month (WLM).

An exposure to radon decay products suspended in air that is determined by PAEC multiplied by the residency time at that location. One WLM is equivalent to 1 WL for 170 hours which equals 12.7 J m-3 s.

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