Epithelial tissue.

The cell types on the outer surface of mammalian tissues. Endothelia cell layers are on the inner surfaces of tissues. Cells in-between are mesothelial.

Equilibrium ratio (F).

The ratio of the potential alpha energy concentration of radon decay products to the concentration of radon. Under ideal conditions, when all of the radon decay products remain suspended in air, they reach equilibrium with radon and F approaches 1.0. In family dwellings, F is typically near 0.4.

Equilibrium-equivalent radon concentration (EEC).

The concentration of radon in equilibrium with the short-lived decay products that has the same potential alpha concentration as a given mixture of decay products.

Equivalent dose (H).

The product of absorbed dose, D, and a radiation weighting factor, wR, that depends on the type of radiation responsible for the dose. H = wR.D. The purpose is to account for the differences in biological response for different types of radiation. If dose is measured in Gy, H has units of Sievert (Sv). If D is measured in rad, H has units of rem.

Excess relative risk (ERR).

A model, which assumes that health effects from ionizing radiation are based on a relative risk factor, RR, that multiplies the baseline risk. Excess relative risk, ERR, is then defined formally as: RR-1.


A source of exposure that is outside the body.



Pertaining to, produced by, or formed in a stream or river.


Two oncogenes that interact as a dimer which binds to specific DNA control sequences regulating the transcription of genes. Fos/jun is particularly responsive to DNA damage and induces transcription of damage-responsive genes.

Fusion gene.

A gene produced by breakage and rejoining of DNA within gene sequences to produce a new gene with altered function. Bc12 is involved in a well-known fusion gene produced during some classes of hematopoetic cancer.


G1 and G2.

The periods in the cell cycle that are respectively before and after, the period of semiconservative DNA synthesis called the S phase. In the process of cell division, mitosis, follows the completion of G2. Most cells in somatic tissues are either in the G1 phase of the mitotic cycle, or are not in a mitotic cycle at all and are then classified as being in G0.

Gamma ray (γ).

A particle emitted during the decay of certain radioactive elements. It is a form of electromagnetic radiation also referred to as a photon. Gamma rays have energies usually between 10 kev and 10 MeV.

Genomic stability.

The concept where the genome of a normal diploid cell maintains a complement of maternal and paternal genes by specific mechanisms. These become deranged in malignant cells and can cause changes in gene copy number, chromosome numbers, heterozygosity, total DNA content, etc.

Geometric mean (GM).

The nth root of the product of n observations.

Geometric Standard Deviation (GSD).

The exponential of the standard deviation of the natural logarithms of a set of observations.

Granular activated carbon (GAC).

Organic matter such as wood, bone or coconut shells, that is exposed to high heat and pressure. This increases the surface area and improves the capability to adsorb contaminants.

Gray (gy).

A quantity of absorbed dose equal to 1 Joule kg-1. One Gy = 100 rad. The gray is a SI unit named on behalf of the British scientist L.H. Gray.

Groundwater disinfection rule (GWDR).

Pending rule proposed by USEPA that will require public drinking water supplies that use groundwater to disinfectant the drinking water prior to distribution.


Half-life (t1/2).

The amount of time required for a given quantity of radioactivity to be reduced by one half. This only includes the radioactive decay process and does not include removal radioactivity by other methods such as biological elimination or migration.


The lineage of cells in the bone marrow, spleen and thymus that produces the erythrocytes, lymphocytes, platelets and other cells of the peripheral blood.

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