appear to be equally effective in producing biological effects in a given organ of the body even though the radiations may not be equally effective. Special weighting factors (i.e., radiation weighting factors) are used to convert absorbed dose to equivalent dose. Other weighting factors are used to convert equivalent doses to effective dose, which is more often used in risk assessment. With effective dose, a single number applies to the total body. With equivalent dose, different doses may be attributed to different organs. The name is derived from the Swedish physicist, Rolf M.Sievert.

SI units

—the international system of units. Special SI units for radiation include the becquerel (Bq), gray (Gy), and sievert (Sv).

Standard deviation

—square root of the variance (see below).

Strontium-90

—a beta-emitting isotope of strontium which element is chemically similar to calcium. Strontium-90 has a half-life of 28 years, is a common isotope produced in nuclear reactors, and is contained in fallout from nuclear testing.


Threshold

—some minimal dose to a population required to produce a specified biological effect; below this dose the effect dose not occur among any member of the population. Biological effects requiring threshold radiation doses are called deterministic effects.

TOA

—time of arrival.


Uncertainty

—the term used to describe the lack of precise knowledge in a given estimate based on the amount and quality of the evidence or data available.

UNSCEAR

—the United Nations Scientific Committee on the Effects of Atomic Radiation, one of the specialized bodies of the United Nations charged with the responsibility of evaluating the effects of exposure to atomic (ionizing) radiation on behalf of the member nations.


Variance

—a measure of the spread or dispersion of a variable about its mean value. It is by definition the mean of the squared deviations of the values of the variable about their mean. The standard deviation is the square root of the variance.


X-rays

—High-energy lectromagnetic radiation with a wavelength that is much shorter than that of visible light, historically the rays produced in an electrical device, e.g., such as a diagnostic x-ray machine.


Yield

—the total effective energy released in a nuclear detonation and measured in tons of trinitrotoluene (TNT) equivalent.



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