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Glossary - S


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Sabot

A lightweight carrier designed to center a smaller caliber projectile in a larger gun barrel. When the sabot round is fired, the sabot is normally discarded a short distance from the muzzle.

Short-Term Exposure Limit (STEL)

The maximum concentration to which workers can be exposed for up to 15 minutes continually. No more than four excursions are allowed per day, and there must be at least 60 minutes between exposure periods. The daily TLV®-TWA (time-weighted average) cannot be exceeded.

SI Units

The International System of Units as defined by the General Conference of Weights and Measures in 1960. The units are generally based on the meter/kilogram/second units, with special quantities for radiation including the becquerel, Gray, and sievert.

Sievert (Sv)

The international unit of dose equivalent. The dose equivalent in sieverts is equal to the absorbed dose in grays (see gray above) multiplied by the radiation weighting factor and tissue weighting factors. One Sv = 100 rem.

Sister Chromatid Exchange (SCE)

Damage to the genetic material of a cell where chromosomes break then rejoin improperly, often used to indicate whether something is harmful to genes.

Solubility

The capability of being dissolved in a fluid, such as body fluids.

Specific Activity

The activity of the radionuclide per unit mass of the material that contains the radionuclide. [For DU the specific activity is about 0.4 µCi/g.)

Stochastic Effect

A health effect that occurs randomly and for which the probability of the effect occurring, rather than its severity, is assumed to be a linear function of dose, with no threshold. In other words, the probability of the effect occurring is zero, only when the dose is zero. Incremental increases in dose will cause proportional increases in the probability of the effect occurring. Hereditary effects and cancer incidence are examples of stochastic effects. Also called non-deterministic.

Strafe

Attack by machine gun or cannon fired from an aircraft.

Subtle Perturbations

Medical testing is expected to yield results which are either normal or abnormal. The truth is that "normal" is usually a range. When testing is done on a group of people in a research project, there may be clustering of results at the high or low end of normal, at times including results which are just below or above the low and high normal cutoffs. When this occurs and there is no ready explanation, the results are called subtle perturbations.