Sievertiä

Sievertiä (symbol Sv) on the SI unit of dose equivalent and effective dose used in radiological protection. It expresses the potential biological effect of ionizing radiation on human tissue, rather than the purely deposited energy.

The absorbed dose is measured in gray (Gy), but the dose expressed in sieverts accounts for the type of radiation and the sensitivity of tissues. The equivalent dose for a tissue T is defined as the absorbed dose D in that tissue multiplied by the radiation weighting factor wR (H_T = D × wR). The effective dose is the sum over all tissues of each tissue’s equivalent dose weighted by tissue weighting factors wT. The result is expressed in sieverts.

Common magnitudes: 1 Sv equals 1000 millisieverts (mSv); 1 mSv equals 1000 microsieverts (µSv). Most natural background radiation is a few mSv per year; medical imaging can range from a fraction to several tens of mSv per procedure; occupational exposure limits are typically around 20 mSv per year, averaged over five years, with higher possible values in a single year under certain regulations.

Name and origin: The unit is named after Rolf Maximilian Sievert, a Swedish physicist who made foundational contributions to radiobiology and protection standards. The concept is distinct from the gray, the absorbed-dose unit; 1 Gy equals the energy deposited per kilogram, while the sievert applies weighting factors to reflect biological effects.

Finnish usage: In Finnish, the form sievertiä is used to denote multiple sieverts in partitive or plural contexts, for example in phrases like “kymmeniä sievertiä.”