Sv

Sv is the symbol for the sievert, the SI unit used to measure the biological effects of ionizing radiation. It quantifies dose equivalents that reflect the potential for stochastic health effects, such as cancer, rather than the physical energy deposited alone.

The sievert is a derived unit. The equivalent dose H_T for a tissue T is obtained by multiplying the absorbed dose D_T by a radiation weighting factor w_R that accounts for the quality of the radiation. The effective dose E is the sum over tissues of the tissue-weighted equivalent doses, using tissue-weighting factors w_T that reflect the varying radiosensitivity of different organs. In practice, for low-LET radiations like X-rays and gamma rays, 1 Sv of equivalent or effective dose roughly corresponds to 1 Gy of absorbed dose, but the factors adjust doses for different radiation types and tissue responses.

The sievert is named after Rolf Maximilian Sievert, a pioneer in radiation protection. It is a published SI unit and is widely used in radiation protection, medical imaging, and nuclear industry to assess risk rather than to measure energy deposition alone.

Common usage and limits: occupational exposure is typically limited to about 20 mSv per year, averaged over five years, with no more than 50 mSv in a single year. Public exposure limits are generally about 1 mSv per year above background and medical exposures. One sievert equals 1000 millisieverts.

Examples of typical levels: natural background radiation varies by location but is roughly 2–3 mSv per year globally; a chest X-ray is about 0.02 mSv, while a CT examination can range from 1 to several tens of millisieverts depending on the procedure.