Sievert (radiation dose)
The SI unit of effective dose, weighting absorbed radiation energy by radiation type and tissue sensitivity to estimate stochastic health risk; 1 Sv = 1 J/kg.
The sievert converts physical absorbed dose (gray, Gy = 1 J/kg) into a risk-related quantity. Equivalent dose applies a radiation weighting factor wR (1 for photons and electrons, 2 for protons, 20 for alpha particles, 2.5–20 for neutrons depending on energy); effective dose then sums over organs with tissue weighting factors wT (ICRP Publication 103, 2007).
Reference values:
- Average natural background: about 2.4 mSv per year worldwide (UNSCEAR), mostly from radon; 6–10 mSv or more in parts of Kerala, Ramsar or Cornwall.
- Chest X-ray 0.02–0.1 mSv; CT scan of the abdomen about 8–10 mSv; transatlantic flight about 0.05–0.1 mSv.
- Public dose limit from regulated practices: 1 mSv/yr; occupational limit 20 mSv/yr averaged over five years.
- Living near a nuclear plant: typically below 0.01 mSv/yr.
- Acute dose of 1 Sv causes radiation sickness; about 4–5 Sv is lethal to roughly half of those exposed without treatment.
Under the linear no-threshold model used for protection, risk of fatal cancer is about 5% per sievert. In mortality terms per TWh, nuclear power ranks among the safest sources, comparable to wind and solar (Markandya and Wilkinson 2007; Our World in Data).
Related terms
All terms →- Nuclear fission
The splitting of a heavy atomic nucleus such as uranium-235 or plutonium-239 into lighter nuclei after absorbing a neutron, releasing about 200 MeV of energy and further neutrons.
- Spent nuclear fuel
Fuel assemblies removed from a reactor after use, highly radioactive and thermally hot, containing uranium, plutonium, fission products and minor actinides.
- Nuclear fusion
The joining of light nuclei, such as deuterium and tritium, into a heavier nucleus, releasing energy; the process that powers the Sun and an experimental route to electricity.
- Joule (J)
The SI unit of energy, work and heat: the work done by a force of one newton over one metre, or one watt sustained for one second.