Sievert Sievert The sievert (symbol: Sv) is a derived unit of ionizing radiation dose in the International System of Units (SI) and is a measure of the health effect of low levels of ionizing radiation on the human body. The sievert is of importance in dosimetry and radiation protection, and is named after Rolf Maximilian Sievert, a Swedish medical physicist renowned for work on radiation dose measurement and research into the biological effects of radiation. The sievert is used for radiation dose quantities such as equivalent dose and effective dose, which represent the risk of external radiation from sources outside the
Ionizing radiation radiation is always ionizing, but only extreme-ultraviolet radiation can be considered ionizing under all definitions. As noted, the biological effect of ionizing radiation on cells somewhat resembles that of a broader spectrum of molecularly damaging radiation, which overlaps ionizing radiation and extends beyond, to somewhat lower energies into all regions of UV and sometimes visible light in some systems (such as photosynthetic systems in leaves). Although DNA is always susceptible to damage by ionizing radiation, the DNA molecule may also be damaged by radiation with enough energy to excite certain molecular bonds to form thymine dimers. This energy may be