Sievert Nuclear Regulatory Commission permits the use of the units curie, rad, and rem alongside SI units, the European Union European units of measurement directives required that their use for "public health ... purposes" be phased out by 31 December 1985. An older unit for the dose equivalent is the rem, still often used in the United States. One sievert is equal to 100 rem: 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
Ionizing radiation nuclei, they are also sometimes written as or indicating a Helium ion with a +2 charge (missing its two electrons). If the ion gains electrons from its environment, the alpha particle can be written as a normal (electrically neutral) helium atom . Alpha particles are a hugely ionizing form of particle radiation. When they result from radioactive alpha decay they have low penetration depth. In this case they can be absorbed by a few centimeters of air, or by the skin. More powerful, long range alpha particles from ternary fission are three times as energetic, and penetrate proportionately farther in