Radiation Quantities and Units
Activity (or radioactivity) is a measure of the amount of radioactive material based on the number of radioactive decays occurring per second. The unit is the becquerel (Bq). 1 Bq is on decay per second.
Radiation is energy in motion, in the form of moving waves or particles. It is emitted from radioactive material.
Radiation Dose is a measure of the amount of exposure to radiation. The basic units are the gray (Gy) and the sievert (Sv).
The International System of Units (SI) defines prefixes to scale base units. Prefixes are used to avoid very large or very small numerical values. The chart below lists some of the commonly used SI prefixes.
Prefix Name  Prefix Symbol  Scientific Notation  Factor 





























In more detail
Dose rate is the quantity of radiation dose that is absorbed per unit time. This can be expressed in various ways, such as millisieverts per year (mSv/y), which is the dose (in millisieverts) that is absorbed in one year. Another common scale is μSv/h, which is the dose (in microsieverts) that is absorbed in one hour.
Kerma is an acronym for “kinetic energy released per unit mass” and has units of gray (Gy).
Fluence (or particle fluence) is the number of particles incident per area and has units of per square meter (m^{2})