Absorbed dose is a measure of the amount of energy from an ionizing radiation deposited in a mass of some material. For reasons of safeguarding human health, gray is admitted as SI unit for adsorbed dose rather than joule/kilogram based on its definition.
Dose equivalent is reached by mutiplying the absorbed dose of specific types of radiation with the weighting factor. Equal doses of all types of ionizing radiation are not equally harmful. To account for this difference, appropriate weighting factors can be applied reflecting the different relative biological effects to get the equivalent dose. The SI unit of equivalent dose is sievert (symbol Sv).
Radioactivity is caused when atoms disintegrate, ejecting energetic particles. SI unit for radioactivity is becquerel (symbol Bq ). One becquerel is the radiation caused by one disintegration per second.
Radiation Exposure is ionizing radiation of X-ray and gamma rays. The SI unit for radiation exposure is coulomb per kilogram (symbol C/kg).