(Sv) The sievert is the SI unit of a dose equivalent, which accounts for relative sensitivities of different tissues and organs exposed to radiation. The effective dose, usually measured in millisievert (mSv), attempts to reflect the biological effects of radiation. One sievert equals an ionizing x-ray or gamma radiation energy loss of 1 joule per kilogram of body tissue (1 gray). One sievert is equivalent to 100 rem.
It is named after Rolf Sievert, a Swedish medical physicist.

(Bq) Becquerel is the system international (SI) since 1985 new unit of radioactivity. 1 becquerel is equal to 1 disintegration per second.
1 Bq = 0.027 x10^-9 Ci (Curie).
In medicine and radiation protection the SI measurement units of becquerel, gray and sievert (should) have replaced the conventional units of curie, rad and rem.

To convert:


See also Gray, Sievert, Roentgen Equivalent In Man, Radiation Absorbed Dose, Count and Becquerel Antoine Henri.

Natural background radiation originates from radioactive elements in the environment, including food, water, soil and rock (also building materials), the atmosphere and cosmic rays. The level of natural exposure to radiation can vary greatly between different locations. In the US, the average annual exposure from natural sources to humans is about 3 mSv (millisievert) corresponding to 0.3 rem. Radon gas accounts for two-thirds of this exposure.
Background radiation may also interfere with measurements. Background radiation includes radioactive contamination of samples or incomplete absorption of radiation in a detector.

The deep dose equivalent is related to the dose in tissue at a depth of one centimeter due to external radiation. Also called personnel dose equivalent at a depth of 1 cm. The unit for deep dose equivalent is J/kg or sievert (Sv).

The directional dose equivalent is the equivalent dose at a point in a radiation field that would be produced by the corresponding expanded field at depth on a radius in a specified direction. The unit of directional dose equivalent in the SI system of units is joule per kilogram (J/kg) and sievert (Sv).