Radioactivity measurement units

Facts and Information about Radiation Exposure The Energy Collective,

There are three measurement units for radioactivity: the becquerel (Bq) measures radioactivity, the gray (Gy) measures the absorbed dose and the Sievert (Sv) measures the biological effects of the absorbed dose.

The Bq measures the activity of the radioactive source, meaning the number of atoms which, within a particular time frame, transform and emit radiation.

1 Bq = 1 disintegration per second (dps); disintegration energy levels vary by isotope.

The Bq is a very small unit; multiples are often used:

1 MBq = 1 mega becquerel = 1,000,000 Bq

1 GBq = 1 giga becquerel = 1,000,000,000 Bq

1 TBq = 1 tera becquerel = 1,000,000,000,000 Bq

The radioactivity of an environment, a material or a foodstuff is given in Bq per kilogram or per liter.


The Gy measures the absorbed dose, meaning the energy transferred by one or more isotopes to the material by ionizing radiation upon encountering it.

1 Gy = 1 joule of ionizing energy per kilogram; Sub-multiples are often used:

1 mGy = 1 milligray = 0.001 Gy

1 uGy = 1 microgray = 0.000001 Gy

1 nGy = 1 nanogray = 0.000000001 Gy


The Sv evaluates the effects of ionizing radiation on living material. At equal Gy doses, the effects of radioactivity on living tissue depends on the type and energy level of the radiation (alpha, beta, gamma, neutron, etc.), on the tissue type and on the length of exposure.

The Sv is a very large unit; sub-multiples are often used:

1 mSv = 1 millisievert = 0.001 Sv

1 uSv = 1 microsievert = 0.000001 Sv



International System of units (SI Units) and corresponding Common Units

– Bq is the unit of radioactivity that corresponds to the curie (Ci)

– Gy = 1 joule/kg is the unit of Absorbed Dose that corresponds to the rad

– Sv = 1 J/kg x We x Wt is the unit of Equivalent Dose that corresponds to the rem

– coulomb/kilogram (C/kg) is the unit of exposure that corresponds to the roentgen (R)


1 Joule = 6,200 billion mega electronvolt (MeV) = 1 watt.second

kBq/sq m = 1,000 Bq of radioactive particulate over an area of 1 sq m

1 TBq = 27 Curies, or 1 pCi = 0.037 Bq

1 GBq = 27 mCi

1 MBq = 27 uCi

37 GBq = 1 Ci


1 rad = 0.01 Gy

1 rem = 0.01 Sv

1 roentgen (R) = 0.000258 coulomb/kilogram (C/kg)

1 coulomb = 1 amp.second; it is a flow of one amp of electric charge for one second.



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