Becquerel (SI unit)

Dr Daniel J Bell et al.

The becquerel (symbol: Bq) is the SI unit of radioactivity and is defined as one nuclear disintegration per second 1; it officially replaced the curie, the unit in the superseded cgs system, in 1975.


One becquerel is a very small unit and is invariably used with a prefix, e.g. megabecquerel (MBq), gigabecquerel (GBq), terabecquerel (TBq) and, even petabecquerel (PBq) are all used.

As for all other eponymous SI units when the unit is written out in full it is not capitalized, but when shortened to its symbol it is capitalized.

History and etymology

The unit was proposed in 1975 by the International Commission on Radiation Units and Measurements (ICRU). It is named after Antoine Henri Becquerel, the French physicist, who discovered radioactivity, and shared the Nobel Prize for Physics in 1903 with Marie Skłodowska-Curie and Pierre Curie 1,2. Ironically the former unit that the becquerel replaced was the curie!

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Article information

rID: 57178
Section: Physics
Synonyms or Alternate Spellings:
  • Becquerels
  • Petabecquerel (PBq)
  • Terabecquerel (TBq)
  • Gigabecquerel (GBq)
  • Megabecquerel (MBq)
  • Bq (unit)
  • Bq

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