Curie (unit)

Andrew Murphy and Dr Daniel J Bell et al.

The curie (symbol Ci) was the unit for radioactive decay in the cgs system. One curie was defined as the radioactivity of one gram of pure radium-226; this is equivalent to 3.7 x 1010 decays per second. It was officially replaced by the becquerel in 1975. 


One curie was too large to be useful for most everyday applications and therefore the millicurie (mCi) and even the nanocurie (nCi) were regularly employed; 1 nCi still represented 37 disintegrations per second or 37 Bq.

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

History and etymology

The curie is named after Marie Curie (1867-1934) and Pierre Curie, French physicists, who performed much of the early fundamental work on radioactivity. 

Imaging Physics
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Article information

rID: 58618
Synonyms or Alternate Spellings:
  • Curie (Ci)
  • nanocurie (unit)
  • microcurie (unit)
  • millicurie (unit)
  • nCi (unit)
  • μCi (unit)
  • mCi (unit)
  • Ci (unit)

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