Curie

For other uses, see Curie (disambiguation).

The curie (symbol Ci) is a non-SI unit of radioactivity, defined as

1 Ci = 3.7 × 10¹⁰ decays per second.

Its continued use is discouraged.

This is roughly the activity of 1 gram of the radium isotope ²²⁶Ra, a substance studied by the pioneers of radiology, Marie and Pierre Curie, for whom the unit was named. In addition to the curie, activity can be measured using an SI derived unit, the becquerel (Bq), which equates to one decay per second. Therefore:

1 Ci = 3.7 × 10¹⁰ Bq = 37 GBq

and

1 Bq ≅ 2.703 × 10⁻¹¹ Ci

A radiotherapy machine may have roughly 1000 Ci of a radioisotope such as caesium-137 or cobalt-60. This quantity of radioactivity can produce serious health effects with only a few minutes of close-range, un-shielded exposure.

Another commonly used measure of radioactivity is the microcurie:

1 μCi = 3.7 × 10⁴ disintegrations per second = 2.22 × 10⁶ disintegrations per minute

The typical human body contains roughly 0.1 μCi of naturally occurring potassium-40.

See also

• Ionizing radiation
• United Nations Scientific Committee on the Effects of Atomic Radiation
• Radiation exposure
• Radiation poisoning
• Geiger counter