Becquerel and Curie
Definition
The becquerel (Bq) is one nuclear disintegration per second, the SI unit of activity. The older curie (Ci) is 3.7 × 10^10 Bq, originally defined as the activity of one gram of radium-226. A typical microcurie radioisotope source used in a teaching demonstration is 37 kBq. A radiocarbon-active modern carbon sample sits at about 0.23 Bq per gram of carbon, which is where the counting challenge starts.
- Becquerel (Bq)
- 1 disintegration per second, SI unit
- Curie (Ci)
- 3.7 x 10^10 Bq
- Curie origin
- Activity of one gram of radium-226
- Modern carbon activity
- About 0.23 Bq per gram of carbon
Common questions
Why does forensic radiochemistry still encounter the curie despite Bq being the SI unit?+
Older instrumentation, legacy source certificates, and some national regulatory frameworks still label activity in curies or millicuries, so an analyst working with archived sources or older documentation needs to convert between the two units accurately.
Why is the low activity of natural carbon a challenge for radiocarbon work?+
At roughly 0.23 Bq per gram, a modern carbon sample produces very few decay events per unit time, which means counting statistics, background shielding, and long count durations, or an alternative method such as accelerator mass spectrometry, all become necessary to get a precise age estimate.
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