The curie (Ci) was originally defined as the activity of what quantity of radium-226?

1. The curie is a historical unit of activity, distinct from the SI becquerel. 2. It was defined as the activity of exactly 1 gram of radium-226. 3. A kilogram or a mole of radium-226 would represent a much larger activity than one curie. 4. A single atom's decay rate is far too small to define a practical unit like the curie. 5. So 1 gram is correct. _Source: OpenStax Physics (CC BY 4.0), Ch 22 "The Atom", section 22.3 Half Life and Radiometric Dating_