Units of Radioactivity

Since the rate of radioactive decay is expressed in disintegrations per second (dps), two named units are commonly used to state it in practice.

The curie (Ci) is the older, historically defined unit, set equal to $3.7 \times 10^{10}$ dps (originally chosen to match the activity of one gram of radium-226). The becquerel (Bq) is the modern SI unit, simply defined as exactly $1\ \text{Bq} = 1$ dps -- a much smaller, more directly interpretable unit than the curie. …