What is the traditional unit of activity in radioactivity?

The traditional unit of activity in radioactivity is the Curie (Ci). This unit was named after Marie Curie and her husband Pierre Curie, who conducted pioneering research in radioactivity. One Curie is defined as the amount of radioactive material that decays at the rate of 3.7 x 10^10 disintegrations per second, which corresponds to the radioactivity of one gram of radium-226. The Curie has been widely used historically due to its clear linkage to the actual physical phenomena associated with radioactive decay.

If students encounter the Becquerel (Bq), it's worth noting this is the SI unit equivalent to the Curie but represents a modern standardization of radioactivity, defined as one disintegration per second. The Rad and the Gray are units of absorbed dose and are not measures of radioactivity or activity itself, further differentiating the context in which they are used.