Activity - Aetherwisp

Activity is the number of decays per unit time in a macroscopic sample of a radioactive object:

A(t)=\lambda N(t)=A_{0}e^{-\lambda t}\quad\text{with}\quad A_{0}=\lambda N_{0},

where $N(t)$ is the number of nuclei left at time $t$ (see Radioactive decay law) and $\lambda$ the decay constant.

Activity is measured in Becquerel: $1\text{ Bq}=1\text{ decays/s}$ . Historically the Curie was also used: $1\text{ Ci}=3.7\times10^{10}\text{ decays/s}$ , which is the activity of one gram of radium.