Define radioactive activity and its relation to half-life for equal atom counts.

Solution & explanation

Activity is decays per second, in becquerels: 1 Bq = 1 s⁻¹. A = λN and λ = ln2/T½, so for equal N a shorter half-life means greater activity. Equal masses of different isotopes need not have equal atom counts; activity is not the same as absorbed dose.