The rate of disintegration of a sample of a radioactive element is called its activity. Let A denote the activity at time t and A0 the initial activity. Then,
The SI unit of activity is called the becquerel (Bq) in honour of Henri Becquerel. 1 Bq = 1 disintegration per second.
The earlier unit, the curie (Ci) was based on the activity of 1 gram of 226Ra.
1 Ci = 3.7 × 1010 Bqn It was named after Marie Curie, Polish-bom French chemist.
[Note : Eqn (1) is also written in the form A (t) = A0e-λt ]
