In a radioactive material the activity at time is and at a later time , it is . If the decay constant of the material is , then
(a) The decay rate R of a radioactive material is the number of decays per seconds.
From radioactive decaylaw,
i.e. Rate of reaction is directly proportional to the initial concentration of reactants.
where is the activity of the radioactive material at time t=0.
At time ...(ii)
At time ...(iii)
Dividing Eq. (ii) by Eq. (iii), we have