A radioactive isotope is being produced at a constant rate A. The isotope has a half life T. Initially, there are no nuclei and after a time, t>>T, the number of nuclei becomes a constant. The value of this constant is:
ATIn(2)
dNdt=A−λN
After time t >> T, the number of nuclei becomes a constant, so net rate of change in the number of nuclei, dNdt=0
which gives, N=Aλ
Substituting λ=ln(2)T, we get ATIn(2)