The correct option is (B) A2 = A1e[{t(1) – t(2)} / T].
Explanation:
mean life time = T = (1 / λ) ......(1)
Activity after time t is A = A0e–λt where A0 = initial activity by given
condition, A1 = A0e–λt(1)
A2 = A0e–λt(2)
∴ Taking ratio (A2 / A1) = e–λt(2)+λt(1)
∴ A2 = A1e[t(1) –t(2)]λ
from (1) A2 = A1e[{t(1) –t(2)} / T].