Eduprobe
Question:
A sample of radioactive material A, that has an activity of 10 mCi (1 Ci = 3.7 × 10¹⁰ decays/s), has twice the number of nuclei as another sample of a different radioactive material B which has an activity of 20 mCi. The correct choices for half-life of A and B would then be respectively:
10 days and 20 days
10 days and 40 days
20 days and 5 days
5 days and 10 days
Solution:
The correct option is A 20 days and 5 days
Activity A = λN
For A: 10 = (2N₀)λA
For B: 20 = N₀λB
∴ λB = 4λA ⇒ (T₁/₂)A = 4(T₁/₂)B