1. Two nuclei P,Q have equal number of atoms at t=0. Their half lives are 3 hours and 9 hours respectively. Compare their rates of disintegration after 18 hours. (Rp:RQ)
2. Obtain the amount of 27Co60 necessary to provide a radioactive source of 8.0 mCi strength. The half-life of Co is 5.3 years.
3. Half- life of 92u238 against α-decay is 4.5x109 years. Calculate the activity of 1 g sample of uranium. (Avogadro’s number=6x1026 atoms/kmol)
4. A radioactive isotope of silver has half life of 20 minutes. The fraction of the original activity that remain after one hour is _______________.
5. Starting with a sample of pure Cu66 , 7/8 of it decay into Zn in 15 minutes. The corresponding
half life is
6. A radioactive isotope has a half-life of T years. How long will it take the activity to reduce to 1% of its original value?
7. A radioactive sample has activity of 10,000 disintegrations per second (dps) after 20 hours. After next 10 hours its activity reduces to 5,000 dps. Find out its half life and initial activity.
8. The half-life of 38Sr90 is 28 years. What is the disintegration rate of 15 mg of this isotope?
9. In a given sample, two radioisotopes, A and B, are initially present in the ratio of 1:4. The half lives of A and B are respectively 100 years and 50 years. Find the time after which the amounts of A and B become equal.
10. Activity of a radioactive sample decrease to 1/3 of its original value in 3 days, then in 9 days its activity will becomes