1. State the meaning of the term ‘half-life’.

2. The activity of a radioactive sample decreases from 4000 counts per minute (c.p.m.) to 125 c.p.m. over a period of 40 minutes. Calculate the half-life of the source?

3. A radioactive source has a half-life of 8 hours. If the source has an initial activity of 32000 Bq, find its activity after 2 days.

4. A radioactive sample has a half life of 2 days. Calculate the time it will take for its activity to drop to one sixteenth of its original value.

5. A radioactive isotope has a half-life of 15 hours. 256 g of the isotope is placed in a sealed container. What mass of the isotope will remain radioactive after
60 hours?

6. A radioactive isotope contains 640 million atoms of the isotope. How many isotope atom s will remain after 6 half-lives have passed?

7. A radioactive rock with a half life of 8000 years has an activity of 20 MBq. What will be the activity after 40000 years?

8. A radioactive tracer is delivered to a hospital. If it has an initial activity of 2000Bq and decays to 250Bq in 36 minutes, calculate the half life of the tracer.

9. A radioactive source has a half life of 2 minutes. If it decays for 20 minutes and it’s final activity is 3Bq- what was it’s in intial activity?

10. The initial activity of a source is 240 cpm and it has a half life of 3 days. What will its final count be , if it decays for 12 days?