µ GCSE | Half Life

10 quick questions - for GCSE


10 minutes maximum! (can you do it in 5?)

 1. Which of these is the best description of the 'activity' of a radioactive rock?

  • A. The total number of radioactive atoms that have decayed.
  • B. The total number of radioactive atoms remaining undecayed in the rock.
  • C. The number of gamma rays emmited per second.
  • D. The number of radioactive atoms that have decayed per second.


2. What are the units used to measure the Activity of a sample of rock?

  • A. coulombs (C)
  • B. becquerels (Bq)
  • C. joules (J)
  • D. watts (W)


The graphs below show 4 ways the count rate from a radioactive isotope could change:







3. Which of the above graphs shows the correct shape for radioactive decay?

4. Using the correct graph, what is the half life of the sample?

  • A. 5 years
  • B. 10 years
  • C. 20 years
  • D. 40 years

5. What is the activity of the sample after 2 half lifes?

  • A. 800 counts per second
  • B. 400 counts per second
  • C. 200 counts per second
  • D. 0 counts per second

6. Use the correct graph to estimate the count rate after 30 years.

  • A. 100 counts per second
  • B. 200 counts per second
  • C. 25 counts per second
  • D. 550 counts per second


Q7-10: An isotope has a half life of 8 hours.

7. How much of the sample will remain after 24 hours?

  • A. 12
  • B. 13
  • C. 14
  • D. 18

8. If the mass of the isotope is 12 g of pure radioactive isotope, how many grams remains after 16 hours?

  • A. 0.75 g
  • B. 3 g
  • C. 4 g
  • D. 6 g

9. What has happened to the rest of the mass of the isotope?

  • A. All converted to radiation
  • B. All converted to heat energy.
  • C. Converted into a new element.
  • D. remained the same isotope but evaporated.

10. Here are three suggestions for safe use for the isotope:

Which of these are realistic and sensible suggestions?

  • A. II only
  • B. I and II
  • C. II and III
  • D. All three


I. Do not handle directly - use tongs.

II. Store in a thick lead or steel box.

III. Do not look directly at the isotope whilst handling it.