SP6g Half-Life

1. Which of the following is not a definition of radioactive half-life?

• The time it takes for the activity of a radioactive sample to fall by half
• Exactly half the time it takes for all the radioactive nuclei to decay
• The time you would have to wait for exactly 50% of the radioactive nuclei to remain un-decayed
• The time it takes for the number of nuclei of a radioactive isotope in a sample to halve

2. What fraction of a radioactive sample will remain after 1 half-life?

• 1/2
• 1/4
• 1/8
• 1/16

3. What fraction of a radioactive sample will remain after 2 half-lifes?

• 1/2
• 1/4
• 1/8
• 1/16

4. What fraction of a radioactive sample will remain after 3 half-lifes?

• 1/2
• 1/4
• 1/8
• 1/16

5. What will the count be after 2 weeks if the initial count is 1200 Bq and the isotope has a half life of hours of 7 days

• 1200 Bq
• 900 Bq
• 600 Bq
• 300 Bq

6. What mass will remain after 8 hours of 160 mg of a radioactive isotope with a half life of 2 hours?

• 16 mg
• 10 mg
• 80 mg
• 5 mg

7. The activity of a radioactive sample fell from 120 Bq to 30 Bq in 30 minutes. Calculate its half life

• 2 hours
• 1 hour
• 1.5 hours
• 15 minutes

8. The activity of a radioactive sample fell from 300 Bq to 75 Bq in 3 hours. Calculate its half life

• 2 hours
• 9 hours
• 90 minutes
• 30 minutes

9. A fragment of bone is discovered during an archaeological dig. The bone contains carbon-14 isotopes of the element carbon. The bone is approximately 23 000 years old. Calculate what proportion of the carbon-14 isotopes remains. Give your answer to the nearest whole fraction. The half-life of carbon-14 is 5730 years. [2]

• 1/4
• 1/8
• 1/16
• 1/32

10. Determine the half life of this isotope - just write the value/ number, answer in minutes