Half-life: how much is left

Answer Key - Grade 10 Science Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. 1.

   A radioactive sample goes through 3 half-lives. What percent of it is left, Ari?

   12.5 %
2. 2.

   A radioactive sample goes through 5 half-lives. What percent of it is left, Esme?

   3.125 %
4. 3.

   Using the bar, after how many half-lives is 12.5% left, Kira?

   • 3
   • 8
   • 12.5
5. 4.

   Using the bar, does halving ever bring the amount exactly to zero, Luz?

   Use the picture in question 3.

   • Yes: after 2 half-lives
   • No: it keeps getting smaller
   • Yes: after 4 half-lives
6. 5.

   What is a half-life, Milo?

   • Half the time for the whole sample
   • The sample's age
   • The time for half to decay
7. 6.

   What is carbon-14's half-life, Noah?

   • About 57 days
   • About 573 million years
   • About 5,730 years
8. 7.

   A 100 g radioactive sample passes one half-life. How much is left, Pia?

   • 25 g
   • 50 g
   • 0 g
9. 8.

   Technetium-99m, a medical tracer, has a half-life of 6.01 hours. Why is a short half-life useful, Ren?

   • It fades soon after the scan
   • It stays radioactive for centuries
   • It lasts for many years
10. 9.

    Which isotope is used to date ancient wood, Tala?

    • Technetium-99m
    • Fluorine-18
    • Carbon-14
11. 10.

    Why does carbon-14 work for things that were once alive, Zee?

    • Rocks are made of carbon-14
    • Living things take in carbon-14
    • Carbon-14 stays the same forever