ScienceAges 16-18

Radioactive half-life decay

Calculate the remaining activity (Bq) of a radioactive sample after a whole number of half-lives. Review suitability for your learners before teaching.

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Worksheet StudioPractice pack · Ages 16-18

Radioactive half-life decay

Take your time. Show your thinking.

1. A radioactive sample has an initial mass of 224 g and a half-life of 8 days. How many grams of the isotope remain undecayed after 32 days?
N₀ = 224 g (t₁/₂ = 8 d) · t = 32 days
2. A radioactive sample has an initial mass of 18 g and a half-life of 3 days. How many grams of the isotope remain undecayed after 3 days?
N₀ = 18 g (t₁/₂ = 3 d) · t = 3 days
3. A radioactive sample has an initial mass of 576 g and a half-life of 2 days. How many grams of the isotope remain undecayed after 10 days?
N₀ = 576 g (t₁/₂ = 2 d) · t = 10 days
4. A radioactive sample has an initial mass of 480 g and a half-life of 12 days. How many grams of the isotope remain undecayed after 60 days?
N₀ = 480 g (t₁/₂ = 12 d) · t = 60 days
5. A radioactive sample has an initial mass of 200 g and a half-life of 2 days. How many grams of the isotope remain undecayed after 6 days?
N₀ = 200 g (t₁/₂ = 2 d) · t = 6 days
6. A radioactive sample has an initial mass of 128 g and a half-life of 5 days. How many grams of the isotope remain undecayed after 20 days?
N₀ = 128 g (t₁/₂ = 5 d) · t = 20 days
7. A radioactive sample has an initial mass of 18 g and a half-life of 10 days. How many grams of the isotope remain undecayed after 10 days?
N₀ = 18 g (t₁/₂ = 10 d) · t = 10 days
8. A radioactive sample has an initial mass of 304 g and a half-life of 11 days. How many grams of the isotope remain undecayed after 44 days?
N₀ = 304 g (t₁/₂ = 11 d) · t = 44 days
9. A radioactive sample has an initial mass of 40 g and a half-life of 3 days. How many grams of the isotope remain undecayed after 3 days?
N₀ = 40 g (t₁/₂ = 3 d) · t = 3 days
10. A radioactive sample has an initial mass of 128 g and a half-life of 12 days. How many grams of the isotope remain undecayed after 48 days?
N₀ = 128 g (t₁/₂ = 12 d) · t = 48 days
11. A radioactive sample has an initial mass of 44 g and a half-life of 9 days. How many grams of the isotope remain undecayed after 18 days?
N₀ = 44 g (t₁/₂ = 9 d) · t = 18 days
12. A radioactive sample has an initial mass of 736 g and a half-life of 11 days. How many grams of the isotope remain undecayed after 55 days?
N₀ = 736 g (t₁/₂ = 11 d) · t = 55 days

12 questions · Seed 47 · Age guidance, not curriculum certification

View the answer key

Worksheet StudioAnswer key · Ages 16-18

Radioactive half-life decay

Answers and reasoning. Review before teaching.

1. A radioactive sample has an initial mass of 224 g and a half-life of 8 days. How many grams of the isotope remain undecayed after 32 days?
14 g
Number of half-lives = 32 ÷ 8 = 4. Remaining mass = 224 ÷ 2^4 = 14 g.
2. A radioactive sample has an initial mass of 18 g and a half-life of 3 days. How many grams of the isotope remain undecayed after 3 days?
9 g
Number of half-lives = 3 ÷ 3 = 1. Remaining mass = 18 ÷ 2^1 = 9 g.
3. A radioactive sample has an initial mass of 576 g and a half-life of 2 days. How many grams of the isotope remain undecayed after 10 days?
18 g
Number of half-lives = 10 ÷ 2 = 5. Remaining mass = 576 ÷ 2^5 = 18 g.
4. A radioactive sample has an initial mass of 480 g and a half-life of 12 days. How many grams of the isotope remain undecayed after 60 days?
15 g
Number of half-lives = 60 ÷ 12 = 5. Remaining mass = 480 ÷ 2^5 = 15 g.
5. A radioactive sample has an initial mass of 200 g and a half-life of 2 days. How many grams of the isotope remain undecayed after 6 days?
25 g
Number of half-lives = 6 ÷ 2 = 3. Remaining mass = 200 ÷ 2^3 = 25 g.
6. A radioactive sample has an initial mass of 128 g and a half-life of 5 days. How many grams of the isotope remain undecayed after 20 days?
8 g
Number of half-lives = 20 ÷ 5 = 4. Remaining mass = 128 ÷ 2^4 = 8 g.
7. A radioactive sample has an initial mass of 18 g and a half-life of 10 days. How many grams of the isotope remain undecayed after 10 days?
9 g
Number of half-lives = 10 ÷ 10 = 1. Remaining mass = 18 ÷ 2^1 = 9 g.
8. A radioactive sample has an initial mass of 304 g and a half-life of 11 days. How many grams of the isotope remain undecayed after 44 days?
19 g
Number of half-lives = 44 ÷ 11 = 4. Remaining mass = 304 ÷ 2^4 = 19 g.
9. A radioactive sample has an initial mass of 40 g and a half-life of 3 days. How many grams of the isotope remain undecayed after 3 days?
20 g
Number of half-lives = 3 ÷ 3 = 1. Remaining mass = 40 ÷ 2^1 = 20 g.
10. A radioactive sample has an initial mass of 128 g and a half-life of 12 days. How many grams of the isotope remain undecayed after 48 days?
8 g
Number of half-lives = 48 ÷ 12 = 4. Remaining mass = 128 ÷ 2^4 = 8 g.
11. A radioactive sample has an initial mass of 44 g and a half-life of 9 days. How many grams of the isotope remain undecayed after 18 days?
11 g
Number of half-lives = 18 ÷ 9 = 2. Remaining mass = 44 ÷ 2^2 = 11 g.
12. A radioactive sample has an initial mass of 736 g and a half-life of 11 days. How many grams of the isotope remain undecayed after 55 days?
23 g
Number of half-lives = 55 ÷ 11 = 5. Remaining mass = 736 ÷ 2^5 = 23 g.

12 questions · Seed 47 · Age guidance, not curriculum certification

Worksheet StudioPractice pack · Ages 16-18

Radioactive half-life decay

Take your time. Show your thinking.

1. A radioactive sample has an initial mass of 224 g and a half-life of 8 days. How many grams of the isotope remain undecayed after 32 days?
N₀ = 224 g (t₁/₂ = 8 d) · t = 32 days
2. A radioactive sample has an initial mass of 18 g and a half-life of 3 days. How many grams of the isotope remain undecayed after 3 days?
N₀ = 18 g (t₁/₂ = 3 d) · t = 3 days
3. A radioactive sample has an initial mass of 576 g and a half-life of 2 days. How many grams of the isotope remain undecayed after 10 days?
N₀ = 576 g (t₁/₂ = 2 d) · t = 10 days
4. A radioactive sample has an initial mass of 480 g and a half-life of 12 days. How many grams of the isotope remain undecayed after 60 days?
N₀ = 480 g (t₁/₂ = 12 d) · t = 60 days
5. A radioactive sample has an initial mass of 200 g and a half-life of 2 days. How many grams of the isotope remain undecayed after 6 days?
N₀ = 200 g (t₁/₂ = 2 d) · t = 6 days
6. A radioactive sample has an initial mass of 128 g and a half-life of 5 days. How many grams of the isotope remain undecayed after 20 days?
N₀ = 128 g (t₁/₂ = 5 d) · t = 20 days
7. A radioactive sample has an initial mass of 18 g and a half-life of 10 days. How many grams of the isotope remain undecayed after 10 days?
N₀ = 18 g (t₁/₂ = 10 d) · t = 10 days
8. A radioactive sample has an initial mass of 304 g and a half-life of 11 days. How many grams of the isotope remain undecayed after 44 days?
N₀ = 304 g (t₁/₂ = 11 d) · t = 44 days
9. A radioactive sample has an initial mass of 40 g and a half-life of 3 days. How many grams of the isotope remain undecayed after 3 days?
N₀ = 40 g (t₁/₂ = 3 d) · t = 3 days
10. A radioactive sample has an initial mass of 128 g and a half-life of 12 days. How many grams of the isotope remain undecayed after 48 days?
N₀ = 128 g (t₁/₂ = 12 d) · t = 48 days
11. A radioactive sample has an initial mass of 44 g and a half-life of 9 days. How many grams of the isotope remain undecayed after 18 days?
N₀ = 44 g (t₁/₂ = 9 d) · t = 18 days
12. A radioactive sample has an initial mass of 736 g and a half-life of 11 days. How many grams of the isotope remain undecayed after 55 days?
N₀ = 736 g (t₁/₂ = 11 d) · t = 55 days

12 questions · Seed 47 · Age guidance, not curriculum certification

Worksheet StudioAnswer key · Ages 16-18

Radioactive half-life decay

Answers and reasoning. Review before teaching.

1. A radioactive sample has an initial mass of 224 g and a half-life of 8 days. How many grams of the isotope remain undecayed after 32 days?
14 g
Number of half-lives = 32 ÷ 8 = 4. Remaining mass = 224 ÷ 2^4 = 14 g.
2. A radioactive sample has an initial mass of 18 g and a half-life of 3 days. How many grams of the isotope remain undecayed after 3 days?
9 g
Number of half-lives = 3 ÷ 3 = 1. Remaining mass = 18 ÷ 2^1 = 9 g.
3. A radioactive sample has an initial mass of 576 g and a half-life of 2 days. How many grams of the isotope remain undecayed after 10 days?
18 g
Number of half-lives = 10 ÷ 2 = 5. Remaining mass = 576 ÷ 2^5 = 18 g.
4. A radioactive sample has an initial mass of 480 g and a half-life of 12 days. How many grams of the isotope remain undecayed after 60 days?
15 g
Number of half-lives = 60 ÷ 12 = 5. Remaining mass = 480 ÷ 2^5 = 15 g.
5. A radioactive sample has an initial mass of 200 g and a half-life of 2 days. How many grams of the isotope remain undecayed after 6 days?
25 g
Number of half-lives = 6 ÷ 2 = 3. Remaining mass = 200 ÷ 2^3 = 25 g.
6. A radioactive sample has an initial mass of 128 g and a half-life of 5 days. How many grams of the isotope remain undecayed after 20 days?
8 g
Number of half-lives = 20 ÷ 5 = 4. Remaining mass = 128 ÷ 2^4 = 8 g.
7. A radioactive sample has an initial mass of 18 g and a half-life of 10 days. How many grams of the isotope remain undecayed after 10 days?
9 g
Number of half-lives = 10 ÷ 10 = 1. Remaining mass = 18 ÷ 2^1 = 9 g.
8. A radioactive sample has an initial mass of 304 g and a half-life of 11 days. How many grams of the isotope remain undecayed after 44 days?
19 g
Number of half-lives = 44 ÷ 11 = 4. Remaining mass = 304 ÷ 2^4 = 19 g.
9. A radioactive sample has an initial mass of 40 g and a half-life of 3 days. How many grams of the isotope remain undecayed after 3 days?
20 g
Number of half-lives = 3 ÷ 3 = 1. Remaining mass = 40 ÷ 2^1 = 20 g.
10. A radioactive sample has an initial mass of 128 g and a half-life of 12 days. How many grams of the isotope remain undecayed after 48 days?
8 g
Number of half-lives = 48 ÷ 12 = 4. Remaining mass = 128 ÷ 2^4 = 8 g.
11. A radioactive sample has an initial mass of 44 g and a half-life of 9 days. How many grams of the isotope remain undecayed after 18 days?
11 g
Number of half-lives = 18 ÷ 9 = 2. Remaining mass = 44 ÷ 2^2 = 11 g.
12. A radioactive sample has an initial mass of 736 g and a half-life of 11 days. How many grams of the isotope remain undecayed after 55 days?
23 g
Number of half-lives = 55 ÷ 11 = 5. Remaining mass = 736 ÷ 2^5 = 23 g.

12 questions · Seed 47 · Age guidance, not curriculum certification