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 608 g and a half-life of 6 days. How many grams of the isotope remain undecayed after 30 days?
N₀ = 608 g (t₁/₂ = 6 d) · t = 30 days
2. A radioactive sample has an initial mass of 48 g and a half-life of 8 days. How many grams of the isotope remain undecayed after 16 days?
N₀ = 48 g (t₁/₂ = 8 d) · t = 16 days
3. A radioactive sample has an initial mass of 320 g and a half-life of 10 days. How many grams of the isotope remain undecayed after 40 days?
N₀ = 320 g (t₁/₂ = 10 d) · t = 40 days
4. A radioactive sample has an initial mass of 184 g and a half-life of 9 days. How many grams of the isotope remain undecayed after 27 days?
N₀ = 184 g (t₁/₂ = 9 d) · t = 27 days
5. A radioactive sample has an initial mass of 64 g and a half-life of 7 days. How many grams of the isotope remain undecayed after 14 days?
N₀ = 64 g (t₁/₂ = 7 d) · t = 14 days
6. A radioactive sample has an initial mass of 18 g and a half-life of 2 days. How many grams of the isotope remain undecayed after 2 days?
N₀ = 18 g (t₁/₂ = 2 d) · t = 2 days
7. A radioactive sample has an initial mass of 544 g and a half-life of 8 days. How many grams of the isotope remain undecayed after 40 days?
N₀ = 544 g (t₁/₂ = 8 d) · t = 40 days
8. A radioactive sample has an initial mass of 112 g and a half-life of 5 days. How many grams of the isotope remain undecayed after 15 days?
N₀ = 112 g (t₁/₂ = 5 d) · t = 15 days
9. A radioactive sample has an initial mass of 28 g and a half-life of 10 days. How many grams of the isotope remain undecayed after 10 days?
N₀ = 28 g (t₁/₂ = 10 d) · t = 10 days
10. A radioactive sample has an initial mass of 512 g and a half-life of 12 days. How many grams of the isotope remain undecayed after 60 days?
N₀ = 512 g (t₁/₂ = 12 d) · t = 60 days
11. A radioactive sample has an initial mass of 80 g and a half-life of 8 days. How many grams of the isotope remain undecayed after 24 days?
N₀ = 80 g (t₁/₂ = 8 d) · t = 24 days
12. A radioactive sample has an initial mass of 576 g and a half-life of 7 days. How many grams of the isotope remain undecayed after 35 days?
N₀ = 576 g (t₁/₂ = 7 d) · t = 35 days

12 questions · Seed 43 · 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 608 g and a half-life of 6 days. How many grams of the isotope remain undecayed after 30 days?
19 g
Number of half-lives = 30 ÷ 6 = 5. Remaining mass = 608 ÷ 2^5 = 19 g.
2. A radioactive sample has an initial mass of 48 g and a half-life of 8 days. How many grams of the isotope remain undecayed after 16 days?
12 g
Number of half-lives = 16 ÷ 8 = 2. Remaining mass = 48 ÷ 2^2 = 12 g.
3. A radioactive sample has an initial mass of 320 g and a half-life of 10 days. How many grams of the isotope remain undecayed after 40 days?
20 g
Number of half-lives = 40 ÷ 10 = 4. Remaining mass = 320 ÷ 2^4 = 20 g.
4. A radioactive sample has an initial mass of 184 g and a half-life of 9 days. How many grams of the isotope remain undecayed after 27 days?
23 g
Number of half-lives = 27 ÷ 9 = 3. Remaining mass = 184 ÷ 2^3 = 23 g.
5. A radioactive sample has an initial mass of 64 g and a half-life of 7 days. How many grams of the isotope remain undecayed after 14 days?
16 g
Number of half-lives = 14 ÷ 7 = 2. Remaining mass = 64 ÷ 2^2 = 16 g.
6. A radioactive sample has an initial mass of 18 g and a half-life of 2 days. How many grams of the isotope remain undecayed after 2 days?
9 g
Number of half-lives = 2 ÷ 2 = 1. Remaining mass = 18 ÷ 2^1 = 9 g.
7. A radioactive sample has an initial mass of 544 g and a half-life of 8 days. How many grams of the isotope remain undecayed after 40 days?
17 g
Number of half-lives = 40 ÷ 8 = 5. Remaining mass = 544 ÷ 2^5 = 17 g.
8. A radioactive sample has an initial mass of 112 g and a half-life of 5 days. How many grams of the isotope remain undecayed after 15 days?
14 g
Number of half-lives = 15 ÷ 5 = 3. Remaining mass = 112 ÷ 2^3 = 14 g.
9. A radioactive sample has an initial mass of 28 g and a half-life of 10 days. How many grams of the isotope remain undecayed after 10 days?
14 g
Number of half-lives = 10 ÷ 10 = 1. Remaining mass = 28 ÷ 2^1 = 14 g.
10. A radioactive sample has an initial mass of 512 g and a half-life of 12 days. How many grams of the isotope remain undecayed after 60 days?
16 g
Number of half-lives = 60 ÷ 12 = 5. Remaining mass = 512 ÷ 2^5 = 16 g.
11. A radioactive sample has an initial mass of 80 g and a half-life of 8 days. How many grams of the isotope remain undecayed after 24 days?
10 g
Number of half-lives = 24 ÷ 8 = 3. Remaining mass = 80 ÷ 2^3 = 10 g.
12. A radioactive sample has an initial mass of 576 g and a half-life of 7 days. How many grams of the isotope remain undecayed after 35 days?
18 g
Number of half-lives = 35 ÷ 7 = 5. Remaining mass = 576 ÷ 2^5 = 18 g.

12 questions · Seed 43 · 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 608 g and a half-life of 6 days. How many grams of the isotope remain undecayed after 30 days?
N₀ = 608 g (t₁/₂ = 6 d) · t = 30 days
2. A radioactive sample has an initial mass of 48 g and a half-life of 8 days. How many grams of the isotope remain undecayed after 16 days?
N₀ = 48 g (t₁/₂ = 8 d) · t = 16 days
3. A radioactive sample has an initial mass of 320 g and a half-life of 10 days. How many grams of the isotope remain undecayed after 40 days?
N₀ = 320 g (t₁/₂ = 10 d) · t = 40 days
4. A radioactive sample has an initial mass of 184 g and a half-life of 9 days. How many grams of the isotope remain undecayed after 27 days?
N₀ = 184 g (t₁/₂ = 9 d) · t = 27 days
5. A radioactive sample has an initial mass of 64 g and a half-life of 7 days. How many grams of the isotope remain undecayed after 14 days?
N₀ = 64 g (t₁/₂ = 7 d) · t = 14 days
6. A radioactive sample has an initial mass of 18 g and a half-life of 2 days. How many grams of the isotope remain undecayed after 2 days?
N₀ = 18 g (t₁/₂ = 2 d) · t = 2 days
7. A radioactive sample has an initial mass of 544 g and a half-life of 8 days. How many grams of the isotope remain undecayed after 40 days?
N₀ = 544 g (t₁/₂ = 8 d) · t = 40 days
8. A radioactive sample has an initial mass of 112 g and a half-life of 5 days. How many grams of the isotope remain undecayed after 15 days?
N₀ = 112 g (t₁/₂ = 5 d) · t = 15 days
9. A radioactive sample has an initial mass of 28 g and a half-life of 10 days. How many grams of the isotope remain undecayed after 10 days?
N₀ = 28 g (t₁/₂ = 10 d) · t = 10 days
10. A radioactive sample has an initial mass of 512 g and a half-life of 12 days. How many grams of the isotope remain undecayed after 60 days?
N₀ = 512 g (t₁/₂ = 12 d) · t = 60 days
11. A radioactive sample has an initial mass of 80 g and a half-life of 8 days. How many grams of the isotope remain undecayed after 24 days?
N₀ = 80 g (t₁/₂ = 8 d) · t = 24 days
12. A radioactive sample has an initial mass of 576 g and a half-life of 7 days. How many grams of the isotope remain undecayed after 35 days?
N₀ = 576 g (t₁/₂ = 7 d) · t = 35 days

12 questions · Seed 43 · 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 608 g and a half-life of 6 days. How many grams of the isotope remain undecayed after 30 days?
19 g
Number of half-lives = 30 ÷ 6 = 5. Remaining mass = 608 ÷ 2^5 = 19 g.
2. A radioactive sample has an initial mass of 48 g and a half-life of 8 days. How many grams of the isotope remain undecayed after 16 days?
12 g
Number of half-lives = 16 ÷ 8 = 2. Remaining mass = 48 ÷ 2^2 = 12 g.
3. A radioactive sample has an initial mass of 320 g and a half-life of 10 days. How many grams of the isotope remain undecayed after 40 days?
20 g
Number of half-lives = 40 ÷ 10 = 4. Remaining mass = 320 ÷ 2^4 = 20 g.
4. A radioactive sample has an initial mass of 184 g and a half-life of 9 days. How many grams of the isotope remain undecayed after 27 days?
23 g
Number of half-lives = 27 ÷ 9 = 3. Remaining mass = 184 ÷ 2^3 = 23 g.
5. A radioactive sample has an initial mass of 64 g and a half-life of 7 days. How many grams of the isotope remain undecayed after 14 days?
16 g
Number of half-lives = 14 ÷ 7 = 2. Remaining mass = 64 ÷ 2^2 = 16 g.
6. A radioactive sample has an initial mass of 18 g and a half-life of 2 days. How many grams of the isotope remain undecayed after 2 days?
9 g
Number of half-lives = 2 ÷ 2 = 1. Remaining mass = 18 ÷ 2^1 = 9 g.
7. A radioactive sample has an initial mass of 544 g and a half-life of 8 days. How many grams of the isotope remain undecayed after 40 days?
17 g
Number of half-lives = 40 ÷ 8 = 5. Remaining mass = 544 ÷ 2^5 = 17 g.
8. A radioactive sample has an initial mass of 112 g and a half-life of 5 days. How many grams of the isotope remain undecayed after 15 days?
14 g
Number of half-lives = 15 ÷ 5 = 3. Remaining mass = 112 ÷ 2^3 = 14 g.
9. A radioactive sample has an initial mass of 28 g and a half-life of 10 days. How many grams of the isotope remain undecayed after 10 days?
14 g
Number of half-lives = 10 ÷ 10 = 1. Remaining mass = 28 ÷ 2^1 = 14 g.
10. A radioactive sample has an initial mass of 512 g and a half-life of 12 days. How many grams of the isotope remain undecayed after 60 days?
16 g
Number of half-lives = 60 ÷ 12 = 5. Remaining mass = 512 ÷ 2^5 = 16 g.
11. A radioactive sample has an initial mass of 80 g and a half-life of 8 days. How many grams of the isotope remain undecayed after 24 days?
10 g
Number of half-lives = 24 ÷ 8 = 3. Remaining mass = 80 ÷ 2^3 = 10 g.
12. A radioactive sample has an initial mass of 576 g and a half-life of 7 days. How many grams of the isotope remain undecayed after 35 days?
18 g
Number of half-lives = 35 ÷ 7 = 5. Remaining mass = 576 ÷ 2^5 = 18 g.

12 questions · Seed 43 · Age guidance, not curriculum certification