Year 9 Physics: Different Half-Lives of Radioactive Isotopes

Introduction to Radioactive Isotopes

Hello Year 9! Today, we will explore a fascinating topic in physics: radioactive isotopes and their half-lives. This is a key concept that helps us understand how certain elements decay over time.

What is a Radioactive Isotope?

A radioactive isotope, or radioisotope, is a version of an element that has an unstable nucleus. This means that it can break down and release energy in the form of radiation. Over time, these isotopes decay into different elements or isotopes.

What is a Half-Life?

The half-life of a radioactive isotope is the time it takes for half of the radioactive atoms in a sample to decay. This is a crucial concept because it tells us how quickly or slowly a radioactive isotope will lose its radioactivity.

Example of Half-Life

Let’s consider an example using Carbon-14, a radioactive isotope of carbon. The half-life of Carbon-14 is about 5,730 years. This means that if you start with 1000 grams of Carbon-14, after 5,730 years, you will have 500 grams left. After another 5,730 years (which totals 11,460 years), you will have 250 grams remaining, and so on.

Key Rules About Half-Lives

1. Constant Rate: The half-life of a specific isotope is constant. This means it will always take the same amount of time for half of the sample to decay, no matter how much of it you start with.
2. Exponential Decay: The amount of the radioactive substance decreases exponentially. This means that it will take longer to decay the further you go (after several half-lives, you’ll have very little left).
3. Different Isotopes, Different Half-Lives: Different isotopes have different half-lives. For example, Uranium-238 has a half-life of about 4.5 billion years, while Polonium-210 has a half-life of only 138 days.

Tips and Tricks to Remember

• Visualisation: Draw a graph showing the decay of a radioactive isotope over time. The curve will show a steep drop-off at first, which gradually flattens.
• Practice Problems: Work on problems involving calculations of remaining amounts after several half-lives.
• Use Mnemonics: Create a short phrase or rhyme to remember key half-lives of common isotopes.

Questions

Easy Level Questions (1-20)

1. What is a radioactive isotope?
2. What does half-life mean?
3. How long is the half-life of Carbon-14?
4. If you have 100 grams of a radioactive substance after one half-life, how much will you have left after two half-lives?
5. True or False: The half-life of an isotope changes based on the amount you start with.
6. What happens to a radioactive isotope over time?
7. Name one example of a radioactive isotope.
8. How is half-life measured?
9. If the half-life of an isotope is 10 years, how much will remain after 20 years?
10. True or False: Half-lives are always the same for all isotopes.
11. If you start with 80 grams of a substance, how much is left after one half-life?
12. What kind of radiation do radioactive isotopes emit?
13. Name a use of radioactive isotopes in medicine.
14. How many half-lives does it take to reduce a sample to 25% of its original amount?
15. What is the half-life of Uranium-238?
16. How does the concept of half-life help scientists?
17. Is a longer half-life associated with a more stable or unstable isotope?
18. What is the half-life of Polonium-210?
19. If you have 200 grams of an isotope with a half-life of 4 years, how much is left after 8 years?
20. What does it mean if an isotope has a very short half-life?

Medium Level Questions (21-40)

21. Calculate the remaining mass of a 160 g sample of an isotope after 3 half-lives if its half-life is 5 years.
22. Explain the difference between a stable and an unstable isotope.
23. What is the significance of understanding half-lives in archaeology?
24. How can half-lives be used in carbon dating?
25. If an isotope has a half-life of 2 years, how much of a 32 g sample will remain after 8 years?
26. Why do different isotopes have different half-lives?
27. Describe the process that occurs during radioactive decay.
28. If you started with 64 grams of an isotope, how much will be left after 4 half-lives?
29. How does temperature affect the half-life of a radioactive isotope?
30. What role does half-life play in nuclear power generation?
31. How can scientists determine the age of ancient artifacts using half-lives?
32. What is meant by ‘exponential decay’ in the context of half-lives?
33. If an isotope decays to a stable form, what does that mean?
34. How can the concept of half-life be applied in environmental studies?
35. Why is it important to know the half-life of a radioactive isotope in medicine?
36. If a substance has a half-life of 3 days, how much would remain after 12 days?
37. Discuss one real-world application of radioactive isotopes.
38. What happens to the radiation emitted during decay?
39. If after 10 years, 75 grams of a radioactive substance remains, what is the half-life?
40. How do scientists measure the half-lives of isotopes?

Hard Level Questions (41-60)

41. Describe how radioactive decay can be used to date geological formations.
42. If an isotope has a half-life of 10 days, how much of a 256 g sample will remain after 40 days?
43. Discuss the implications of long vs. short half-lives in waste management.
44. Explain how half-lives can affect the safety of nuclear waste.
45. If a substance has three half-lives, how much of the original sample remains as a percentage?
46. How can the concept of half-life be used to understand nuclear fission?
47. Compare and contrast the half-lives of Carbon-14 and Uranium-238.
48. How does the half-life of an isotope influence its use in medical diagnostics?
49. If you start with 500 g of an isotope with a half-life of 6 years, how much will be left after 18 years?
50. Discuss how scientists use half-lives to predict the behaviour of radioactive materials over time.
51. If a sample of a radioactive isotope has a half-life of 5 years and is currently 12.5 g, what was its original mass?
52. Explain how radioactive isotopes can be used to track environmental changes.
53. Compare the decay rates of two isotopes with different half-lives.
54. If the half-life of a substance is 15 years, how long will it take for it to decay to less than 10% of its original mass?
55. Discuss the concept of a decay chain and its relation to half-lives.
56. How do physicists determine the half-lives of newly discovered isotopes?
57. If the half-life of a radioactive element is 50 years, what fraction of the original sample remains after 200 years?
58. Describe the safety measures in place when handling radioactive materials in a lab.
59. Explain the significance of the longest half-lives in terms of geological time.
60. How can the concept of half-lives aid in understanding the stability of different elements in the periodic table?

Answers and Explanations

Easy Level Answers

1. A version of an element with an unstable nucleus.
2. The time it takes for half of a radioactive sample to decay.
3. About 5,730 years.
4. 25 grams.
5. True.
6. It decays into different elements or isotopes.
7. Carbon-14.
8. In time (years).
9. 0 grams (it will be completely decayed).
10. False.
11. 40 grams.
12. Alpha, beta, and gamma radiation.
13. Radiation therapy for cancer.
14. Two half-lives.
15. About 4.5 billion years.
16. It helps estimate ages of materials and understand decay rates.
17. More stable.
18. 138 days.
19. 50 grams.
20. It decays very quickly.

Medium Level Answers

21. 20 g.
22. Stable isotopes do not decay; unstable isotopes do.
23. It helps determine the age of fossils and ancient remains (carbon dating).
24. Carbon dating uses the half-life of Carbon-14 to date organic materials.
25. 2 g.
26. It depends on the stability of the nucleus.
27. The nucleus emits radiation and transforms into a different element.
28. 4 grams.
29. It typically does not affect the half-life significantly.
30. It can help in controlling reactions and managing fuel.
31. By measuring the remaining Carbon-14.
32. The amount decreases rapidly at first, then slows down.
33. The isotope becomes a stable form, often a non-radioactive element.
34. To assess pollution levels and the decay of contaminants.
35. To understand how long a substance will remain active in the body.
36. 15 g.
37. Medical imaging, cancer treatment, and archaeological dating.
38. It can be absorbed or cause changes in other materials.
39. 2.5 years.
40. Through experiments, radiation measurements, and decay patterns.

Hard Level Answers

41. By measuring the isotopes present in rock layers.
42. 16 g.
43. Long half-lives are harder to manage; short half-lives decay quicker.
44. Longer half-lives pose risks if not properly managed.
45. 12.5%.
46. It helps to understand the energy release in reactions.
47. Carbon-14 is short (5,730 years); Uranium-238 is long (4.5 billion years).
48. It determines how long a tracer will be effective.
49. 62.5 g.
50. They can estimate how long materials will remain hazardous.
51. 1000 g.
52. By tracking isotopes released during events (like pollution).
53. The one with a longer half-life decays slower.
54. 60 years.
55. A sequence of decay where one isotope decays into another.
56. By studying decay rates and radiation emissions.
57. 1/16 of the original sample remains.
58. Use protective gear and follow safety protocols.
59. They help understand the Earth’s history.
60. It shows which elements are more stable over time.

Feel free to ask any questions if you need more clarification on any of the topics!