Скачать или смотреть 27. 92U238 undergoes an alpha decay, followed by a beta-minus decay. What is the number of protons

92U238 undergoes an alpha decay, followed by a beta-minus decay. What is the number of protons and neutrons in the resulting nuclide?

This is a multiple-choice question from IBDP Paper 1, TZ0, May 2017, Physics SL exam. It's a classic example of a radioactive decay sequence, challenging your understanding of nuclear reactions and particle transformations. Alpha and beta decays are essential concepts in nuclear physics, and this question focuses on your ability to track changes in proton and neutron numbers through consecutive decays.
Concepts Involved
The question explores two main decay processes:
1. Alpha decay: In this process, the nucleus emits an alpha particle, which consists of 2 protons and 2 neutrons (essentially a helium nucleus). As a result, the atomic number decreases by 2, and the mass number decreases by 4.
2. Beta-minus decay: Here, a neutron converts into a proton and an electron. The proton stays in the nucleus, while the electron (beta particle) is emitted. The mass number remains unchanged, but the atomic number increases by 1 since a new proton is added.
The final task is to carefully follow these steps, update the proton and neutron counts, and identify the resulting nuclide.
Difficulty Level
This question requires a solid grasp of the basics of nuclear decay processes, specifically alpha and beta-minus decay. It tests both conceptual understanding and attention to detail, as missing any step can lead to an incorrect answer. Since the question involves multiple steps, students must carefully track the transformations to avoid errors.
While this is an intermediate-level question, some students might find it challenging to keep track of how both proton and neutron counts evolve across two decays. It is not mathematically intensive, but understanding and applying the logic behind particle conservation is crucial.
Solution Key (Without Full Steps)
• After the alpha decay, the atomic number decreases by 2, and the mass number decreases by 4.
• After the beta-minus decay, the atomic number increases by 1, while the mass number remains unchanged.
• The final proton and neutron count should reflect these adjustments.
The initial nuclide is uranium-238 with 92 protons and 146 neutrons (since 238 - 92 = 146). Use the changes mentioned above to determine the final proton and neutron counts.
Pause the video now and try solving it. If you don’t arrive at the correct answer, continue watching to understand the solution breakdown.
IBDP Learner Profiles and Skills Enriched
This question develops several key learner attributes. It encourages students to become thinkers, as they need to apply conceptual knowledge logically. It also promotes reflective learning, requiring students to reflect on their understanding of nuclear decay processes. Furthermore, this question enhances inquiry skills—students need to analyze data and draw conclusions based on scientific evidence.
The problem also nurtures skills such as problem-solving and critical thinking, as students must apply theoretical knowledge to solve practical problems. Attention to detail is crucial, as even a small mistake in tracking particle changes can lead to an incorrect answer.
Enrichment Concepts Related to the Problem
• Nuclear Stability: Understanding why certain elements undergo decay (like uranium-238) helps students appreciate nuclear stability and how isotopes strive to achieve a more stable configuration.
• Types of Radioactive Decay: This question highlights the two common decay modes (alpha and beta-minus) and how they contribute to nuclear transmutation.
• Real-world Applications: These decay processes are fundamental to understanding phenomena like nuclear energy, medical isotope production, and radiocarbon dating.
Enquiry Questions for Teachers
1. How does the emission of an alpha particle affect the stability of the resulting nucleus?
2. In what real-world applications are alpha and beta decays most commonly observed?
3. How do scientists use the concept of half-life to predict the behavior of decaying isotopes?
4. What is the difference between beta-minus and beta-plus decay, and when do they occur?
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