Chapter 7: Radioactivity & Nuclear Energy – Question Bank
Q1. Who discovered radioactivity and when?
Answer (short): Henri Becquerel, in 1896.
Q2. What is radioactivity?
Answer (descriptive): Radioactivity is the property of certain heavy elements to spontaneously disintegrate, emitting invisible rays and transforming into new elements. This process occurs due to instability in the nucleus caused by an imbalance in nuclear forces. Marie Curie coined the term "radioactivity" while studying Uranium and Thorium salts.
Q3. Name the three types of radiations emitted by radioactive elements.
Answer (short): Alpha (α), Beta (β), and Gamma (γ) rays.
Q4. Compare the properties of α, β, and γ rays.
| Property | α-rays | β-rays | γ-rays |
|---|---|---|---|
| Nature | Helium nuclei (2p + 2n) | High-speed electrons | Electromagnetic waves |
| Charge | +2 | –1 | 0 |
| Mass | 4 amu | 1/1837 amu | 0 |
| Penetrating Power | Least (stopped by paper) | Moderate (passes thin Al foil) | Highest (passes thick lead) |
| Ionising Power | Very high | Moderate | Very low |
| Effect on Nucleus | Z – 2, A – 4 | Z + 1 | No change in Z or A |
Q5. Explain the origin of α, β, and γ rays.
Answer (descriptive):
- α-rays: Emission of a helium nucleus reduces atomic number by 2 and mass number by 4.
- β-rays: A neutron transforms into a proton, releasing an electron from the nucleus; atomic number increases by 1.
- γ-rays: Emitted when the nucleus rearranges itself after α or β decay, releasing excess energy.
Q6. State three uses of radioactivity in different fields.
Answer (short):
- Medical – Co-60 for cancer, I-131 for thyroid disease, P-32 for leukemia.
- Archaeology – C-14 dating of fossils.
- Biology – Radioisotopes trace photosynthesis and protein synthesis.
Q7. What is nuclear energy?
Answer (descriptive): Nuclear energy is the energy stored within the atomic nucleus, released through nuclear fission or nuclear fusion. It arises due to the mass defect caused by nuclear binding forces, and is extremely high compared to chemical energy.
Q8. Define mass defect and binding energy.
Answer (short):
- Mass Defect (Δm): The difference between the sum of the masses of separate nucleons and the actual mass of the nucleus.
- Binding Energy: Energy required to separate all nucleons from a nucleus; calculated as E = Δm × 931 MeV.
Q9. Distinguish between nuclear fission and fusion.
| Aspect | Nuclear Fission | Nuclear Fusion |
|---|---|---|
| Process | Heavy nucleus splits into smaller nuclei | Light nuclei combine to form heavier nucleus |
| Example | U-235 + n → Ba + Kr + 3n + energy | ¹H + ¹H → ²He + energy |
| Energy Yield | Moderate | Very high |
| Requirements | Neutron bombardment | Extremely high temperature and pressure |
| Applications | Nuclear reactors, atom bombs | Hydrogen bombs, Sun’s energy |
Q10. Write two safety measures for nuclear power plants.
Answer (short):
- Build in earthquake-free and remote areas.
- Dispose radioactive waste safely.
Q11. What is the charge of an α-particle?
Answer: +2.
Q12. What is the speed of β-particles?
Answer: Nearly the speed of light.
Q13. Which radiation has the highest penetrating power?
Answer: Gamma rays.
Q14. Which radiation is stopped by a sheet of paper?
Answer: Alpha rays.
Q15. What does Z represent in nuclear notation?
Answer: Atomic number.
Q16. What does A represent in nuclear notation?
Answer: Mass number.
Q17. Name the scientist who coined the term "radioactivity".
Answer: Marie Curie.
Q18. Write the unit of binding energy.
Answer: MeV (Mega electron volt).
Q19. Which isotope is used for carbon dating?
Answer: Carbon-14.
Q20. Which isotope is used in the treatment of thyroid diseases?
Answer: Iodine-131.
Q21. Name one artificial radioactive element.
Answer: Plutonium-239.
Q22. Name the process responsible for the Sun’s energy.
Answer: Nuclear fusion.