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Quiz Chapter 8: Radioactivity

10 questions ยท Form 3 Science Bab 8: Radioactivity

Question 1 of 10Score: 0

A radioactive sample decays from 120 g to 15 g in 24 hours. What is the half-life of this isotope?

Full Question List & Answer Key

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1. A radioactive sample decays from 120 g to 15 g in 24 hours. What is the half-life of this isotope?

  1. 4 hours
  2. 6 hours
  3. 8 hours
  4. 12 hours
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Answer: C

120 g -> 60 g -> 30 g -> 15 g requires 3 half-lives. 3 half-lives = 24 hours, so 1 half-life = 243 = 8 hours.

2. Which radioactive isotope is used by archeologists to estimate the age of ancient organic wood and bone fossils?

  1. Uranium-238
  2. Carbon-14
  3. Iodine-131
  4. Lead-206
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Answer: B

Carbon-14 radiocarbon dating measures remaining Carbon-14 activity in organic matter to determine fossil age up to ~50,000 years.

3. Why are radioactive substances safely stored inside thick lead containers?

  1. Lead neutralizes nuclear decay permanently.
  2. Lead absorbs penetrating ionising radiation like gamma rays.
  3. Lead increases the half-life of radioactive materials.
  4. Lead prevents chemical reactions with surrounding air.
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Answer: B

Lead has a high density and high atomic number, making it highly effective at absorbing alpha, beta, and penetrating gamma rays.

4. What safety tool should be used when handling unsealed radioactive laboratory sources to avoid direct contact?

  1. Rubber gloves only
  2. Robotic arms or long forceps/tongs
  3. Bare hands washed with soap
  4. Plastic tweezers
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Answer: B

Long tongs, forceps, or robotic arms maintain safe distance, reducing radiation exposure intensity according to the inverse-square law.

5. Which radioactive isotope is commonly used in medicine for cancer radiotherapy treatment?

  1. Carbon-14
  2. Cobalt-60
  3. Sodium-24
  4. Phosphorus-32
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Answer: B

Cobalt-60 emits high-energy gamma rays used in radiotherapy to destroy cancerous tumor cells.

6. A radioactive sample has an initial activity of 800 Bq. If its half-life is 10 days, what will its activity be after 30 days?

  1. 400 Bq
  2. 200 Bq
  3. 100 Bq
  4. 50 Bq
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Answer: C

Number of half-lives = 3010 = 3 half-lives. Activity drops: 800 -> 400 -> 200 -> 100 Bq.

7. Which of the following is classified as NON-IONISING radiation?

  1. Gamma rays
  2. Alpha particles
  3. Microwaves
  4. X-rays
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Answer: C

Microwaves belong to non-ionising radiation on the electromagnetic spectrum, lacking sufficient energy to ionize atoms.

8. How does a neutral atom transform into a positive ion (cation)?

  1. By gaining one or more protons
  2. By losing one or more electrons
  3. By gaining one or more electrons
  4. By losing neutrons from its nucleus
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Answer: B

A positive ion is formed when an atom loses negative electrons, resulting in more positive protons than negative electrons.

9. What happens to a beam of Beta (\beta) particles when passed through an electric field?

  1. Deflected towards the positive electric plate
  2. Deflected towards the negative electric plate
  3. Passes straight through without deflection
  4. Reflected back to the source
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Answer: A

Beta particles are high-speed negatively charged electrons ($^0_{-1}e$), so they are attracted toward the positive electric plate.

10. What is the S.I. unit for measuring radioactivity decay rate?

  1. Sievert (Sv)
  2. Curie (Ci)
  3. Becquerel (Bq)
  4. Gray (Gy)
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Answer: C

The S.I. unit of radioactivity is the Becquerel (Bq), defined as one decay per second.

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