Questions on Radioactive Decay
Radioactive Decay – Multiple-Choice Questions
1. What is radioactive decay?
A) The process of atoms absorbing neutrons
B) The breakdown of unstable atomic nuclei with emission of radiation
C) The fusion of two light elements into a heavier one
D) The loss of mass by physical evaporation
E) The loss of electrons in a chemical reaction
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2. Which of the following particles is released during alpha decay?
A) Two electrons
B) One neutron
C) One proton
D) Two protons and two neutrons
E) A high-energy photon
3. Beta-minus decay results in the emission of:
A) A neutron
B) A proton
C) A positron
D) An electron
E) A gamma ray
4. What is the result of alpha decay on the atomic number of the atom?
A) Increases by 2
B) Decreases by 2
C) Increases by 1
D) Decreases by 4
E) Stays the same
5. Which type of radiation is most easily blocked by paper?
A) Gamma rays
B) Beta particles
C) Alpha particles
D) Neutrons
E) X-rays
6. What is a common unit used to measure radioactive decay?
A) Hertz
B) Joule
C) Pascal
D) Becquerel
E) Ampere
7. The half-life of a radioactive isotope is:
A) Time for all atoms to decay
B) Time it takes to split an atom
C) Time for half the atoms in a sample to decay
D) Time to release all radiation
E) Time to absorb radiation
8. If a radioactive isotope has a half-life of 3 hours, how much of a 100 g sample remains after 6 hours?
A) 25 g
B) 50 g
C) 100 g
D) 75 g
E) 12.5 g
9. Which of the following statements is true about gamma radiation?
A) It has mass
B) It has charge
C) It can be deflected by magnetic fields
D) It is a form of electromagnetic radiation
E) It decreases atomic number
10. During beta-minus decay, what happens inside the nucleus?
A) A proton becomes a neutron
B) A neutron becomes a proton
C) Two protons are lost
D) A nucleus splits
E) Electrons are absorbed
11. What is the mass number of an alpha particle?
A) 0
B) 1
C) 2
D) 4
E) 8
12. What happens to the mass number during beta decay?
A) Increases by 1
B) Decreases by 1
C) Increases by 2
D) Stays the same
E) Decreases by 2
13. Which decay process emits a positron?
A) Alpha decay
B) Beta-minus decay
C) Gamma decay
D) Beta-plus decay
E) Neutron emission
14. Which of the following forms of radiation is not a particle?
A) Alpha
B) Beta
C) Gamma
D) Neutron
E) Positron
15. In which type of decay is a high-energy photon released?
A) Alpha
B) Beta-minus
C) Gamma
D) Positron
E) Neutron
16. A radioactive sample contains 80 g of material. After three half-lives, how much remains?
A) 10 g
B) 20 g
C) 40 g
D) 5 g
E) 15 g
17. The decay constant is related to:
A) The atomic number of the isotope
B) The energy released
C) The mass of the nucleus
D) The rate of radioactive decay
E) The number of neutrons
18. What is transmutation?
A) The splitting of an atom
B) Conversion of a solid to gas
C) A nuclear reaction changing one element to another
D) A phase change
E) A combustion reaction
19. Radioactive decay is considered what kind of process?
A) Physical
B) Chemical
C) Reversible
D) Random and spontaneous
E) Predictable to the second
20. Which of the following isotopes is useful in medical imaging due to its radioactive properties?
A) Oxygen-16
B) Carbon-12
C) Iodine-131
D) Hydrogen-1
E) Nitrogen-14
Answers with Explanations
1. B – Radioactive decay is the breakdown of unstable nuclei, emitting radiation.
2. D – Alpha particles consist of 2 protons and 2 neutrons (like helium nuclei).
3. D – Beta-minus decay releases an electron from the nucleus.
4. B – In alpha decay, the atomic number decreases by 2.
5. C – Alpha particles are easily blocked by paper due to low penetration power.
6. D – The becquerel (Bq) measures the number of disintegrations per second.
7. C – Half-life is the time it takes for half the atoms to decay.
8. A – After 6 hours (2 half-lives), 100 → 50 → 25 g remains.
9. D – Gamma rays are electromagnetic radiation with no mass or charge.
10. B – In beta-minus decay, a neutron becomes a proton.
11. D – An alpha particle has a mass number of 4 (2 protons + 2 neutrons).
12. D – Beta decay doesn't change the mass number (just the atomic number).
13. D – Beta-plus decay emits a positron (the antimatter of an electron).
14. C – Gamma rays are energy, not particles.
15. C – Gamma decay involves emission of high-energy photons.
16. B – 80 → 40 → 20 → 10 g remains after 3 half-lives.
17. D – The decay constant quantifies how quickly a substance decays.
18. C – Transmutation is when a radioactive decay transforms one element into another.
19. D – Decay is random for individual atoms but statistically predictable.
20. C – Iodine-131 is used in medical imaging, especially for the thyroid.
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