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UPSC Prelims Quiz: March 13, 2026

Q1. Which of the following best explains the primary role of the high-energy proton accelerator proposed in Visakhapatnam?
(a) To generate electricity directly through proton-induced nuclear fission
(b) To produce neutrons through spallation for sustaining reactions in sub-critical nuclear reactors
(c) To convert thorium directly into plutonium-239
(d) To generate controlled thermonuclear fusion reactions
Explanation
The high-energy proton accelerator does not generate electricity directly.
  • accelerate protons using electromagnetic fields
  • strike a heavy metal target (lead/bismuth)
  • trigger spallation reactions
  • produce large numbers of neutrons
These neutrons are then supplied to a sub-critical reactor core in an Accelerator-Driven System to sustain nuclear fission.
Correct Answer: (b)
Why others are wrong
  • (a) Proton beams do not directly generate electricity.
  • (c) Thorium converts into Uranium-233, not plutonium-239.
  • (d) ADS technology is related to fission reactors, not fusion.
Q2. With reference to India’s thorium-based nuclear energy strategy, consider the following statements:
1. Thorium-232 is classified as a fertile material because it cannot undergo fission directly with thermal neutrons.
2. Accelerator-Driven Systems can facilitate the conversion of thorium into Uranium-233 through neutron capture processes.
3. Uranium-233 produced from thorium is a fissile isotope capable of sustaining nuclear fission.
(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
Explanation
Statement 1 – Correct
Thorium-232 is fertile, not fissile.
It cannot sustain a nuclear chain reaction on its own and must first absorb a neutron.
Statement 2 – Correct
In ADS systems, the high neutron flux generated by spallation can bombard thorium and convert it through nuclear transmutation.
Statement 3 – Correct
After neutron capture and beta decay, Thorium-232 ultimately converts into Uranium-233, which is a fissile isotope capable of sustaining nuclear fission.
U-233 is therefore a key fuel in India’s long-term thorium fuel cycle.
Correct Answer: (d) 1, 2 and 3
Q3. With reference to Accelerator-Driven Systems (ADS), consider the following statements:
1. ADS reactors operate in a sub-critical state and therefore cannot maintain a self-sustaining chain reaction without an external neutron source.
2. The neutron source in ADS is produced through spallation when high-energy protons strike a heavy metal target.
3. The neutron flux generated in ADS can enable both thorium breeding and transmutation of long-lived radioactive waste.
(a) 1 only
(b) 1 and 2 only
(c) 1 and 3 only
(d) 1, 2 and 3
Explanation
Statement 1 – Correct
ADS reactors are designed with a sub-critical core, meaning the neutron multiplication factor remains below one.
Hence, they cannot sustain a chain reaction independently and depend on an external neutron source.
Statement 2 – Correct
The external neutron source comes from spallation reactions, produced when a high-energy proton beam from a particle accelerator strikes a heavy metal target such as lead or bismuth.
Statement 3 – Correct
The intense neutron flux generated can serve two major purposes:
  • Breeding fissile fuel by converting Thorium-232 into Uranium-233
  • Transmuting long-lived nuclear waste (e.g., minor actinides) into shorter-lived isotopes
Both are key motivations behind ADS research globally.
Correct Answer: (d) 1, 2 and 3
Q4. Consider the following statements regarding the Raja Ramanna Centre for Advanced Technology (RRCAT):
1. It functions under the Department of Atomic Energy.
2. It developed India’s synchrotron radiation facilities Indus-1 and Indus-2.
3. It is located in Visakhapatnam where India’s proton accelerator system will be installed.
(a) 1 and 2 only
(b) 2 only
(c) 1 and 3 only
(d) 1, 2 and 3
Explanation
  • Statement 1 – Correct:
    The Raja Ramanna Centre for Advanced Technology (RRCAT) is a premier research institute functioning under the Department of Atomic Energy (DAE).
  • Statement 2 – Correct:
    RRCAT developed India’s synchrotron radiation sources Indus-1 and Indus-2, which serve as national research facilities for advanced materials, physics, chemistry, and life sciences.
  • Statement 3 – Incorrect:
    RRCAT is located in Indore, Madhya Pradesh, not in Visakhapatnam. Visakhapatnam has been selected as the site for the high-energy proton accelerator system, but the project is being developed by RRCAT.
RRCAT also conducts advanced research in lasers, particle accelerators, and synchrotron radiation technologies, and supports applications such as electron-beam sterilization of medical devices.
Correct Answer: (a) 1 and 2 only
Q5. With reference to the phenomenon of “Black Rain”, consider the following statements:
1. It results when precipitation scavenges soot and other combustion particles suspended in the atmosphere.
2. It forms only when radioactive fallout mixes with precipitation after nuclear explosions.
3. It occurs only when sulfur dioxide emissions convert rainfall into sulfuric acid.
4. It is produced when water vapour condenses directly on hydrocarbon aerosols without cloud formation.
(a) 1 only
(b) 2 only
(c) 1 and 4 only
(d) 2 and 3 only
Explanation
Statement 1 – Correct
Black rain occurs when raindrops pass through polluted air containing soot, ash, hydrocarbons and particulate matter released from large fires, refinery explosions, oil facility fires, wildfires or volcanic eruptions. The falling droplets scavenge these particles, making the rain appear dark or oily.
Statement 2 – Incorrect
Black rain is not restricted to nuclear fallout. The Hiroshima bombing produced a well-known case, but similar phenomena occur after industrial fires and large combustion events.
Statement 3 – Incorrect
This statement describes acid rain, which forms when sulfur dioxide and nitrogen oxides produce sulfuric and nitric acids in precipitation. Acid rain does not necessarily appear black.
Statement 4 – Incorrect
Black rain does not require condensation on hydrocarbon aerosols or the absence of clouds. It occurs through pollutant scavenging by falling raindrops, a common atmospheric process.
Correct Answer: (a) 1 only

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