Nuclear Physics

31. Which of the following diagnostic tests carry the health risks associa

Which of the following diagnostic tests carry the health risks associated with ionizing radiations?

CT scans and X-rays only
MRI scans and X-rays only
CT scans, MRI scans and Ultrasonography only
CT scans, MRI scans, Ultrasonography and X-rays
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UPSC Geoscientist – 2022
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CT scans and X-rays are diagnostic tests that carry health risks associated with ionizing radiations.
Ionizing radiation, such as X-rays and gamma rays, has enough energy to remove tightly bound electrons from atoms, creating ions. This process can damage DNA in cells, potentially leading to an increased risk of cancer over time, especially with repeated exposure. CT scans use multiple X-ray images.
MRI scans use strong magnetic fields and radio waves, which are non-ionizing forms of radiation and do not cause DNA damage in the same way as X-rays. Ultrasonography uses sound waves, also a non-ionizing form of energy. Medical professionals carefully weigh the diagnostic benefits of procedures involving ionizing radiation against the potential risks.

32. The process that is responsible for the generation of energy within th

The process that is responsible for the generation of energy within the core of the sun is:

Nuclear fission
Nuclear fusion
Atomic collision
Atomic excitation
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UPSC Geoscientist – 2021
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The primary process responsible for generating the immense energy within the core of the sun is nuclear fusion. Specifically, it is the fusion of hydrogen nuclei into helium nuclei under extremely high temperatures and pressures.
Nuclear fusion is a process where light atomic nuclei combine to form a heavier nucleus, releasing a large amount of energy. In the Sun, this process is primarily the proton-proton chain, where four hydrogen nuclei (protons) ultimately fuse to form one helium nucleus.
Nuclear fission is the splitting of heavy atomic nuclei, typically used in nuclear power plants. Atomic collision and excitation are processes involving electrons changing energy levels, which can release energy but are not the main source of power for stars.

33. Rutherford’s α-particle scattering experiment was responsible for the

Rutherford’s α-particle scattering experiment was responsible for the discovery of:

Atomic nucleus
Electron
Proton
Neutron
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UPSC Geoscientist – 2021
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Ernest Rutherford’s alpha-particle scattering experiment (also known as the Geiger-Marsden experiment) involved firing alpha particles at a thin gold foil. The results (most particles passing through, some deflected, and a few bouncing back) led Rutherford to propose the nuclear model of the atom, where a tiny, dense, positively charged nucleus exists at the center, with electrons orbiting around it. This experiment was pivotal in the discovery of the atomic nucleus.
Rutherford’s alpha-scattering experiment demonstrated the existence of a small, dense, positively charged region at the center of the atom, which he called the nucleus.
The electron was discovered by J.J. Thomson using cathode ray tubes. Protons were identified as the positive particles within the nucleus, though Rutherford’s experiments were key to understanding the positive charge concentration. Neutrons were discovered later by James Chadwick.

34. Which one of the following statements about the properties of neutrons

Which one of the following statements about the properties of neutrons is not correct?

Neutron mass is almost equal to proton mass.
Neutrons possess zero charge.
Neutrons are located inside the atomic nuclei.
Neutrons revolve around the atomic nuclei.
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UPSC CDS-2 – 2020
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The statement that neutrons revolve around the atomic nuclei is not correct.
Neutrons are fundamental particles found in the nucleus of atoms (with the exception of the most common isotope of hydrogen). They are electrically neutral, possessing zero charge. Their mass is very close to that of a proton, slightly greater but often considered almost equal for simplicity. Protons and neutrons collectively form the atomic nucleus, which is located at the center of the atom. Electrons, which are negatively charged particles, revolve around the atomic nucleus in specific energy levels or orbitals.
The nucleus contains most of the atom’s mass. The number of neutrons in the nucleus determines the isotope of an element. The strong nuclear force binds protons and neutrons together in the nucleus, overcoming the electrostatic repulsion between protons.

35. Rutherford’s alpha particle scattering experiment on thin gold foil wa

Rutherford’s alpha particle scattering experiment on thin gold foil was responsible for the discovery of –

electron
proton
atomic nucleus
neutron
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UPSC CDS-2 – 2019
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Rutherford’s alpha particle scattering experiment, also known as the Geiger–Marsden experiment, involved firing alpha particles at a thin sheet of gold foil. The observation that a small fraction of the alpha particles were deflected at large angles, and some even bounced back, indicated the presence of a small, dense, positively charged core within the atom. This led to the development of the nuclear model of the atom and the discovery of the atomic nucleus.
The key outcome of the experiment was the conclusion that the positive charge and most of the mass of an atom are concentrated in a tiny region at its center, which was named the nucleus.
The electron was discovered by J.J. Thomson through his cathode ray experiments. Protons were later identified as the positively charged particles within the nucleus, and neutrons were discovered by James Chadwick. Rutherford’s experiment was crucial in overturning the earlier plum pudding model of the atom.

36. Consider the following statements: 1. The chain reaction process is

Consider the following statements:

  • 1. The chain reaction process is used in nuclear bombs to release a vast amount of energy, but in nuclear reactors, there is no chain reaction.
  • 2. In a nuclear reactor, the reaction is controlled, while in nuclear bombs, the reaction is uncontrolled.
  • 3. In a nuclear reactor, all operating reactors are ‘critical’, while there is no question of ‘criticality’ in case of a nuclear bomb.
  • 4. Nuclear reactors do not use moderators, while nuclear bombs use them.

Which of the above statements about operational principles of a nuclear reactor and a nuclear bomb is/are correct?

1 and 3
2 and 3
4 only
1 and 4
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UPSC CDS-2 – 2017
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Statement 2 is correct: Nuclear reactors operate under controlled chain reactions, while nuclear bombs involve uncontrolled chain reactions. Statement 3 is also considered correct in this context, highlighting the difference in operation: reactors maintain a controlled ‘critical’ state, while bombs rapidly achieve an uncontrolled ‘supercritical’ state, distinct from sustained critical operation.
The fundamental difference is control: a reactor controls the neutron population to sustain a steady chain reaction, while a bomb allows the neutron population to grow exponentially and uncontrollably.
Statement 1 is incorrect; both use chain reactions. Statement 4 is incorrect; nuclear reactors *do* use moderators (like water, heavy water, or graphite) to slow down neutrons, which is necessary for fission in materials like U-235, whereas nuclear bombs typically use fast neutrons and do not use moderators. Statement 3 is slightly awkwardly phrased, as criticality is essential to both, but the *way* criticality is achieved and maintained (controlled vs. uncontrolled, sustained vs. rapid) is different. Given the options, Statement 3 is intended to represent this difference in operational state relative to criticality.

37. The energy of a photon, whose momentum is 10 MeV/c, where c is the spe

The energy of a photon, whose momentum is 10 MeV/c, where c is the speed of light, is given by

10 MeV
100 MeV
1 MeV
0·1 MeV
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UPSC CDS-2 – 2016
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For a photon, which is a massless particle, the relationship between energy (E) and momentum (p) is given by the equation E = pc, where c is the speed of light. Given the momentum p = 10 MeV/c, the energy E is calculated by multiplying the momentum by c.
The energy (E) and momentum (p) of a photon are related by the formula E = pc.
In this calculation, the unit of momentum is given in a form (MeV/c) that directly leads to the energy unit (MeV) when multiplied by c. The MeV unit (Mega-electron Volt) is a unit of energy commonly used in particle physics. 1 MeV = 1.602 x 10⁻¹³ Joules.

38. In the gamma decay of a nucleus

In the gamma decay of a nucleus

the mass number of the nucleus changes whereas its atomic number does not change
the mass number of the nucleus does not change whereas its atomic number changes
both the mass number and the atomic number of the nucleus change
neither the mass number nor the atomic number of the nucleus changes
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UPSC CDS-2 – 2016
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In the gamma decay of a nucleus, neither the mass number nor the atomic number of the nucleus changes.
– Gamma decay is a type of radioactive decay where an atomic nucleus in an excited state emits a gamma ray photon.
– A gamma ray is high-energy electromagnetic radiation and has no mass or charge.
– The emission of a gamma ray allows the nucleus to transition from a higher energy level to a lower energy level.
– Since no particles (protons or neutrons) are emitted or transformed, the number of protons (atomic number, Z) and the total number of nucleons (mass number, A) in the nucleus remains unchanged.
– Alpha decay decreases A by 4 and Z by 2. Beta decay increases Z by 1 (β⁻ decay) or decreases Z by 1 (β⁺ decay) while A remains unchanged.
Gamma decay often occurs after alpha or beta decay, when the daughter nucleus is left in an excited state. The excited nucleus de-excites by emitting one or more gamma rays.

39. The rest mass of Higgs boson is estimated to be close to

The rest mass of Higgs boson is estimated to be close to

0.5 MeV
900 MeV
100 GeV
1000 GeV
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UPSC CDS-1 – 2024
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The rest mass of the Higgs boson is estimated to be close to 100 GeV.
The Higgs boson was discovered at CERN’s Large Hadron Collider (LHC) in 2012. Experimental measurements determined its mass to be approximately 125 GeV/c². Of the given options, 100 GeV is the closest value.
MeV (Mega-electronvolt) and GeV (Giga-electronvolt) are units of energy commonly used in particle physics, where mass is often expressed using the mass-energy equivalence E=mc². 1 GeV = 1000 MeV. The given options represent masses in the range of MeV and GeV. 0.5 MeV is too small (closer to the mass of an electron), 900 MeV is closer to the mass of a proton or neutron, 100 GeV is in the correct ballpark for the Higgs boson, and 1000 GeV (1 TeV) is much higher.

40. Which of the following particles are subatomic particles? 1. Electron

Which of the following particles are subatomic particles?
1. Electron
2. Proton
3. Neutron
4. Muon
Select the correct answer using the code given below.

1 and 4 only
1, 2, 3 and 4
2 and 3 only
1, 2 and 3 only
This question was previously asked in
UPSC CDS-1 – 2024
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All the listed particles – Electron, Proton, Neutron, and Muon – are considered subatomic particles.
Subatomic particles are particles that are smaller than an atom.
– Electrons are fundamental particles (leptons) that orbit the nucleus of an atom.
– Protons and Neutrons are found in the nucleus of an atom. They are composite particles, each made up of three quarks (protons are two up quarks and one down quark, neutrons are one up quark and two down quarks). Despite being composite, they are typically classified as subatomic particles.
– Muons are fundamental particles (leptons), similar to electrons but much more massive. They are not constituents of ordinary atoms but are produced in high-energy interactions.
Subatomic particles can be fundamental (like electrons, muons, quarks, neutrinos, photons) or composite (like protons, neutrons, which are made of quarks). All particles smaller than an atom fall under the broad category of subatomic particles.
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