Nuclear Physics

1. Which one of the following is the energy source of stars ?

Which one of the following is the energy source of stars ?

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Nuclear fission
Nuclear fusion
Chemical reaction
Photochemical reaction
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UPSC CISF-AC-EXE – 2023
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The correct answer is B.
Stars generate energy primarily through nuclear fusion reactions in their core. Specifically, in stars like our Sun, hydrogen nuclei fuse to form helium nuclei, releasing a vast amount of energy according to Einstein’s mass-energy equivalence principle (E=mc²).
Nuclear fission is the process of splitting heavy atomic nuclei, used in nuclear power plants on Earth, but not the main energy source of stars. Chemical reactions involve the rearrangement of electrons and release far less energy than nuclear reactions, insufficient to power a star for its lifetime. Photochemical reactions are triggered by light, not the primary energy generation mechanism in the core of a star.

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2. The efforts to detect the existence of Higgs boson particle have becom

The efforts to detect the existence of Higgs boson particle have become frequent news in the recent past. What is/are the importance/importances of discovering this particle?

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  • 1. It will enable us to understand as to why elementary particles have mass.
  • 2. It will enable us in the near future to develop the technology of transferring matter from one point to another without traversing the physical space between them.
  • 3. It will enable us to create better fuels for nuclear fission.

Select the correct answer using the codes given below.

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1 only
2 and 3 only
1 and 3 only
1, 2 and 3
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UPSC IAS – 2013
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Statement 1 is correct because the Higgs boson is fundamentally linked to the mechanism by which elementary particles acquire mass through their interaction with the Higgs field. Statements 2 and 3 are incorrect; the discovery of the Higgs boson is not related to matter transfer technology (teleportation) or nuclear fission fuel development.
The Standard Model of particle physics describes the fundamental particles and forces. The Higgs field and its associated particle, the Higgs boson, were proposed to explain why some elementary particles have mass while others (like photons) do not. The detection of the Higgs boson in 2012 by the ATLAS and CMS experiments at CERN’s Large Hadron Collider confirmed this mechanism.
Statement 2 describes a speculative concept (teleportation) not related to the properties or applications of the Higgs boson. Statement 3 is irrelevant to the field of nuclear energy; nuclear fission involves the splitting of atomic nuclei, a process governed by the strong nuclear force and properties of isotopes, not the Higgs mechanism.

3. The known forces of nature can be divided into four classes, viz., gra

The known forces of nature can be divided into four classes, viz., gravity, electromagnetism, weak nuclear force and strong nuclear force. With reference to them, which one of the following statements is not correct?

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Gravity is the strongest of the four
Electromagnetism acts only on particles with an electric charge
Weak nuclear force causes radioactivity
Strong nuclear force holds protons and neutrons inside the nucleus of an atom
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UPSC IAS – 2013
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The statement that Gravity is the strongest of the four fundamental forces is not correct.
The four fundamental forces of nature are, in order of decreasing strength: Strong Nuclear Force, Electromagnetic Force, Weak Nuclear Force, and Gravity. Gravity is by far the weakest of the four forces. The Strong Nuclear Force holds the nucleus together, Electromagnetism governs interactions between charges, and the Weak Nuclear Force is involved in radioactive decay.
Although gravity is the weakest force at the particle level, its effects are cumulative and always attractive. This makes it the dominant force on large astronomical scales (planets, stars, galaxies). The relative strengths of the forces are approximately: Strong Nuclear Force ~ 1, Electromagnetic Force ~ 10⁻², Weak Nuclear Force ~ 10⁻⁶, Gravity ~ 10⁻³⁹ (relative to the strong force at typical nuclear scales).

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4. An electron and a photon have same de Broglie wavelength. It implies t

An electron and a photon have same de Broglie wavelength. It implies that they have the same

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linear momentum
energy
speed
angular momentum
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UPSC CAPF – 2020
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If an electron and a photon have the same de Broglie wavelength (λ), it implies that they have the same linear momentum.
The de Broglie wavelength is given by the formula λ = h/p, where h is Planck’s constant and p is the linear momentum. If λ is the same and h is constant, then p must be the same.
While their momentum is the same, their energy and speed are generally different. For a photon, energy E = pc and speed is c. For an electron with mass m and speed v, momentum p = mv (non-relativistic) and kinetic energy KE = p^2/(2m). Same momentum p does not mean same energy or speed due to the difference in their mass and the relativistic nature of the photon.

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5. The number of neutrons inside the nucleus of the element Uranium-235

The number of neutrons inside the nucleus of the element Uranium-235 is

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235
92
143
51
This question was previously asked in
UPSC CAPF – 2019
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The number 235 in Uranium-235 is the mass number (A), which is the total number of protons and neutrons in the nucleus. Uranium (U) has an atomic number (Z) of 92, meaning it has 92 protons. The number of neutrons (N) is calculated by subtracting the atomic number from the mass number: N = A – Z.
– Mass number (A) = Number of protons + Number of neutrons.
– Atomic number (Z) = Number of protons.
– For Uranium-235, A = 235 and Z = 92.
– Number of neutrons = 235 – 92 = 143.
– Uranium has several isotopes, including Uranium-238 (most common, 146 neutrons) and Uranium-235 (used in nuclear reactors and weapons, 143 neutrons).

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6. The mass number of an element is NOT changed when it emits

The mass number of an element is NOT changed when it emits

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Alpha and Beta radiations only
Alpha and Gamma radiations only
Beta and Gamma radiations only
Alpha, Beta and Gamma radiations
This question was previously asked in
UPSC CAPF – 2017
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The mass number (A) of an element is the total number of protons and neutrons in the nucleus.
– Alpha (α) decay: Emits a ⁴₂He nucleus. The mass number decreases by 4.
– Beta (β) decay (β⁻ or β⁺ or electron capture): In β⁻ decay, a neutron turns into a proton (A remains same, Z increases by 1). In β⁺ decay, a proton turns into a neutron (A remains same, Z decreases by 1). In electron capture, a proton captures an electron to become a neutron (A remains same, Z decreases by 1). In all Beta decay processes, the mass number does NOT change.
– Gamma (γ) decay: Emits a high-energy photon. This occurs when a nucleus transitions from a higher energy state to a lower energy state. Neither the atomic number (Z) nor the mass number (A) changes during gamma decay.
Therefore, the mass number is NOT changed when Beta and Gamma radiations are emitted.
Alpha decay changes both atomic number and mass number. Beta and Gamma decay do not change the mass number.
Radioactive decay processes result in the transformation of one atomic nucleus into another or into a lower energy state. The type of decay determines how the atomic number and mass number of the nucleus change.

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7. In a radioactive decay of a nucleus, an electron is also emitted. This

In a radioactive decay of a nucleus, an electron is also emitted. This may happen due to the fact that :

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electrons are present inside a nucleus
an electron is created at the time of conversion of a neutron into proton
an electron is created at the time of conversion of a proton into a neutron
electrons need to be emitted for conservation of momentum
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UPSC CAPF – 2015
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In radioactive beta minus (β⁻) decay, an electron is emitted because a neutron is converted into a proton within the nucleus.
Beta minus (β⁻) decay is a type of radioactive decay in which a neutron (n) within an atomic nucleus is converted into a proton (p). In this process, an electron (e⁻) and an electron antineutrino (ν̄e) are emitted from the nucleus. The reaction is typically written as: n → p + e⁻ + ν̄e. The electron is not pre-existing within the nucleus; it is created during this transformation. The atomic number of the nucleus increases by one, while the mass number remains unchanged.
Electrons are fundamental particles and are not constituents of the nucleus; protons and neutrons are the nucleons. The electron emitted in beta decay originates from the conversion of a neutron. Another type of beta decay is beta plus (β⁺) decay, where a proton converts into a neutron, emitting a positron (e⁺) and an electron neutrino (νe): p → n + e⁺ + νe. Electron capture is an alternative process where an electron from an inner atomic shell is captured by a proton in the nucleus, leading to the conversion of a proton into a neutron and emission of a neutrino. Momentum and energy conservation rules are followed in all radioactive decay processes, and the emission of the neutrino/antineutrino is necessary for conserving energy, momentum, and angular momentum, but the *reason* for electron emission in β⁻ decay is the fundamental weak interaction process of neutron decay.

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8. γ-ray consists of :

γ-ray consists of :

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meson particles
neutrino particles
Higg's boson
electromagnetic waves
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UPSC CAPF – 2015
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γ-ray consists of electromagnetic waves. Gamma rays are a form of electromagnetic radiation with the shortest wavelengths and highest frequencies, and therefore highest photon energies. They are part of the electromagnetic spectrum, like visible light or X-rays, but with much higher energy.
Unlike alpha and beta radiation which consist of particles, gamma radiation consists of energy packets (photons) and is an electromagnetic wave.
Gamma rays are typically produced by the decay of atomic nuclei (radioactive decay) or other high-energy processes like electron-positron annihilation. Mesons, neutrinos, and Higgs bosons are types of elementary particles, not constituents of gamma radiation.

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9. Movement of outer electrons in the inner orbits of an atom produces :

Movement of outer electrons in the inner orbits of an atom produces :

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α-ray
β-ray
γ-ray
x-ray
This question was previously asked in
UPSC CAPF – 2015
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Movement of outer electrons in the inner orbits of an atom produces X-rays. When high-energy electrons bombard a target material, they can knock out inner-shell electrons of the target atoms. The vacancies are then filled by electrons from higher energy levels (outer orbits) transitioning to the inner orbits, emitting photons in the process. If the energy difference is large enough, these photons are in the X-ray region of the electromagnetic spectrum.
X-rays are produced when electrons transition between energy levels in the inner shells of atoms or when charged particles are decelerated rapidly (bremsstrahlung). The question specifically refers to electron transitions from outer to inner orbits, which is a mechanism for characteristic X-ray emission.
α-rays are streams of alpha particles (helium nuclei). β-rays are streams of beta particles (electrons or positrons). γ-rays are high-energy electromagnetic waves produced by nuclear transitions. These are fundamentally different from the process described in the question, which relates to electron transitions within the atom’s electron cloud.

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10. In January 2015, Government of India approved the establishment of a N

In January 2015, Government of India approved the establishment of a Neutrino Observatory at :

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Bodi hills in Tamil Nadu
Kaina hills in Manipur
Jampui hills in Tripura
Nallamala hills in Andhra Pradesh
This question was previously asked in
UPSC CAPF – 2015
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In January 2015, the Government of India approved the establishment of a Neutrino Observatory at Bodi hills in Tamil Nadu.
The India-based Neutrino Observatory (INO) project received Union Cabinet approval in January 2015 for setting up a mega-science laboratory to study neutrinos. The approved site is in the Bodi West Hills, in the Theni district of Tamil Nadu.
Neutrino observatories are typically located underground to shield the detectors from cosmic rays and other background noise, allowing for the precise detection of neutrinos. The INO project aims to build a large underground detector to study atmospheric neutrinos and potentially solar neutrinos.

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