Nuclear Physics is part of Physics. Below are notes on 12 sub-topics, followed by practice MCQs from State PSC and UPSC papers.

Basic properties of nuclei: size, shape, charge, mass, spin, magnetic dipole and electric quadrupole moments.

  • Atomic Structure Basics: An atom consists of a central, dense nucleus and electrons orbiting it.
  • Nucleus Composition: The atomic nucleus is composed of protons and neutrons (collectively called nucleons).
  • Protons: Carry a positive charge (+e), located in the nucleus.
  • Neutrons: Electrically neutral (zero charge), located in the nucleus. Neutron mass is approximately equal to proton mass. Discovered by Chadwick.
  • Electrons: Carry a negative charge (-e), orbit the nucleus in specific energy levels/shells.
  • Atomic Number (Z): Number of protons in the nucleus. Determines the element.
  • Mass Number (A): Total number of protons and neutrons in the nucleus (A = Z + N). Represents the approximate total mass of the nucleus in atomic mass units (amu).
  • Number of Neutrons (N): N = A - Z.
  • Hydrogen Nucleus: Protium (¹H₁) contains one proton and zero neutrons. Deuterium (²H₁) has one proton and one neutron. Tritium (³H₁) has one proton and two neutrons (Atomic number is 1 for all Hydrogen isotopes).
  • Plutonium-242 (₂₄₂Pu₉₄): Has 94 protons and 242 - 94 = 148 neutrons.
  • Uranium-235 (₂₃₅U₉₂): Has 92 protons and 235 - 92 = 143 neutrons.
  • Helium Nucleus (Alpha particle, ⁴He₂): Contains two protons and two neutrons. It carries two positive charges. Its mass is very nearly equal to that of a helium atom.
  • Nuclear Size: Nuclei are very small (radius ~10⁻¹⁵ m, femtometers or fermis) compared to atoms (~10⁻¹⁰ m). Nuclear radius (R) is approximately R = R₀A^(1/3), where R₀ ≈ 1.2 fm and A is the mass number.
  • Nuclear Shape: Most nuclei are approximately spherical. Some nuclei exhibit deformed (e.g., ellipsoidal) shapes.
  • Nuclear Charge: The total charge of a nucleus is +Ze, where Z is the atomic number and e is the elementary positive charge.
  • Nuclear Mass: The vast majority of an atom's mass is concentrated in its nucleus. Nuclear mass is slightly less than the sum of individual masses of its constituent protons and neutrons (mass defect).
  • Nuclear Spin (I): Nuclei possess an intrinsic angular momentum called nuclear spin, which is a quantum mechanical property arising from the spins and orbital angular momenta of its nucleons.
  • Magnetic Dipole Moment (μ): Nuclei with non-zero spin have a magnetic dipole moment due to the motion and intrinsic spins of their charged constituents (protons). This property is utilized in Nuclear Magnetic Resonance (NMR).
  • Electric Quadrupole Moment (Q): Measures the deviation of a nucleus's charge distribution from perfect spherical symmetry. A spherical nucleus has a zero electric quadrupole moment. A non-zero moment indicates a deformed (e.g., prolate or oblate ellipsoidal) nuclear shape.
  • Rutherford's α-particle scattering experiment:
    • Used a thin gold foil as a target.
    • Led to the discovery of the atomic nucleus: a tiny, dense, positively charged region at the center of the atom.
    • Concluded that most of the atom is empty space.
    • Showed the radius of the atom is about 10⁵ times the radius of the nucleus.
    • Did not explain the stability of atoms or electron orbits (which Bohr later addressed).
  • J.J. Thomson's Plum Pudding Model: Proposed that an atom is a uniform sphere of positive charge with electrons embedded in it. Explained the overall neutrality of atoms but failed to explain scattering results or stability.
  • Isotopes: Atoms of the same element (same Z, same number of protons) but with different mass numbers (A), meaning different numbers of neutrons. (e.g., Protium, Deuterium, Tritium are isotopes of Hydrogen).
  • Isobars: Atoms with the same mass number (A) but different atomic numbers (Z), hence different elements. (e.g., ⁴⁰K₁₉ and ⁴⁰Ca₂₀ have A=40). Examples from MCQs: ²⁴Mg₁₂ and ²⁴Na₁₁ are isobars.
  • Isodiaphers: Nuclides with the same neutron excess (N-Z) or (A-2Z).
  • Neutrino: A subatomic particle with very small (or zero) mass and zero electric charge.
  • Nuclear Physics: The branch of physics that deals with the study of atomic nuclei.
  • Moseley's Law: States that the square root of the frequency of X-ray spectral lines is proportional to (Z-b), where Z is the atomic number. This law established the concept of atomic number as a fundamental property for ordering elements in the periodic table.
  • Ionization Energy of Hydrogen: The energy required to remove an electron from a hydrogen atom in its ground state is 13.6 eV.
  • India's Nuclear Fuel: India's long-term nuclear energy plans are based on Thorium, which is abundant in monazite sands.
  • Word "Atom": From a Greek word meaning "uncuttable" or "indivisible."

Binding energy, mass defect, packing fraction, semi-empirical mass formula (Weizsäcker formula) and its applications.

Mass Defect (Δm): The difference between 1. the sum of the masses of individual constituent nucleons (protons and neutrons) and the actual mass of the nucleus.

    • Δm = [Zmₚ + (A-Z)mₙ] - M(A,Z)
    • Z = atomic number (protons), A = mass number (protons + neutrons), mₚ = proton mass, mₙ = neutron mass, M(A,Z) = nuclear mass. Binding Energy (BE): The energy equivalent 2. of the mass defect (Δm), calculated using Einstein's mass-energy equivalence relation E=mc².
    • BE = (Δm)c²
    • It is the energy required to break a nucleus into its constituent nucleons.
    • It is also the energy made available when free nucleons combine to form a stable nucleus.
    • Energy equivalent of 1 gram substance (using E=mc²): 9 x 10¹³ Joules ≈ 5.618 x 10²⁶ MeV. Binding Energy per Nucleon (BE/A): Total 3. binding energy divided by the mass number (A).
    • Higher BE/A indicates greater nuclear stability.
    • Energy released in nuclear reactions (like fission or fusion) = (Total BE of products) - (Total BE of reactants).
    • Example (MCQ 1): For ²⁴⁰U (BE/ A=7.6 MeV) disintegrating into two ¹²⁰Sn (BE/A=8.4 MeV):
      • BE of ²⁴⁰U = 240 7.6 MeV = 1824 MeV.
      • Total BE of two ¹²⁰Sn = 2 (120 8.4 MeV) = 2 1008 MeV = 2016 MeV.
      • Energy released = 2016 MeV 1824 MeV = 192 MeV. Packing Fraction (f): (M - A) / A, where M is 4. the exact isotopic mass and A is the mass number.
    • A measure of nuclear stability.
    • Negative packing fraction implies the nucleus is more stable than the reference (e.g., carbon-12).
    • Positive packing fraction implies the nucleus is less stable.
    • A smaller magnitude (closer to zero) indicates greater stability. Semi-Empirical Mass Formula (Weizsäcker 5. Formula): An approximate formula for calculating the binding energy of an atomic nucleus, based on the liquid drop model and empirical observations.
    • BE = aᵥA - aₛA^(2/3) - ac Z(Z-1)/ A^(1/3) - aa (A-2Z)²/A ± ap A^(-3/4)
    • Components (and their effect on BE): Volume Term (aᵥA): Positive, 1. due to attractive strong nuclear force; proportional to volume (A). Surface Term (-aₛA^(2/3)): Neg2. ative, nucleons on the surface are less bound; proportional to surface area (A^(2/3)). Coulomb Term (-ac Z(Z-1)/ 3. A^(1/3)): Negative, due to electrostatic repulsion between protons; proportional to Z(Z-1) and inversely to radius. Asymmetry Term (-aa (A-2Z)²/ 4. A): Negative, favors stability for N≈Z (equal protons and neutrons). Pairing Term (± ap A^(-3/4)): 5. Positive for even-even nuclei (most stable), negative for oddodd (least stable), zero for oddeven/even-odd.
    • Applications:
      • Predicts nuclear masses and binding energies.
      • Explains nuclear stability and the binding energy per nucleon curve.
      • Provides insights into nuclear fission and alpha decay. Historical & Institutional Context: 6.
    • Ernest Rutherford: Initially expressed skepticism about the practical generation of nuclear power, not due to doubting E=mc² but due to the perceived difficulty in achieving a sustained nuclear chain reaction.
    • Homi J. Bhabha: First Chairman of the Atomic Energy Commission of India (established 1948). The Homi Bhabha award is given for special contributions in the field of Nuclear Energy.

Conservation laws in particle physics (baryon number, lepton number, strangeness, isospin, parity).

  • Baryon Number (B):
    • Quantum number for baryons (protons, neutrons, etc.) and antibaryons.
    • B = +1 for baryons, B = -1 for antibaryons, B = 0 for mesons, leptons, photons.
    • Strictly conserved in strong, electromagnetic, and weak interactions.
  • Lepton Number (L):
    • Quantum number for leptons (electron, muon, tau, and their neutrinos) and antileptons.
    • L = +1 for leptons, L = -1 for antileptons, L = 0 for hadrons, photons.
    • Three separate lepton numbers: electron lepton number (Le), muon lepton number (Lμ), tau lepton number (Lτ).
    • Each Le, Lμ, Lτ is conserved independently in all known interactions. Total lepton number (L = Le + Lμ + Lτ) is also conserved.
  • Strangeness (S):
    • Quantum number associated with the strange quark (s) and anti-strange quark (s̅ ).
    • S = -1 for s quark, S = +1 for s̅ antiquark.
    • Conserved (ΔS = 0) in strong and electromagnetic interactions.
    • Violated (ΔS = ±1) in weak interactions.
  • Isospin (I or I3):
    • Quantum number reflecting the charge independence of the strong nuclear force (symmetry between up and down quarks).
    • For a multiplet, I is fixed; I3 (third component) distinguishes members (e.g., proton I3 = +1/2, neutron I3 = -1/2).
    • Conserved (ΔI = 0, ΔI3 = 0) in strong interactions.
    • Violated in electromagnetic and weak interactions.
  • Parity (P):
    • Quantum number describing the behavior of a particle's wavefunction under spatial inversion (mirror reflection) (x,y,z → -x,-y,-z).
    • Intrinsic parity is an attribute of a particle, usually +1 or -1.
    • Conserved in strong and electromagnetic interactions.
    • Violated in weak interactions (discovered by C. N. Yang and T. D. Lee, confirmed by C. S. Wu experiment).

Elementary particles: classification (leptons, hadrons, quarks), fundamental interactions (strong, weak, electromagnetic, gravitational).

  • Elementary Particles Classification:
    • Leptons: Fundamental particles, not subject to strong force. Spin 1/2 (fermions).
      • Examples: Electron (negatively charged, constituent of cathode rays, mass much less than proton), Muon, Tau, and their corresponding Neutrinos.
      • Neutrinos: Have near-zero mass.
      • Positron: Anti-electron, a lepton, has spin 1/2 (fractional spin).
    • Hadrons: Composite particles made of quarks, affected by strong force.
      • Baryons: Composed of three quarks (e.g., Proton (uud), Neutron (udd)). Proton and Neutron are subatomic particles.
      • Mesons: Composed of a quarkantiquark pair.
    • Quarks: Fundamental particles. Spin 1/2 (fermions).
      • Possess fractional electric charge (+2/3e or -1/3e).
      • Six "flavors": up, down, charm, strange, top, bottom. Never observed in isolation (quark confinement).
    • Bosons (Force Carriers): Have integral spin (0, 1, 2).
      • Photon: Mediator of electromagnetic force, zero rest mass, spin 1.
      • Gluon: Mediator of strong force, zero rest mass, spin 1.
      • W and Z bosons: Mediators of weak force, massive, spin 1.
      • Higgs Boson: Scalar boson (spin 0). Responsible for giving mass to elementary particles via the Higgs field. Mass approx. 125 GeV. Its discovery does not discard Einstein's Special Theory of Relativity.
      • Graviton: Hypothetical mediator of gravitational force, zero rest mass, spin 2.
  • Fundamental Interactions (Forces):
    • Strong Nuclear Force:
      • Strongest force in nature.
      • Range: Very short (~10-15 m, nuclear distances).
      • Mediator: Gluon.
      • Role: Binds quarks into hadrons (protons, neutrons); holds protons and neutrons in the atomic nucleus.
    • Electromagnetic Force:
      • Second strongest force.
      • Range: Infinite.
      • Mediator: Photon.
      • Role: Acts only on electrically charged particles. Responsible for atomic structure, chemical bonds, light. Deflects charged particles in electric and magnetic fields.
    • Weak Nuclear Force:
      • Third strongest force.
      • Range: Very short (~10-18 m).
      • Mediator: W and Z bosons.
      • Role: Causes radioactive decay (e.g., beta decay).
    • Gravitational Force:
      • Weakest force in nature.
      • Range: Infinite.
      • Mediator: Graviton (hypothetical).
      • Role: Acts on all particles with mass/energy. Dominant on cosmological scales.
  • Key Facts:
    • Subatomic particles include Electron, Proton, Neutron, and Muon. Deuteron is a nucleus (a composite particle), not an elementary subatomic particle.
    • Electron is negatively charged, a constituent of cathode rays, and is deflected by both electric and magnetic fields. Its mass is much smaller than a proton's.
    • The OPERA experiment (2011) initially claimed neutrinos moved faster than light at a European Laboratory in Geneva, but this finding was later retracted. Such a discovery would have gone against Einstein's Special Theory of Relativity.
    • China is building the world's largest neutrino-detecting telescope, "Trident".
    • India-based Neutrino Observatory (INO) was approved for establishment at Bodi hills in Tamil Nadu in January 2015.

Nature of nuclear force: characteristics, deuteron problem, meson theory (Yukawa potential).

  • Characteristics of Nuclear Force:
    • Strongest fundamental force: Approximately 100x stronger than electromagnetic, 10^6x stronger than weak, 10^38x stronger than gravitational force.
    • Short-range: Effective only over very small distances, typically ~1-2 femtometers (fm). Beyond 2-3 fm, force drops to negligible values.
    • Attractive at intermediate distances (0.5 to 2 fm), responsible for binding nucleons together.
    • Repulsive at very short distances (<0.5 fm), preventing nuclear collapse.
    • Charge-independent (approximately): Strength is nearly the same for p-p, nn, and n-p interactions (after accounting for Coulomb repulsion in p-p).
    • Spin-dependent: Stronger when nucleon spins are parallel; weaker when anti-parallel.
    • Saturating nature: Each nucleon interacts only with a limited number of its closest neighbors (explains the nearconstant binding energy per nucleon for nuclei with A > 20).
    • Non-central / Tensor component: Not purely radial; depends on the relative orientation of nucleon spins and their position vector.
  • Deuteron Problem:
    • The deuteron (one proton, one neutron) is the simplest bound nuclear system.
    • Its observed properties (binding energy, spin, magnetic dipole moment, electric quadrupole moment) are crucial for deducing characteristics of the nuclear force.
    • The non-zero electric quadrupole moment of the deuteron provides direct evidence for the non-central (tensor) component of the nuclear force.
    • The deuteron's spin of 1 indicates parallel spins of the proton and neutron, supporting the spin-dependence of the nuclear force.
  • Meson Theory (Yukawa Potential):
    • Proposed by Hideki Yukawa (1935) to explain the nuclear force.
    • Nuclear force arises from the exchange of virtual particles called mesons (specifically, pions, π mesons).
    • Pion exchange:
      • Charged pions (π+, π-) mediate proton-neutron (p ↔ n + π+) and neutron-proton (n ↔ p + π-) interactions.
      • Neutral pions (π0) mediate proton-proton (p ↔ p + π0) and neutron-neutron (n ↔ n + π0) interactions.
    • Yukawa Potential: V(r) = - (g²/r) e^(-r/ λ)
      • Describes the potential energy between two nucleons.
      • `g` is a coupling constant.
      • `λ = ħ / (mπ c)` is the range parameter, where `mπ` is the mass of the exchanged meson.
      • The finite, short range of the nuclear force is directly related to the finite mass of the exchanged particle (larger mass implies shorter range).
      • Yukawa's theory successfully predicted the existence and approximate mass of these mesons (around 200-300 times the electron mass), later found for pions.

Nuclear fission: theory, chain reaction, critical mass, nuclear reactors (types, components, safety aspects).

  • Nuclear Fission Theory:
  • Nuclear fission is the process where a heavy nucleus (e.g., Uranium-235, Plutonium-239) splits into two or more smaller nuclei, releasing a significant amount of energy.
  • Fission is typically initiated by the absorption of a neutron (usually a slow or thermal neutron for U-235).
  • Heavy initial nuclides suitable for fission generally have a larger number of neutrons than protons.
  • The energy released during nuclear fission is explained by Einstein's mass-energy equivalence principle (E=mc²).
  • Nuclear Fuel:
  • Common nuclear fuels include fissile isotopes like Uranium-235 (U-235), Uranium-233 (U-233), and Plutonium-239 (Pu-239), and fertile materials like Thorium-232 (Th-232) and Uranium-238 (U-238).
  • Uranium-235 is the primary isotope used in most nuclear power plants to produce electricity.
  • Pitchblende (Uraninite) is a significant mineral source of Uranium.
  • Fuel rods in nuclear reactors typically contain ceramic uranium oxide (UO₂) pellets.
  • Lead and Calcium are not used as nuclear fuels.
  • Chain Reaction & Critical Mass:
  • A chain reaction occurs when neutrons released from one fission event trigger further fission events.
  • In nuclear reactors, the chain reaction is controlled to produce energy steadily for electricity generation.
  • In nuclear bombs, the chain reaction is uncontrolled, leading to a rapid and massive release of energy.
  • Critical mass is the minimum amount of fissile material required to sustain a nuclear chain reaction. All operating nuclear reactors are maintained in a 'critical' state.
  • Nuclear Reactor Principles & Components:
  • The basic scientific principle behind a nuclear reactor is controlled nuclear fission.
  • Nuclear reactors generate heat from nuclear fuel to produce steam, which then drives turbines for electricity.
  • Fuel: Contains the fissile material (e.g., U-235) in fuel rods (e.g., UO₂).
  • Moderator: Material (e.g., Heavy water (D₂O), Graphite, Ordinary water) used to slow down the fast neutrons produced during fission to thermal speeds, making them more likely to cause further fission in U-235. Petrol and Diesel are not moderators.
  • Control Rods: Made of neutron-absorbing materials (e.g., Cadmium, Boron) to regulate the rate of the chain reaction.
  • Coolant: A fluid (e.g., water, heavy water, liquid metals) that transfers the heat generated by fission from the reactor core.
  • Shielding: Protective barriers (e.g., concrete, lead) surrounding the reactor core to absorb radiation. Lead is used for safety from nuclear radiation.
  • Heat Exchanger: Transfers heat from the primary coolant to a secondary fluid circuit to produce steam.
  • Turbine: Converts the energy of steam into mechanical energy to drive an electric generator.
  • Reaction Chamber: The core area where nuclear fission occurs.
  • A mechanism to reduce CO₂ emission is not a direct component of a nuclear reactor.
  • In a nuclear reactor system, momentum, energy, and mass are broadly conserved (massenergy conservation).
  • Types of Nuclear Reactors:
  • Pressurized Heavy Water Reactor (PHWR): Uses heavy water as both a moderator and a coolant. Examples in India include Kaiga, Narora (NAPS), and Rawatbhata (RAPS).
  • Boiling Water Reactor (BWR): Uses ordinary water as both moderator and coolant, allowing it to boil within the reactor core to produce steam directly. Example: Tarapur Atomic Power Station (TAPS-1).
  • Pressurized Water Reactor (PWR): Uses ordinary water as moderator and coolant, keeping it under high pressure to prevent boiling. Steam is generated in a separate heat exchanger. Example: Kudankulam Nuclear Power Plant (KKNPP-2, which uses VVER, a type of PWR).
  • Fast Breeder Reactor (FBR): A nuclear reactor that produces more fissile material (e.g., Plutonium-239 from Uranium-238, or Uranium-233 from Thorium-232) than it consumes. FBRs use fast neutrons to sustain the chain reaction and do not require a moderator.
  • India's Nuclear Program & Key Facilities:
  • India's first nuclear reactor was Apsara, built in 1956.
  • KAMINI is India's first large research reactor that uses Uranium-233 as fuel.
  • The Indira Gandhi Centre for Atomic Research (IGCAR) at Kalpakkam operates a Prototype Fast Breeder Reactor (PFBR) to generate electricity and breed new fissile fuel.
  • India utilizes Thorium as a nuclear fuel in its advanced three-stage nuclear power program.
  • Global Context:
  • The world's first floating nuclear power plant was developed by Russia.
  • Nuclear energy is not considered a biomass energy source.

Nuclear fusion: stellar energy processes, controlled thermonuclear fusion.

  • Nuclear fusion is the process where two or more light atomic nuclei combine to form a heavier nucleus, releasing a vast amount of energy.
  • The energy radiated by the Sun and other stars is generated primarily through nuclear fusion processes.
  • In the Sun's core, hydrogen nuclei (primarily protons) fuse to form helium nuclei, releasing energy. This is the main nuclear fuel for the Sun.
  • Nuclear fusion reactions require extremely high temperatures (thermonuclear reactions) and immense pressures to overcome the electrostatic repulsion between positively charged nuclei.
  • An example of a nuclear fusion reaction is the fusion of deuterium and tritium: ²₁H + ³₁H → ⁴₂He + ¹₀n.
  • Controlled thermonuclear fusion aims to harness this energy for electricity generation; it involves maintaining and confining a superheated plasma at very high temperatures.
  • Tokamak is a common design for controlled thermonuclear fusion reactors, employing strong magnetic fields for plasma confinement.
  • The hydrogen bomb is based on an uncontrolled nuclear fusion reaction.
  • In contrast, nuclear fission is the process where a heavy atomic nucleus splits into two or more smaller nuclei, also releasing significant energy.
  • Nuclear fission is typically a neutron-induced nuclear reaction.
  • Nuclear power plants utilize controlled nuclear fission to produce electricity.
  • The atom bomb (or uranium bomb) is based on an uncontrolled nuclear fission reaction.
  • Uranium, due to its large and unstable nucleus, undergoes nuclear fission, not nuclear fusion.
  • Most sources of energy we use on Earth, such as biomass and wind energy, are ultimately derived from the Sun's energy, which originates from nuclear fusion.
  • Nuclear energy (both fission and fusion) and geothermal energy are not ultimately derived from the Sun's energy.

Nuclear reactions: conservation laws, Q-value, cross-section, compound nucleus and direct reactions.

  • Nuclear Reaction: A process in which two nuclei or nuclear particles collide to produce different products, represented as X(a,b)Y or X + a → Y + b.
  • Conservation Laws in Nuclear Reactions:
    • Mass-Energy Conservation: Total relativistic energy (E=mc² + KE) of the system is conserved. Related to the Qvalue.
    • Linear Momentum Conservation: Total linear momentum before and after the reaction is conserved.
    • Angular Momentum Conservation: Total angular momentum (orbital + spin) is conserved.
    • Charge Conservation (Atomic Number Z): The total charge (sum of atomic numbers) remains constant.
    • Nucleon Number Conservation (Mass Number A): The total number of nucleons (protons + neutrons) remains constant for typical low-energy reactions.
    • Parity Conservation: Parity is conserved in strong and electromagnetic interactions.
  • Q-value (Reaction Energy): The energy released or absorbed in a nuclear reaction.
    • Calculated as: Q = (Σmreactants Σmproducts)c².
    • Alternatively: Q = KEproducts - KEreactants.
    • Q > 0 (Exoergic/Exothermic): Energy is released (products have less mass than reactants).
    • Q < 0 (Endoergic/Endothermic): Energy is absorbed (products have more mass than reactants); requires a minimum threshold kinetic energy for the reaction to occur.
  • Reaction Cross-Section (σ): A measure of the probability that a nuclear reaction will occur.
    • Unit: Barn (b); 1 barn = 10⁻²⁸ m².
    • Represents the effective target area presented by the nucleus to the incident particle.
    • Can be total, elastic scattering, inelastic scattering, or reaction crosssections.
  • Compound Nucleus Model (Bohr's Hypothesis):
    • Reaction proceeds in two independent steps: Formation of a highly excited, 1. unstable compound nucleus by the incident particle and target nucleus. Decay of the compound nucleus 2. by emitting particles or gamma rays.
    • Characteristics: Long lifetime (~10⁻¹⁶ to 10⁻¹⁸ s), excitation energy shared among all nucleons, decay modes are independent of formation, often isotropic angular distribution of products.
    • Applicable for low-energy reactions.
  • Direct Reactions:
    • Incident particle interacts directly with one or a few nucleons at the surface of the target nucleus without forming an intermediate compound nucleus.
    • Characteristics: Short lifetime (~10⁻²² s, comparable to transit time), product angular distribution is typically strongly forward-peaked, dependent on the details of the surface interaction.
    • Examples: Stripping (e.g., (d,p)), pickup (e.g., (p,d)), direct inelastic scattering (e.g., (p,p')).
    • Applicable for higher-energy reactions.
  • Photon Energy-Momentum Relation: For a photon, its energy (E) and momentum (p) are related by E = pc, where c is the speed of light. If momentum (p) is expressed in units of MeV/c, then energy (E) will be in MeV.

Particle

accelerators:

Cyclotron,

Synchrocyclotron, Betatron, Synchrotron,

Linear accelerators.

  • Particle Accelerators (General):
    • Purpose: Accelerate charged particles (protons, electrons, ions) to very high kinetic energies.
    • Mechanism: Utilize electric fields for acceleration and magnetic fields for guiding/confining particle paths.
    • Applications: Fundamental research (particle physics), medical (radiation therapy, isotope production), material science.
    • Field: Central to Particle Physics, the branch dealing with very small particles and fundamental interactions.
    • Energy-Momentum Relationship: Kinetic Energy (KE) gained by particle with charge `q` accelerated by potential difference `V` is `KE = qV`. Momentum `p = √(2mKE) = √(2mqV)`.
    • Momentum Ratio (e.g., Electron vs. Alpha): For equal `V`, `pe/pα = √(me qe / (mα qα))`. Given `qα = 2qe`, `pe/ pα = √(me / (2mα))`.
  • Cyclotron:
    • Inventors: E.O. Lawrence and M.S. Livingston (1930s).
    • Particles: Protons, deuterons, alpha particles (heavy ions). Not suitable for electrons due to early relativistic effects.
    • Principle: Constant magnetic field (bends path), constant frequency alternating electric field (accelerates across 'dees').
    • Path: Spiral outwards.
    • Frequency: Cyclotron frequency `f = qB / (2πm)` is constant (fixed RF).
    • Energy Limit: Relativistic mass increase (`m = γm₀`) causes particle frequency to deviate from fixed RF, leading to loss of resonance.
  • Synchrocyclotron (Frequency-Modulated Cyclotron):
    • Purpose: Overcomes the relativistic limit of the standard cyclotron for heavier particles.
    • Principle: Constant magnetic field, but the frequency of the accelerating electric field is decreased (modulated) as particle energy/mass increases to maintain resonance.
    • Output: Pulsed beam.
    • Achieves higher energies than cyclotrons for ions.
  • Betatron:
    • Inventor: Donald Kerst (1940s).
    • Particles: Primarily electrons.
    • Principle: Varying magnetic field induces an electric field (Faraday's Law of Induction) that accelerates electrons, while the magnetic field also guides them. "Magnetic induction accelerator."
    • Path: Circular, constant radius.
    • Applications: High-energy X-ray production, electron beam therapy.
  • Synchrotron:
    • Purpose: Achieves the highest particle energies.
    • Principle: Both the magnetic field (to bend path) and the frequency of the accelerating electric field are varied (synchronized) in time to keep particles on a constant radius circular path as they gain energy.
    • Magnetic Field: Increases with particle momentum to maintain constant orbital radius.
    • RF Frequency: Increases to match increasing orbital frequency.
    • Particles: Protons, electrons, heavy ions.
    • Structure: Large ring, particles injected from pre-accelerators.
    • Example: Large Hadron Collider (LHC) near Geneva, Switzerland (world's largest particle collider, operated by CERN).
  • Linear Accelerators (Linacs):
    • Principle: Particles are accelerated in a straight line through a series of drift tubes by rapidly alternating electric fields in the gaps between tubes.
    • Path: Straight. No bending magnets.
    • Particles: Electrons (high-energy), protons, ions.
    • Applications: Medical radiation therapy, injectors for circular accelerators (e.g., synchrotrons).

Quark model, Standard Model (brief overview).

  • Quark Model: Describes hadrons (protons, neutrons) as composite particles made of elementary particles called quarks.
  • Six "flavors" of quarks: up (u), down (d), charm (c), strange (s), top (t), bottom (b), each with fractional electric charge.
  • Protons are made of two up quarks and one down quark (uud); neutrons are made of one up quark and two down quarks (udd).
  • Quarks are fundamental fermions, interacting via the strong nuclear force (mediated by gluons).
  • Standard Model: A theoretical framework describing the fundamental particles and three of the four fundamental forces (strong, weak, electromagnetic) in the universe. It does not include gravity.
  • Fundamental Particles in Standard Model:
    • Fermions (matter particles):
      • Quarks: (u, d, c, s, t, b) experience the strong force.
      • Leptons: (electron, muon, tau, and their corresponding neutrinos) do not experience the strong force.
    • Bosons (force-carrying particles):
      • Photon: mediates electromagnetic force.
      • Gluon: mediates strong nuclear force.
      • W and Z bosons: mediate weak nuclear force.
      • Higgs boson: responsible for giving mass to other fundamental particles.
  • Higgs Boson ("God Particle"):
    • Predicted in 1964 by Peter Higgs and others.
    • Experimentally confirmed in 2012 by the ATLAS and CMS collaborations at CERN's Large Hadron Collider (LHC).
    • Peter Higgs and François Englert were awarded the Nobel Prize in Physics in 2013 for the theoretical prediction of the Higgs boson.
    • Its existence explains why fundamental particles have mass, by interacting with the pervasive Higgs field.

Radiation detectors: Geiger-Muller counter, Scintillation counter, Semiconductor detectors (Si(Li), Ge(Li)).

  • Radiation Detectors: Devices designed to detect and measure ionizing radiation (e.g., alpha, beta, gamma rays, X-rays).
  • Geiger-Muller (GM) Counter:
    • Principle: Gas ionization in a high electric field, leading to an "avalanche" of electrons and ions.
    • Detection: Detects alpha, beta, and gamma radiation.
    • Output: Produces a large, uniform electrical pulse and often an audible "click."
    • Characteristics: High sensitivity, simple, robust, inexpensive. No energy discrimination (pulse size independent of incident particle energy). Relatively long "dead time."
  • Scintillation Counter:
    • Principle: Ionizing radiation excites a scintillator material (e.g., NaI(Tl), plastic), which emits light photons. These photons are then converted into an electrical signal by a Photomultiplier Tube (PMT).
    • Detection: Detects alpha, beta, gamma rays, and X-rays. Excellent for gamma spectroscopy.
    • Output: Electrical pulse amplitude is proportional to the energy deposited by the incident radiation.
    • Characteristics: Good energy resolution (ability to differentiate energies), high detection efficiency for gamma rays, fast response.
  • Semiconductor Detectors:
    • Principle: Ionizing radiation creates electron-hole pairs in a reverse-biased p-n junction. The collected charge is proportional to the energy deposited.
    • Detection: Primarily X-rays, gamma rays, and charged particles.
    • Characteristics: Offer excellent energy resolution (superior to scintillation detectors), compact size.
    • Si(Li) (Silicon Lithium-drifted) Detector:
      • Material: Lithium-drifted silicon, creating a thick intrinsic region.
      • Primary Use: X-ray spectroscopy (low-energy gamma rays).
      • Requirement: Requires cryogenic cooling (e.g., liquid nitrogen) during operation to maintain lithium distribution and reduce electronic noise.
    • Ge(Li) (Germanium Lithium-drifted) Detector:
      • Material: Lithium-drifted germanium.
      • Primary Use: Gamma-ray spectroscopy (higher-energy gamma rays).
      • Requirement: Must be kept at cryogenic temperatures (e.g., liquid nitrogen) continuously (during storage and operation) to prevent lithium diffusion and reduce thermal noise.
    • HPGe (High-Purity Germanium) Detector:
      • Material: Extremely pure germanium, eliminating the need for lithium drifting.
      • Primary Use: Replaced Ge(Li) as the standard for high-resolution gamma-ray spectroscopy.
      • Requirement: Requires cooling (liquid nitrogen or electric cooler) only during operation for optimal energy resolution but can be stored at room temperature.

Radioactivity: Alpha, Beta (Fermi theory, selection rules, parity violation), Gamma decay (multipole transitions, internal conversion).

  • Radioactivity is a nuclear property involving the spontaneous disintegration of unstable atomic nuclei, emitting particles or electromagnetic radiation.
  • Alpha ($\alpha$) Decay:
    • Emits an alpha particle ($^42$He nucleus, 2 protons, 2 neutrons), which is positively charged (+2e).
    • Mass number (A) decreases by 4; Atomic number (Z) decreases by 2.
    • Example: ${92}$U$^{238}$ $\rightarrow$ ${90}$Th$^{234}$ + $^42$He.
    • High ionizing power, low penetration power.
  • Beta ($\beta$) Decay:
    • Emits an electron ($\beta^-$) or a positron ($\beta^+$).
    • Mass number (A) remains unchanged. Atomic number (Z) changes by $\pm 1$.
    • Beta rays are particles, not electromagnetic radiation.
    • Moderate ionizing power, moderate penetration power.
    • $\beta^-$ Decay: Neutron converts to proton (n $\rightarrow$ p + e$^-$ + $ \bar{\nu}e$). Z increases by 1. Example: $^{14}6$C $\rightarrow$ $^{14}7$N + e$^-$ + $\bar{\nu}e$.
    • $\beta^+$ Decay: Proton converts to neutron (p $\rightarrow$ n + e$^+$ + $\nue$). Z decreases by 1.
    • Electron Capture (EC): Nucleus captures an inner atomic electron (p + e$^-$ $\rightarrow$ n + $\nue$). Z decreases by 1.
    • Fermi Theory of Beta Decay: Explains the continuous energy spectrum of emitted electrons/positrons by postulating the simultaneous emission of a neutrino/antineutrino, sharing the decay energy.
    • Selection Rules: Govern allowed/forbidden transitions based on changes in nuclear angular momentum ($\Delta J$) and parity ($\Delta \pi$). Allowed transitions generally involve small $ \Delta J$ and no parity change ($ \Delta \pi = \text{No}$).
    • Parity Violation: Observed in weak interactions (including beta decay), where the mirror image of a decay process is not identical to the real process, meaning parity is not conserved.
  • Gamma ($\gamma$) Decay:
    • Emits a high-energy photon (gamma ray) from an excited nucleus.
    • Neither mass number (A) nor atomic number (Z) changes. The nucleus transitions from a higher energy state to a lower energy state.
    • Gamma rays are electromagnetic radiation.
    • Lowest ionizing power, highest penetration power.
    • Often follows alpha or beta decay if the daughter nucleus is in an excited state.
    • Multipole Transitions: Gamma transitions are classified by the angular momentum (L) and parity change carried by the photon (Electric EL or Magnetic ML). Selection rules dictate allowed transitions based on initial/ final nuclear spins and parities.
    • Internal Conversion (IC): An alternative to gamma emission where the excited nucleus transfers its energy directly to an atomic electron, ejecting it. No change in A or Z.
  • Radioactive Disintegration Series: Uranium (U-238) ultimately disintegrates into stable Lead (Pb-206).
  • Half-life ($T{1/2}$): Time required for half of the radioactive nuclei in a sample to decay. Amount remaining $N = N0 (1/2)^{t/T{1/2}} $.
  • Average Life ($\tau$): $\tau = T{1/2} / \ln 2 \approx 1.44 T{1/2}$. In one average life, approximately 63.2% of the substance decays.
  • Applications of Radioisotopes:
    • Cobalt-60 (Co-60): Used in radiotherapy for cancer treatment (emits gamma rays).
    • Iodine-131 (I-131): Used for thyroid treatment.
    • Carbon-14 (C-14):
      • Produced in the atmosphere by cosmic ray neutrons colliding with nitrogen nuclei ($^{14}$N + n $\rightarrow$ $^{14}$C + p).
      • Decays by $\beta^-$ emission.
      • Used in radiocarbon dating for estimating the age of ancient organic materials (fossils).
    • Uranium dating: Used to estimate the age of the Earth and rocks.
    • Beta radiations: Used to control the thickness of thin materials like paper and plastic sheets during production.
    • Gamma radiations: Used in radiotherapy and for controlling the thickness of denser materials like metal sheets.
  • Alpha and Beta rays are particles (not electromagnetic waves); X-rays and Gamma rays are electromagnetic waves.

13. Computer and Information

Technology

Practice MCQs: Nuclear Physics

Basic properties of nuclei: size, shape, charge, mass, spin, magnetic dipole and electric quadrupole moments.

  1. Which of the following elements does not contain neutrons?

    Asked in: BPSC Prelims Exam 64th

    1. Oxygen
    2. Nitrogen
    3. Hydrogen
    4. Copper
    Show answer

    Answer: C. Hydrogen

    - Atoms are made of protons, neutrons, and electrons. - Protons define the element (atomic number). - Neutrons are found in the nucleus alongside protons. - Isotopes of an element have the same number of protons but different numbers of neutrons. - Hydrogen (specifically the isotope Protium, $^1$H) has 1 proton and 0 neutrons.

  2. The number of neutrons in the nucleus of plutonium $(_{94}Pu^{242})$ is

    Asked in: BPSC Prelims Exam 66th

    1. 94
    2. 148
    3. 242
    4. 336
    Show answer

    Answer: B. 148

    The atomic number identifies the element, and the mass number identifies the specific isotope.

  3. The mass number of a nucleus is

    Asked in: BPSC Prelims Exam 67th Cancelled

    1. the sum of the numbers of neutrons and protons
    2. the total mass of neutrons and protons
    3. always more than the atomic weight
    4. always less than its atomic number
    Show answer

    Answer: A. the sum of the numbers of neutrons and protons

    The mass number (A) of an atomic nucleus is defined as the total number of nucleons within the nucleus. Nucleons are protons and neutrons. Therefore, Mass Number (A) = Number of Protons (Z) + Number of Neutrons (N).

  4. The nucleus of an atom consists of

    Asked in: BPSC Prelims Exam 67th Re Exam

    1. electrons and protons
    2. protons and neutrons
    3. electrons only
    4. electrons and neutrons
    Show answer

    Answer: B. protons and neutrons

    The atomic nucleus is composed of nucleons, which are protons and neutrons. Electrons are located outside the nucleus.

  5. Who proposed the 'Plum Pudding Model' for an atom?

    Asked in: UPSC CDS 1 2017

    1. Antoine Lavoisier
    2. Robert Boyle
    3. Ernest Rutherford
    4. J.J. Thomson
    Show answer

    Answer: D. J.J. Thomson

    The Plum Pudding Model suggested that the atom was a sphere of positive charge with negatively charged electrons embedded within it, much like plums in a pudding.

  6. Scattering of α-particles by a thin gold foil suggests the presence of

    Asked in: UPSC CDS 1 2020

    1. electron in an atom
    2. proton in an atom
    3. positively charged nucleus at the centre of an atom
    4. isotopes of gold
    Show answer

    Answer: C. positively charged nucleus at the centre of an atom

    The deflection of positively charged alpha particles at large angles, and the reflection of a few back towards the source, indicated that they were encountering a strong positive charge concentrated in a very small volume within the atom, which was termed the nucleus.

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

    Asked in: UPSC CDS 2 2019

    1. electron
    2. proton
    3. atomic nucleus
    4. neutron
    Show answer

    Answer: C. 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.

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

    Asked in: UPSC CDS 2 2020

    1. Neutron mass is almost equal to proton mass.
    2. Neutrons possess zero charge.
    3. Neutrons are located inside the atomic nuc‐ lei.
    4. Neutrons revolve around the atomic nuclei.
    Show answer

    Answer: D. Neutrons revolve around the atomic nuclei.

    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.

Binding energy, mass defect, packing fraction, semi-empirical mass formula (Weizsäcker formula) and its applications.

  1. Nucleus ²⁴⁰U, which has a binding energy per nucleon as 7·6 MeV, disintegrates into two nuclei of ¹¹⁹⋅⁵Sn. Take ¹¹⁹⋅⁵Sn elements atomic mass number as 120 and binding energy per nucleon as 8·4 MeV. Which one among the following is the correct value of the energy released in the disintegration process ?

    Asked in: UPSC Geoscientist 2024

    1. 192 MeV
    2. 190 MeV
    3. 188 MeV
    4. 3840 MeV
    Show answer

    Answer: A. 192 MeV

    - The initial nucleus is ²⁴⁰U with A=240 and binding energy per nucleon = 7.6 MeV. Total binding energy of ²⁴⁰U = 240 7.6 MeV. - The nucleus disintegrates into two nuclei of ¹¹⁹⋅⁵Sn. We are given to use the atomic mass number as 120 for calculation. So, the two product nuclei have A=120 and binding energy per nucleon = 8.4 MeV. - Total binding energy of the two product nuclei = 2 (120 8.4 MeV). - The energy released in a nuclear reaction is the difference between the total binding energy of the products and the total binding energy of the reactants. Energy released = (Total binding energy of products) - (Total binding energy of reactants). - Energy released = 240 0.8 MeV - Energy released = 192 MeV.

  2. Homi Brmbha award is given for special contribution in the field of

    Asked in: UPPCS Prelims 2012

    1. Theoretical Physics
    2. Nuclear Energy
    3. Laser Physics
    4. Space Research
    Show answer

    Answer: B. Nuclear Energy

    Homi J. Bhabha was an Indian nuclear physicist who is considered the "father of India's nuclear programme". He founded the Tata Institute of Fundamental Research (TIFR) and the Atomic Energy Establishment, Trombay (AEET), which was later renamed the Bhabha Atomic Research Centre (BARC) in his honor.

  3. Consider the following statements: Statement-I (Assertion A) -Earnest Rutherford asserted before the Royal Society that man will never get nuclear power Statement-II (Reason R) - He was sure that Einstein law will fail, and mass wil not be converted into energy. Select your answer from the coding scheme given BELOW

    Asked in: UPPCS Prelims 1994

    1. Both (A) and (R) are true and (R) is correct explanation of (A).
    2. Both (A) and (R) are true but (R) is correct explanation of (A).
    3. (A) is true and (R) is false.
    4. (A) is false but (R) is true.
    Show answer

    Answer: C. (A) is true and (R) is false.

    Statement I (Assertion A) is considered broadly true. While the exact quote and context are debated, Ernest Rutherford was highly skeptical about the practical possibility of harnessing nuclear energy on a significant scale for power generation based on the knowledge and technology available in the early 20th century. He made statements suggesting it was highly unlikely. Statement II (Reason R) is false. Rutherford's skepticism was not due to doubting Einstein's law E=mc² or the principle of mass-energy conversion. Einstein's formula provided the theoretical basis for the immense energy released in nuclear reactions, which Rutherford's experiments were exploring. Rutherford's doubts were more related to the technical feasibility of creating and controlling a sustained, energy-producing nuclear reaction. Therefore, while Assertion A is true, Reason R is false and does not explain A.

  4. Which of the following is a wrong description of binding energy of a nucleus?

    Asked in: WBCS Main Paper 4 2021

    1. It is the energy required to break a nucleus into its constituent nucleons.
    2. It is the energy made available when free nucleons combine to form a nucleus.
    3. It is the sum of the rest mass energies of its nucleons minus the rest mass of the nucleus.
    4. It is the sum of the kinetic energy of all the nucleons in the nucleus.
    Show answer

    Answer: D. It is the sum of the kinetic energy of all the nucleons in the nucleus.

    Nuclear binding energy is related to the mass defect (difference between the mass of constituent nucleons and the nucleus) and the energy required to overcome the strong force binding them, not solely the sum of their kinetic energies.

  5. Who was the first Chairman of the Atomic Energy Commission ? (1) Jawaharlal Lal Nehru (2) Krishna Menon (3) Homi J. Bhabha (4) Shanti Swaroop Bhatnagar

    Asked in: Protection Officer 2022

    1. Option text
    2. Option text
    3. Option text
    4. Option text
    Show answer

    Answer: C. Option text

    Homi J. Bhabha was the first Chairman of the Atomic Energy Commission of India.

  6. As per Einsteins theory, energy equivalent of 1 gm (One gram) substance will be : - (a) $5.6 \times 10^{26}$ Mev - (b) $9.09 \times 10^{32}$ \times 10^{32}$ Mev

    Asked in: Assistant Engineer (AE) Exam 2013

    1. $5.6 \times 10^{26}$ Mev
    2. $9.09 \times 10^{32}$ Mev
    3. $5.6 \times 10^{29}$ Mev
    4. $5.6 \times 10^{32}$ Mev
    Show answer

    Answer: A. $5.6 \times 10^{26}$ Mev

    The calculation requires using Einstein's mass- energy equivalence formula ($E=mc^2$) and performing unit conversions from grams to kilograms, and from Joules to Mega-electron Volts.

  7. As per Einsteins theory, energy equivalent of 1 gm (One gram) substance will be :

    Asked in: Assistant Engineer (AE) Exam 2013

    1. 5.6 x 10²⁶ Mev
    2. 9.09 x 10²³ Mev
    3. 5.6 x 10²⁹ Mev
    4. 5.6 x 10³² Mev
    Show answer

    Answer: A. 5.6 x 10²⁶ Mev

    Einstein's theory of special relativity states that mass and energy are interchangeable. The formula E=mc² quantifies this relationship, where E is energy, m is mass, and c is the speed of light. To calculate the energy, we need to convert grams to kilograms and then use the value of c, and finally convert Joules to MeV.

Conservation laws in particle physics (baryon number, lepton number, strangeness, isospin, parity).

  1. The photoelectric effect is based on the law of conservation of

    Asked in: ae 2024

    1. Angular momentum
    2. Mass
    3. Energy
    4. Momentum
    Show answer

    Answer: C. Energy

    The photoelectric effect, explained by Albert Einstein, demonstrates that light energy is quantized into packets called photons. When a photon strikes a metal surface, its energy is transferred to an electron. If this energy is sufficient, the electron is ejected. This process strictly adheres to the principle of conservation of energy, where the energy of the incident photon equals the sum of the work function of the metal and the kinetic energy of the ejected electron.

Elementary particles: classification (leptons, hadrons, quarks), fundamental interactions (strong, weak, electromagnetic, gravitational).

  1. 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.

    Asked in: UPSC CDS 1 2024

    1. 1 and 4 only
    2. 1, 2, 3 and 4
    3. 2 and 3 only
    4. 1, 2 and 3 only
    Show answer

    Answer: B. 1, 2, 3 and 4

    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.

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

    Asked in: UPSC CDS 1 2024

    1. 0.5 MeV
    2. 900 MeV
    3. 100 GeV
    4. 1000 GeV
    Show answer

    Answer: C. 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.

  3. Which country is building the world's largest neutrino-detecting telescope, “Trident”?

    Asked in: GPSC Prelims CSP 2 2024

    1. China
    2. Japan
    3. United States
    4. Russia
    Show answer

    Answer: A. China

    China is currently constructing the Tropical Deep-sea Neutrino Telescope (TRIDENT), which is planned to be the world's largest neutrino- detecting telescope.

  4. Which of the following are the properties of an electron? 1. Electron is a constituent of cathode ray 2. Electron is a negatively charged particle 3. The mass of the electron is equal to the mass of the proton 4. Electron is deflected by the electric field but not by magnetic field Select the correct answer using the code given below:

    Asked in: UPSC NDA 2 2015

    1. 1 and 2 only
    2. 1, 2 and 3
    3. 3 and 4
    4. 1 and 4
    Show answer

    Answer: A. 1 and 2 only

    This question tests basic properties of electrons, a fundamental particle in physics and chemistry.

  5. In the recent past, a fundamental particle has been claimed to be experimentally observed, at a European Laboratory in Geneva, to travel at a speed greater than that of light in vacuum. The name of the particle is

    Asked in: UPSC CAPF 2012

    1. electron
    2. positron
    3. neutron
    4. neutrino
    Show answer

    Answer: D. neutrino

    The particle involved in the experiment claiming superluminal speed was the neutrino. The results were later attributed to experimental errors, specifically a faulty cable connection in the GPS timing system and an oscillator issue, and the initial claim was retracted.

  6. Consider the following statements: 1. Discovery of Higgs boson of which scientists are almost certain, may discard Einstein's special theory of relativity. 2. Probable discovery of a particle which moves faster than light may prove Stephen Hawking wrong. 3. Probable discovery of a particle that moves faster than light may go against Einstein's special theory of relativity. Which of the statements given above is/are correct?

    Asked in: UPSC CAPF 2012

    1. 1 and 2
    2. 1 only
    3. 3 only
    4. 1 and 3
    Show answer

    Answer: C. 3 only

    Special relativity sets the speed of light as the ultimate speed limit in the universe. Any particle exceeding this speed would violate its principles, particularly causality.

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

    Asked in: UPSC CAPF 2015

    1. Bodi hills in Tamil Nadu
    2. Kaina hills in Manipur
    3. Jampui hills in Tripura
    4. Nallamala hills in Andhra Pradesh
    Show answer

    Answer: A. 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.

  8. 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?

    Asked in: UPSC IAS 2013

    1. Gravity is the strongest of the four
    2. Electromagnetism acts only on particles with an electric charge
    3. Weak nuclear force causes radioactivity
    4. Strong nuclear force holds protons and neutrons inside the nucleus of an atom
    Show answer

    Answer: A. Gravity is the strongest of the four

    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.

Nature of nuclear force: characteristics, deuteron problem, meson theory (Yukawa potential).

  1. Nuclear forces are

    Asked in: TNPSC CS Prelims 2019

    1. strongly attractive force
    2. strongly repulsive force
    3. attractive or repulsive depend on nucleons
    4. gravitational forces
    Show answer

    Answer: C. attractive or repulsive depend on nucleons

    - Nuclear forces are strongly attractive at typical inter-nucleon distances within the nucleus (around 0.8 fm to a few fm). - However, they become strongly repulsive at very short distances (less than about 0.8 fm), preventing the collapse of the nucleus. - They are the strongest fundamental forces in nature over their very short range. - They are largely charge-independent, acting equally between proton-proton, neutron-neutron, and proton-neutron pairs. - The fact that they are both attractive and repulsive depending on the separation distance between nucleons is a key characteristic.

Nuclear fission: theory, chain reaction, critical mass, nuclear reactors (types, components, safety aspects).

  1. Which of the following statements about 'fission' is correct ? 1. It is related with the creation of new individuals by means of cell division in unicellular organism. 2. It is related with the transformation of heavier nuclei into smaller nuclei. 3. It is related with the creation of a heavier nuclei by means of combining two higher nuclei. Select the correct answer using the code given below :

    Asked in: UPSC CDS 1 2021

    1. 1 only
    2. 2 only
    3. 1 and 2 only
    4. 1 and 3 only
    Show answer

    Answer: C. 1 and 2 only

    Fission refers to splitting or division, occurring in both biological (cell division) and nuclear (heavy nucleus splitting) contexts. Fusion is the combining of nuclei.

  2. 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?

    Asked in: UPSC CDS 2 2017

    1. 1 and 3
    2. 2 and 3
    3. 4 only
    4. 1 and 4
    Show answer

    Answer: B. 2 and 3

    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.

  3. Which is not used as Atomic fuel ?

    Asked in: CGPSC Prelims Exam 2014

    1. Uranium
    2. Thorium
    3. Plutonium
    4. Lead
    Show answer

    Answer: D. Lead

    Atomic fuel, also known as nuclear fuel, is material used in nuclear reactors to sustain a nuclear chain reaction for energy production. The most common atomic fuels are fissile isotopes like Uranium-235 and Plutonium-239. Thorium-232 is a fertile material that can be converted into fissile Uranium-233, making it a potential nuclear fuel source. Uranium, Thorium, and Plutonium are all associated with nuclear energy production as fuel or potential fuel. Lead is a heavy metal and is not fissile or fertile in the context of nuclear reactors; it is sometimes used for radiation shielding or as a coolant in certain reactor designs, but not as fuel itself.

  4. Which one of the following statements is true for nuclear fission processes?

    Asked in: UPSC Geoscientist 2022

    1. Light initial nuclides have lesser number of neutrons than protons.
    2. Heavy initial nuclides have lesser number of neutrons than protons.
    3. All initial nuclides have larger number of neutrons than protons.
    4. All initial nuclides have equal number of protons and neutrons.
    Show answer

    Answer: C. All initial nuclides have larger number of neutrons than protons.

    - Fission involves heavy nuclei. - Heavy stable and fissionable nuclei have N > Z. - The neutron-to- proton ratio increases with increasing atomic number for stable nuclei.

  5. What is the use of heavy water?

    Asked in: UPSC Geoscientist 2023

    1. It is used in nuclear reactors as a moderator
    2. It is used in nuclear reactors as fuel
    3. It is used in radiation therapy for cancer
    4. It is used in water softening plants
    Show answer

    Answer: A. It is used in nuclear reactors as a moderator

    Heavy water acts as a neutron moderator in certain types of nuclear reactors, effectively slowing down neutrons without absorbing them significantly.

  6. Which of the following statements is/are correct? 1. In the reactor core, when uranium-235 is hit by a fast moving neutron, it breaks into lighter elements. 2. The process of chain reaction in a reactor depends on the presence of a moderator such as Petrol and Diesel 3. Thousands of small pellets of ceramic uranium oxide fuel make up the core of a reactor.

    Asked in: GPSC Prelims CSP 2 2019

    1. 1 and 3 only
    2. 2 and 3 only
    3. 1, 2 and 3
    4. 1 and 2 only
    Show answer

    Answer: A. 1 and 3 only

    Nuclear reactors use controlled nuclear fission to generate heat. The key components are fuel (e.g., U-235), moderator (to slow neutrons, usually water or graphite), control rods (to absorb neutrons and regulate reaction), and coolant (to transfer heat).

  7. Which of the following pairs are correctly matched? Kudankulam - Water Energetic Reactor Kaiga - Pressurized Heavy Water Reactor Tarapur - Boiling water reactor and Pressurized heavy water reactor

    Asked in: GPSC Prelims CSP 2 2021

    1. 1, 2 and 3
    2. 2 and 3 only
    3. 1 and 3 only
    4. 1 and 2 only
    Show answer

    Answer: A. 1, 2 and 3

    Kudankulam Nuclear Power Plant uses VVER (Water-Water Energetic Reactor) reactors, which are a type of light water reactor. Kaiga Generating Station uses Pressurized Heavy Water Reactors (PHWRs). Tarapur Atomic Power Station houses both Boiling Water Reactors (BWRs) (Units 1 & 2) and Pressurized Heavy Water Reactors (PHWRs) (Units 3 & 4).

  8. Which one of the following minerals is used as a fuel in nuclear power stations ?

    Asked in: UPSC NDA 1 2019

    1. Bauxite
    2. Quartz
    3. Feldspar
    4. Pitchblende
    Show answer

    Answer: D. Pitchblende

    Nuclear power stations use fissile materials, primarily uranium, as fuel for nuclear fission. Pitchblende is a mineral that is a major ore of uranium. Bauxite is the main ore of aluminium. Quartz is a common mineral made of silicon dioxide. Feldspar is a group of rock-forming silicate minerals. Therefore, Pitchblende is the mineral associated with the fuel used in nuclear power stations.

Nuclear fusion: stellar energy processes, controlled thermonuclear fusion.

  1. Hydrogen bomb is based on the principle of

    Asked in: BPSC Prelims Exam 67th Cancelled UPPCS Prelims 2010

    1. controlled fusion reaction
    2. uncontrolled fusion reaction
    3. controlled fission reaction
    4. uncontrolled fission reaction
    Show answer

    Answer: B. uncontrolled fusion reaction

    A hydrogen bomb (thermonuclear weapon) utilizes the nuclear fusion of light atomic nuclei, such as isotopes of hydrogen (deuterium and tritium), into heavier nuclei, releasing vast amounts of energy. This process requires extremely high temperatures and pressures, usually initiated by a fission reaction (an atomic bomb). The fusion reaction in a hydrogen bomb is uncontrolled, leading to an explosive release of energy.

  2. The hydrogen bomb and the uranium bomb are based, respectively on

    Asked in: UPSC CDS 1 2023

    1. nuclear fusion and fission
    2. fission and thermonuclear fusion
    3. geothermal fission and fusion
    4. geothermal fusion and fission
    Show answer

    Answer: A. nuclear fusion and fission

    - Hydrogen bomb uses nuclear fusion. - Uranium bomb uses nuclear fission. - Both processes release enormous amounts of energy, but fusion generally releases more energy per unit mass than fission.

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

    Asked in: UPSC Geoscientist 2021

    1. Nuclear fission
    2. Nuclear fusion
    3. Atomic collision
    4. Atomic excitation
    Show answer

    Answer: B. Nuclear fusion

    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.

  4. Assertion (A) : Uranium can undergo a nuclear fusion reaction. Reason (R) : Uranium has a big unstable nucleus.

    Asked in: GPSC Prelims CSP 1 2022

    1. Both A and R are true and R is the correct explanation of A.
    2. Both A and R are true but R is not the correct explanation of A.
    3. A is true, R is false
    4. A is false, R is true
    Show answer

    Answer: D. A is false, R is true

    - Nuclear fusion involves combining light nuclei. - Nuclear fission involves splitting heavy nuclei. - Uranium is a heavy element known for nuclear fission. - Uranium's nucleus is indeed large and relatively unstable, which facilitates fission.

  5. Consider the following statements: 1. In nuclear fusion, energy is released when atoms are combined or fused together to form a larger atom. This is how the sun produces energy. 2. In nuclear fission, atoms are split apart to form smaller atoms, releasing energy. Nuclear power plants use nuclear fission to produce electricity. Evaluate the statements

    Asked in: GPSC Prelims CSP 2 2023

    1. Only 1 is correct
    2. Only 2 is correct
    3. Both 1 and 2 are correct
    4. Both 1 and 2 are not correct
    Show answer

    Answer: C. Both 1 and 2 are correct

    Nuclear fusion involves combining light atomic nuclei to form a heavier nucleus, releasing vast amounts of energy, as seen in stars like the Sun. Nuclear fission involves splitting heavy atomic nuclei into lighter nuclei, also releasing energy, which is the process used in nuclear power plants.

  6. Which statement is not associated with nuclear fission ?

    Asked in: UKPSC CS Prelims 2016

    1. Neutron-induced nuclear reaction.
    2. Energy generation in stars.
    3. Source of energy in nuclear reactor that produces electricity.
    4. Enormous energy is released in an atom bomb.
    Show answer

    Answer: B. Energy generation in stars.

    - Nuclear fission is the splitting of an atomic nucleus. - It is used in nuclear reactors and atom bombs. - Stars generate energy through nuclear fusion, not fission.

  7. Most of the sources of energy we use, represent stored solar energy. Which of the following is NOT ultimately derived form the sun's energy?

    Asked in: UPPCS Prelims 2022

    1. Biomass energy
    2. Nuclear energy
    3. Wind energy
    4. Geothermal energy
    Show answer

    Answer: D. Geothermal energy

    Energy sources can be broadly classified based on their origin. Solar-derived sources include solar, wind, hydro, biomass. Non-solar derived sources include nuclear, geothermal, and tidal.

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

    Asked in: UPSC CISF AC EXE 2023

    1. Nuclear fission
    2. Nuclear fusion
    3. Chemical reaction
    4. Photochemical reaction
    Show answer

    Answer: B. Nuclear fusion

    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 reactions: conservation laws, Q-value, cross-section, compound nucleus and direct reactions.

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

    Asked in: UPSC CDS 2 2016

    1. 10 MeV
    2. 100 MeV
    3. 1 MeV
    4. 0·1 MeV
    Show answer

    Answer: A. 10 MeV

    The energy (E) and momentum (p) of a photon are related by the formula E = pc.

Particle accelerators: Cyclotron, Synchrocyclotron, Betatron, Synchrotron, Linear accelerators.

  1. The branch of physics that deals with the motion of a very small particles is called:

    Asked in: RPSC RAS Prelims 2003

    1. Field theory
    2. Particle physics
    3. Quantum mechanics
    4. Atomic physics
    Show answer

    Answer: C. Quantum mechanics

    Quantum mechanics is the branch of physics that studies the behavior of matter and energy at the smallest scales, specifically dealing with the motion and interaction of subatomic particles (like electrons, protons, neutrons) and atoms. At these scales, the classical laws of physics often break down, and quantum effects become significant.

  2. The ratio of momenta of an electron and an $\alpha$-particle which are accelerated from the rest by a potential difference of 100 volt is ($m_e$ - mass of electron, $m_\alpha$ - mass of $\alpha$-particle)

    Asked in: Co operative Supervisor & Environment Supervisor (Group C) Exam 2023

    1. 1
    2. $\sqrt{\frac{2m_e}{m_\alpha}}$
    3. $\sqrt{\frac{m_e}{m_\alpha}}$
    4. $\sqrt{\frac{m_e}{2m_\alpha}}$
    Show answer

    Answer: B. $\sqrt{\frac{2m_e}{m_\alpha}}$

    The momentum of a charged particle accelerated from rest by a potential difference $V$ is given by $p = \sqrt{2mqV}$, where $m$ is the mass, $q$ is the charge, and $V$ is the potential difference. The charge of an electron is $e$. The charge of an $ \alpha$-particle is $2e$. The mass of an electron is $m_e$. The mass of an $\alpha$-particle is $m_\alpha$. The potential difference is the same for both (100 volt).

  3. The world's largest particle collider near Geneva is named

    Asked in: FINANCE AND ACCOUNTS OFFICER TREASURY OFFICER 2016

    1. Liquid Nitrogen Collider
    2. Liquid Accelerator Collider
    3. Large Hadron Collider
    4. Large Accelerator Collider
    Show answer

    Answer: C. Large Hadron Collider

    This question pertains to major scientific facilities and their names.

Quark model, Standard Model (brief overview).

  1. Large Hadron Collider was in news recently for doing some scientific research to prove the presence of an elementary particle. The scientist who predicted this particle in 1964 has been awarded Nobel Prize in 2013. What is this discovery ?

    Asked in: UPSC CAPF 2014

    1. Particles known as quarks having mass
    2. Origin of Universe timings
    3. Bigg's Bosons or God Particles explaining why fundamental particles have mass
    4. None of the above
    Show answer

    Answer: C. Bigg's Bosons or God Particles explaining why fundamental particles have mass

    The Higgs boson is an elementary particle associated with the Higgs field. This field is thought to be present throughout the universe, and interactions with it give other fundamental particles (like quarks and leptons) their mass. It is often popularly referred to as the "God particle".

Radiation detectors: Geiger-Muller counter, Scintillation counter, Semiconductor detectors (Si(Li), Ge(Li)).

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

    Asked in: UPSC Geoscientist 2022

    1. CT scans and X-rays only
    2. MRI scans and X-rays only
    3. CT scans, MRI scans and Ultrasonography only
    4. CT scans, MRI scans, Ultrasonography and X- rays
    Show answer

    Answer: A. CT scans and X-rays only

    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.

Radioactivity: Alpha, Beta (Fermi theory, selection rules, parity violation), Gamma decay (multipole transitions, internal conversion).

  1. Which among the following is a positively charged particle emitted by a radioactive element?

    Asked in: BPSC Prelims Exam 68th

    1. Beta ray
    2. Alpha ray
    3. Cathode ray
    4. More than one of the above
    Show answer

    Answer: B. Alpha ray

    Alpha particles are composed of protons and neutrons and carry a net positive charge, making Alpha ray a positively charged radiation emitted by radioactive elements.

  2. In the gamma decay of a nucleus

    Asked in: UPSC CDS 2 2016

    1. the mass number of the nucleus changes whereas its atomic number does not change
    2. the mass number of the nucleus does not change whereas its atomic number changes
    3. both the mass number and the atomic number of the nucleus change
    4. neither the mass number nor the atomic number of the nucleus changes
    Show answer

    Answer: D. 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.

  3. The ultimate product of radioactive disintegration of uranium is

    Asked in: CGPSC Prelims Exam 2013

    1. Lead
    2. Radium
    3. Thorium
    4. Plutonium
    Show answer

    Answer: A. Lead

    The decay chain of Uranium-238 ends with Lead-206, and the decay chain of Uranium-235 ends with Lead-207. Thorium and Radium are intermediate products in the decay series, not the final stable element.

  4. Which one of the following statements for the emission spectrum of hydrogen is true?

    Asked in: UPSC Geoscientist 2023

    1. The Lyman series lies in the visible region and the Paschen series lies in the infrared region.
    2. The Lyman series lies in the ultraviolet region and the Paschen series lies in the infrared region.
    3. Both the Lyman and the Paschen series lie in the visible region.
    4. The Lyman series lies in the ultraviolet region and the Paschen series lies in the visible region.
    Show answer

    Answer: B. The Lyman series lies in the ultraviolet region and the Paschen series lies in the infrared region.

    Different series in the hydrogen emission spectrum are defined by the principal quantum number of the final energy level of the electron transition. The energy and thus the region of the spectrum depend on the energy difference between the initial and final levels.

  5. When $\alpha$-particle emits from a radioactive element then (1) atomic number decreases by 2 and mass number decreases by 4 (2) atomic number decreases by 1 and mass number decreases by 2 (3) atomic number increases by 1 (4) atomic number and mass number remains same

    Asked in: MPSC CS Prelims 2023

    1. atomic number decreases by 2 and mass number decreases by 4
    2. atomic number decreases by 1 and mass number decreases by 2
    3. atomic number increases by 1
    4. atomic number and mass number remains same
    Show answer

    Answer: A. atomic number decreases by 2 and mass number decreases by 4

    Alpha decay results in a decrease of the atomic number by 2 and the mass number by 4.

  6. Which one of the following element's isotope is used in the treatment of cancer ?

    Asked in: UPSC NDA 2 2020

    1. Uranium
    2. Cobalt
    3. Sodium
    4. Iodine
    Show answer

    Answer: B. Cobalt

    - Radioisotopes like Cobalt-60 are used in cancer treatment (radiotherapy) to damage the DNA of cancer cells and prevent them from growing and dividing. - Iodine-131 is used specifically in the treatment of thyroid cancer and hyperthyroidism. - Uranium is primarily known for its use in nuclear power and weapons, not medical treatment in this context. - Sodium isotopes are often used as tracers but not standard therapeutic agents for cancer.

  7. Which of the following cause is responsible for production of Radiocarbon in the atmosphere ?

    Asked in: OPSC CS Prelims 2021

    1. Atmosphere lightning discharge in atmosphere
    2. Action of ultraviolet light from the Sun on atmospheric oxygen
    3. Action of solar radiations particularly cosmic rays on carbon dioxide present in the atmosphere
    4. Collision between fast neutrons and nitrogen nuclei present in the atmosphere
    Show answer

    Answer: D. Collision between fast neutrons and nitrogen nuclei present in the atmosphere

    High-energy cosmic rays from outer space collide with atoms in the upper atmosphere, producing secondary particles, including fast neutrons. These neutrons collide with nitrogen nuclei (¹⁴N), causing a nuclear reaction (¹⁴N + n → ¹⁴C + p) where a nitrogen nucleus absorbs a neutron and emits a proton, transforming into a Carbon-14 atom.

  8. The half-life period of a radioactive substance is 70 days. One gram of the same substance will become 0.25 gm after

    Asked in: PPSC CS Prelims 2018

    1. 140 days
    2. 70 days
    3. 210 days
    4. 280 days
    Show answer

    Answer: A. 140 days

    The half-life of a radioactive substance is the time it takes for half of the original amount of the substance to decay. - Initial amount = 1 gm. - After 1 half-life (70 days), the amount remaining is $1 \text{ gm} \times \frac{1}{2} = 0.5 \text{ gm}$. - After 2 half-lives (70 + 70 = 140 days), the amount remaining is $0.5 \text{ gm} \times \frac{1}{2} = 0.25 \text{ gm}$. So, it takes 2 half-lives for the original amount to reduce to one-quarter (0.25 gm is one-quarter of 1 gm).