Question 1
What are isotopes?
Correct Answer: Nuclei with the same atomic number (Z) but different mass numbers (A)
Question 2
What are isobars?
Correct Answer: Nuclei with the same mass number (A) but different atomic numbers (Z)
Question 3
What are isotones?
Correct Answer: Nuclei with the same number of neutrons (N = A - Z)
Question 4
The radius R of a nucleus with mass number A is proportional to:
Correct Answer: A^(1/3)
Question 5
What is the formula for nuclear radius R in terms of nuclear radius constant R₀ (≈ 1.2 fm) and mass number A?
Correct Answer: R = R₀ A^(1/3)
Question 6
How does nuclear density vary with the mass number A?
Correct Answer: It is independent of A (constant for all nuclei)
Question 7
What is the approximate order of magnitude of nuclear density?
Correct Answer: 2.3 × 10¹⁷ kg/m³
Question 8
What is mass defect (Δm) of a nucleus?
Correct Answer: Difference between total mass of individual nucleons and actual mass of the nucleus
Question 9
Einstein's mass-energy equivalence relation is given by:
Correct Answer: E = m c²
Question 10
Nuclear binding energy per nucleon is maximum for nuclei around mass number:
Correct Answer: A = 50 to 80 (Iron region, Fe-56)
Question 11
Which of the following forces is responsible for holding protons and neutrons together inside a nucleus?
Correct Answer: Nuclear force (strong interaction)
Question 12
Nuclear forces are characterized by being:
Correct Answer: Short-ranged, strongly attractive, and charge-independent
Question 13
Radioactivity was discovered by:
Correct Answer: Henri Becquerel
Question 14
What is emitted during alpha (α) decay?
Correct Answer: A helium nucleus (²⁴He)
Question 15
What is emitted during beta-minus (β⁻) decay?
Correct Answer: An electron and an antineutrino
Question 16
What is emitted during gamma (γ) decay?
Correct Answer: High-frequency electromagnetic radiation (photons)
Question 17
The radioactive law of disintegration states that the rate of decay (dN/dt) is proportional to:
Correct Answer: The number of undecayed nuclei present at that instant (N)
Question 18
What is the formula relating half-life (T_1/2) and decay constant (λ)?
Correct Answer: T_(1/2) = 0.693 / λ
Question 19
What is mean life (τ) of a radioactive sample in terms of decay constant (λ)?
Correct Answer: τ = 1 / λ
Question 20
What is nuclear fission?
Correct Answer: Splitting of a heavy nucleus into two or more smaller fragments with release of energy
Question 21
What is nuclear fusion?
Correct Answer: Combining of two light nuclei to form a heavier nucleus, releasing energy
Question 22
What is the SI unit of radioactivity activity?
Correct Answer: Becquerel (Bq) or Curie (Ci)
Question 23
1 Curie (Ci) is equal to how many disintegrations per second (Bq)?
Correct Answer: 3.7 × 10¹⁰ disintegrations/second
Question 24
Which of the following particles is used to induce fission in Uranium-235 in nuclear reactors?
Correct Answer: Thermal neutron
Question 25
What is the function of heavy water (D₂O) or graphite in a nuclear reactor?
Correct Answer: Moderator (to slow down fast neutrons)
Question 26
What is the function of control rods (like cadmium or boron) in a nuclear reactor?
Correct Answer: To absorb excess neutrons and control the chain reaction rate
Question 27
What is the binding energy per nucleon for the most stable nuclei like iron (Fe-56)?
Correct Answer: About 8.8 MeV
Question 28
Why does nuclear fusion require extremely high temperatures (thermonuclear reaction)?
Correct Answer: To provide high kinetic energy to overcome electrostatic repulsion between nuclei
Question 29
What is the composition of a nucleus containing atomic number Z and mass number A?
Correct Answer: Z protons and (A - Z) neutrons
Question 30
What is the nuclear force range roughly?
Correct Answer: About 1 to 2 femtometers (10⁻¹⁵ m)
Question 31
What is the main reason why heavy nuclei are radioactive and undergo alpha decay?
Correct Answer: Coulomb repulsion between excessive protons overcomes short-range nuclear attractive force
Question 32
What is the fraction of active radioactive nuclei remaining after 3 half-lives?
Correct Answer: 1 / 8 (or 12.5%)
Question 33
If a radioactive substance has half-life of 10 days, what fraction of the substance remains undecayed after 30 days?
Correct Answer: 1 / 8
Question 34
What is the internal structure of a neutron in terms of quarks?
Correct Answer: One up quark and two down quarks (udd)
Question 35
What is the internal structure of a proton in terms of quarks?
Correct Answer: Two up quarks and one down quark (uud)
Question 36
Which of the following units is most convenient for expressing atomic and nuclear masses?
Correct Answer: Unified atomic mass unit (u or amu)
Question 37
What is 1 u defined as?
Correct Answer: 1/12th of the mass of an unbound neutral carbon-12 atom at rest
Question 38
Why can't electrons exist inside the nucleus according to quantum mechanics (uncertainty principle)?
Correct Answer: The confinement energy required for an electron inside a 1 fm box would be vastly greater than ~20 MeV (electrons have ~0.5 MeV rest mass)
Question 39
What happens to atomic number Z and mass number A during alpha (α) decay?
Correct Answer: Z decreases by 2, A decreases by 4
Question 40
What happens to atomic number Z and mass number A during beta-minus (β⁻) decay?
Correct Answer: Z increases by 1, A remains unchanged
Question 41
What happens to atomic number Z and mass number A during gamma (γ) decay?
Correct Answer: Both Z and A remain unchanged (only energy state changes)
Question 42
What is the main purpose of a nuclear moderator in a reactor?
Correct Answer: To slow down fast neutrons to thermal equilibrium
Question 43
Which of the following is commonly used as a moderator in nuclear reactors?
Correct Answer: Heavy water (D₂O) and Graphite
Question 44
What is the atomic number Z of Uranium-235?
Correct Answer: 92
Question 45
What happens to the mass number and atomic number during beta-plus (β⁺) decay (positron emission)?
Correct Answer: Z decreases by 1, A remains unchanged
Question 46
What is electron capture?
Correct Answer: Nucleus captures an inner shell electron, converting a proton into a neutron
Question 47
What is the approximate binding energy of a deuteron (?²H)?
Correct Answer: 2.22 MeV (about 1.11 MeV per nucleon)
Question 48
Why are heavy nuclei unstable and prone to fission?
Correct Answer: Electrostatic repulsion among many protons exceeds short-range nuclear attraction in large volumes
Question 49
What is the range of mass number A for which nuclei are most stable?
Correct Answer: Between 30 and 170 (peak around 50-80)
Question 50
What is the active core material in an atomic bomb or nuclear fission reactor?
Correct Answer: Uranium-235 or Plutonium-239
Question 51
What is the name of the graph that shows binding energy per nucleon plotted against mass number?
Correct Answer: Binding energy curve
Question 52
What is the value of nuclear radius constant R₀ approximately?
Correct Answer: 1.2 × 10⁻¹⁵ m (1.2 fm)
Question 53
Which law is illustrated by the equation: Rate of decay = -λ N?
Correct Answer: Law of Radioactive Decay
Question 54
What is the half-life of a radioactive substance whose decay constant λ is 0.0693 per year?
Correct Answer: 10 years
Question 55
What is the probability of survival of a radioactive nucleus beyond its mean life (Ï„)?
Correct Answer: 1 / e (approx 36.8%)
Question 56
What is the fractional decrease in nuclei per unit time (- dN / (N dt)) called?
Correct Answer: Decay constant (λ)
Question 57
Which of the following forces is charge-independent (acts equally between proton-proton, neutron-neutron, and proton-neutron)?
Correct Answer: Nuclear force
Question 58
What happens to mass number during electron capture?
Correct Answer: Remains unchanged (Z decreases by 1)
Question 59
What is the binding energy per nucleon of a stable nucleus compared to an unstable one?
Correct Answer: Higher for stable nuclei
Question 60
Why are control rods necessary in a nuclear power plant?
Correct Answer: To prevent meltdown by regulating or shutting down the fission chain reaction
Question 61
What is the constituent particle family of both protons and neutrons?
Correct Answer: Nucleons (and fundamentally quarks)
Question 62
If a radioactive sample decays to 1/16th of its initial value in 40 days, what is its half-life?
Correct Answer: 10 days
Question 63
What is the total mass of nucleons compared to the mass of the nucleus (mass defect)?
Correct Answer: Mass of nucleons is always greater than the mass of the nucleus
Question 64
Which of the following is true regarding nuclear force exchange particles?
Correct Answer: Mediated by exchange of pi-mesons (pions)
Question 65
What is the shape of a stable nucleus typically considered to be?
Correct Answer: Approximately spherical
Question 66
Why does a free neutron decay outside the nucleus while a bound neutron inside a stable nucleus is stable?
Correct Answer: Because of energy state adjustments and binding energy conditions inside the nucleus
Question 67
What is the average lifetime (Ï„) of a radioactive substance related to half-life (T_1/2)?
Correct Answer: Ï„ = T_(1/2) / 0.693 ≈ 1.44 T_(1/2)
Question 68
Which nuclear reaction supplies energy in a hydrogen bomb?
Correct Answer: Uncontrolled nuclear fusion
Question 69
What is the energy released per fission of a Uranium-235 nucleus approximately?
Correct Answer: About 200 MeV
Question 70
What is the role of coolant in a nuclear reactor?
Correct Answer: To transfer heat produced by fission from core to steam generators to produce electricity
Question 71
What is the ratio of nuclear radii of two nuclei with mass numbers 64 and 27 (R_64 / R_27)?
Correct Answer: 4 / 3
Question 72
What is the ratio of nuclear volumes of two nuclei with mass numbers 125 and 8?
Correct Answer: 125 / 8
Question 73
Which type of nuclear reaction is responsible for energy generation in the core of young stars?
Correct Answer: Proton-proton chain fusion
Question 74
What does 'activity' of a radioactive sample mean?
Correct Answer: Number of disintegrations per second
Question 75
How does activity (A) of a radioactive sample change with time t?
Correct Answer: A(t) = A₀ e^(-λt)
Question 76
Why are heavy elements like uranium unable to maintain stability without radioactive decay?
Correct Answer: The repulsive electrostatic forces between large numbers of protons exceed the attractive nuclear forces
Question 77
What is the main advantage of controlled nuclear fusion over nuclear fission for power generation?
Correct Answer: Abundant fuel (deuterium from water) and minimal long-lived radioactive waste
Question 78
What is the neutrino (or antineutrino) particle characterized by?
Correct Answer: Zero charge, extremely small mass, and weak interaction with matter
Question 79
Why was the neutrino postulated by Wolfgang Pauli in beta decay?
Correct Answer: To account for the apparent violation of energy and angular momentum conservation in beta decay
Question 80
What is the approximate age of Earth estimated using radioactive dating techniques?
Correct Answer: About 4.5 billion years
Question 81
What is Carbon-14 dating used for?
Correct Answer: Estimating the age of organic fossils and ancient biological remains
Question 82
What is the unit of nuclear cross-section (area)?
Correct Answer: Barn (1 barn = 10⁻²⁸ m²)
Question 83
What happens during the beta-plus decay of a nucleus?
Correct Answer: A proton converts into a neutron, emitting a positron and a neutrino
Question 84
What is the rest mass of a positron compared to an electron?
Correct Answer: Equal in mass (antiparticle of electron with positive charge)
Question 85
What is the main danger associated with nuclear power plant operations?
Correct Answer: Disposal of long-lived radioactive waste and potential reactor accidents
Question 86
What is a breeder reactor?
Correct Answer: A nuclear reactor that produces more fissile material than it consumes
Question 87
Why can nuclear fusion not be easily harnessed for commercial power generation yet?
Correct Answer: Because maintaining extreme plasma temperatures and confinement is technologically extremely difficult
Question 88
What is the atomic mass unit expressed in MeV/c²?
Correct Answer: 931.5 MeV/c²
Question 89
What is the rest mass energy of an electron in MeV?
Correct Answer: 0.511 MeV
Question 90
What is the quark composition of a proton?
Correct Answer: uud (two up quarks and one down quark)
Question 91
What is the electrical charge of an up quark (u)?
Correct Answer: + (2/3) e
Question 92
What is the electrical charge of a down quark (d)?
Correct Answer: - (1/3) e
Question 93
What happens to the total number of nucleons (A) in a nuclear reaction?
Correct Answer: It is conserved
Question 94
What is the ratio of nuclear radii for two nuclei with mass numbers 1 and 216 (R_1 / R_216)?
Correct Answer: 1 / 6
Question 95
What does a nuclear binding energy curve sloping downward for very heavy nuclei indicate?
Correct Answer: Heavy nuclei can release energy by undergoing nuclear fission
Question 96
What does a steep upward slope of the binding energy curve at low mass numbers (A < 30) indicate?
Correct Answer: Light nuclei can release energy by undergoing nuclear fusion
Question 97
Which particle is liberated when a free neutron decays spontaneously outside a nucleus?
Correct Answer: A proton, an electron, and an antineutrino
Question 98
What is the approximate mean life (Ï„) if half-life of a radioactive isotope is 100 days?
Correct Answer: 144.3 days
Question 99
What is the main reason why alpha particles are emitted by heavy radioactive nuclei rather than individual protons or neutrons?
Correct Answer: Because the alpha particle (He-4 nucleus) has an exceptionally high binding energy, making its formation energetically favorable
Question 100
What does the nuclear density signify about the distribution of matter inside nuclei across different elements?
Correct Answer: It shows that nuclear matter has a uniform packing and density, largely independent of the specific element
