Question 1

Nuclear mass–energy equivalence: numerically, 1 atomic mass unit (1 amu) corresponds to approximately how much energy?

Accepted Answer

Introduction: Converting between atomic mass units and energy is routine in nuclear physics and engineering. The amu-to-MeV conversion arises from E = m * c^2, enabling quick estimation of reaction Q-values and binding energies. Given Data / Assumptions: Use the widely accepted conversion: 1 u ≈ 931.5 MeV (often rounded to 931 MeV in MCQs). We need only the order-of-magnitude and correct unit. Concept / Approach: The rest energy corresponding to 1 atomic mass unit is about 931.5 MeV. In multiple-choice contexts, 931 MeV is the standard rounded value. This conversion is essential for analyzing nuclear reactions and decay energetics without detailed SI calculations. Step-by-Step Solution: Recall: 1 u ≈ 1.6605 × 10^-27 kg.Compute energy using E = m * c^2 → ≈ 1.4924 × 10^-10 J.Convert joules to eV (1 eV = 1.602 × 10^-19 J) → ≈ 9.315 × 10^8 eV ≈ 931 MeV. Verification / Alternative check: Standard nuclear data tables list 1 u ≈ 931.494 MeV, confirming the rounded figure. Why Other Options Are Wrong: 9.31 MeV or 931 eV: off by two or six orders of magnitude, respectively. 931 J: incorrect unit; the energy scale in nuclear physics is MeV, not joules for quick tabulations. 93.1 keV: off by a factor of 10,000. Common Pitfalls: Mistaking eV, keV, MeV prefixes or mixing energy in eV with mass in amu without proper conversion. Final Answer: 931 MeV

Question 2

Order-of-magnitude nuclear sizes: what is the approximate ratio of the volume of an atom to the volume of its nucleus?

Accepted Answer

Introduction: Comparing atomic and nuclear dimensions illustrates why most of the atom is empty space. This scale difference underpins models of electron orbitals, scattering experiments, and the conceptual separation between nuclear and electronic phenomena. Given Data / Assumptions: Typical atomic radius ~ 10^-10 m (or 10^-8 cm). Typical nuclear radius ~ 10^-15 m (or 10^-12 cm). Volumes scale with the cube of linear dimension. Concept / Approach: If r_atom / r_nucleus ≈ 10^5 in SI metres, the volume ratio is (10^5)^3 ≈ 10^15. However, using cgs common textbook radii (10^-8 cm vs 10^-12 cm) gives a linear ratio of 10^4 and a volume ratio of 10^12. Many introductory references and MCQs adopt this cgs-based comparison, yielding 10^12. Step-by-Step Solution: Choose representative radii in cm: atom ~10^-8 cm; nucleus ~10^-12 cm.Compute linear ratio: 10^-8 / 10^-12 = 10^4.Convert to volume ratio: (10^4)^3 = 10^12. Verification / Alternative check: Using SI radii (1 × 10^-10 m and 1 × 10^-15 m) gives 10^15; the discrepancy reflects the variability of quoted “typical” sizes. For standardized MCQs, 10^12 is a commonly accepted answer. Why Other Options Are Wrong: 10^-12 and 10^-8: These represent tiny ratios, not the enormous atomic-to-nuclear volume ratio. 10^8: Too small compared to typical estimates. 10^5: This is close to the linear ratio (radius), not volume. Common Pitfalls: Mixing linear and volumetric ratios or confusing cgs and SI “typical” radii without cubing for volume. Final Answer: 10^12

Question 3

From the following materials commonly found in reactor systems, which one is used specifically as a moderator (i.e., to slow down neutrons)?

Accepted Answer

Introduction: Moderators reduce neutron energies to the thermal range, improving the fission probability in certain fuels (e.g., U-235). Distinguishing moderators from absorbers and structural materials is a key competency in reactor design. Given Data / Assumptions: Typical moderator choices: light water, heavy water, graphite. Absorber/control materials: cadmium, boron compounds. Cladding/structure: zircaloy, stainless steel. Concept / Approach: An effective moderator exhibits strong scattering with minimal absorption. Graphite (carbon) fulfills this role and has been used in many reactor designs. Cadmium and boron compounds are strong absorbers for control/shutdown. Zircaloy is favored for fuel cladding due to low absorption and good corrosion resistance, not as a moderator. Stainless steel is primarily structural. Step-by-Step Solution: Identify moderator: Graphite is a classic moderator.Exclude absorbers: Cadmium and boron carbide are control/poison materials.Exclude structural/cladding: Zircaloy and stainless steel are not used to moderate. Verification / Alternative check: Historical and modern reactors (e.g., graphite-moderated designs) demonstrate graphite’s moderating role. Why Other Options Are Wrong: Cadmium/boron carbide: Excessive absorption kills reactivity; used for control rods. Zircaloy/stainless steel: Employed for mechanical reasons; not intended to slow neutrons. Common Pitfalls: Assuming low-absorption cladding like zircaloy is also a moderator. While it does not strongly absorb, it is not suitable for deliberate neutron slowing compared to graphite or water. Final Answer: Graphite

Question 4

Fertile vs. fissile: which of the following is NOT a fertile material in the nuclear fuel cycle?

Accepted Answer

Introduction: Fertile nuclides can absorb a neutron and transmute into fissile nuclides. Distinguishing fertile from fissile isotopes is essential for fuel-cycle strategy and breeder-reactor concepts. Given Data / Assumptions: Common fertile nuclides: Th-232, U-238 (convert to U-233 and Pu-239 respectively). Fissile nuclides: U-233, U-235, Pu-239, etc. Concept / Approach: U-233 is already fissile, produced from neutron capture by Th-232 followed by beta decays. Therefore, U-233 is not fertile. Th-232 and U-238 are classic fertile materials. Some other heavier plutonium isotopes (e.g., Pu-240) are predominantly fertile rather than fissile. Step-by-Step Solution: Identify the fissile candidate: U-233 is fissile.Recognize the classic fertile isotopes: Th-232 and U-238.Hence, the one that is NOT fertile is U-233. Verification / Alternative check: Fuel-cycle diagrams confirm Th-232 → U-233 breeding and U-238 → Pu-239 breeding, verifying the classification. Why Other Options Are Wrong: Th-232 and U-238: canonical fertile nuclides. Pu-240: largely fertile; poor fissile performance with thermal neutrons. “None of these” would imply all are fertile, which is incorrect because U-233 is fissile. Common Pitfalls: Confusing “fissile” (readily fissions with thermal neutrons) with “fertile” (neutron capture leads to fissile product). Final Answer: U-233

Question 5

Purpose of research reactors: what is the primary objective for operating research (non-power) nuclear reactors?

Accepted Answer

Introduction: Research reactors are specialized facilities optimized for intense neutron fields rather than power production. They underpin materials testing, neutron activation analysis, isotope production, and fundamental neutron science. Given Data / Assumptions: Research reactors are typically low to medium thermal power. Core and reflector geometries maximize neutron flux in beam ports and irradiation positions. Flux values commonly quoted: around 10^12–10^13 neutrons/cm^2·s (and higher for some advanced facilities). Concept / Approach: The design focus is neutron economy and accessibility (beam tubes, irradiation facilities) rather than thermodynamic conversion to electricity. While isotope production can be a major mission, the defining characteristic is providing controlled, high neutron flux for experiments and material exposure. Step-by-Step Solution: Identify mission: high neutron flux for studies and irradiations.Flux magnitude aligns with typical research reactor capabilities.Therefore, option (a) matches the core purpose. Verification / Alternative check: Descriptions of well-known research reactors (e.g., TRIGA, MURR, HFIR) emphasize neutron flux and experimental facilities over electric power generation. Why Other Options Are Wrong: Neutron acceleration to relativistic speeds is the domain of particle accelerators, not reactors. Power generation is the mission of power reactors, not research reactors. Isotope production is important but not the sole defining objective; many research programs focus on materials and fundamental science. Exclusive waste transmutation is not the primary commercial product of research reactors. Common Pitfalls: Assuming “reactor” always implies electricity generation. Research reactors are optimized differently, prioritizing neutron availability and experimental access. Final Answer: Producing high neutron flux (≈10^12–10^13 neutrons/cm^2·s) for experiments and irradiation studies

Question 6

Radioactive decay and half-life: A certain radioisotope has a half-life of 100 years. If a sample is stored for 400 years (i.e., four half-life periods), what fraction of the original mass will remain at the end of 400 years?

Accepted Answer

Introduction / Context: Radioactive decay follows first-order kinetics. The concept of half-life tells us how long it takes for half of the nuclei in a sample to undergo decay. This question checks whether you can translate a given half-life into the remaining fraction after multiple half-life intervals, a core skill in nuclear chemistry, radiological safety, and environmental dose assessment. Given Data / Assumptions: Half-life (t1/2) = 100 years. Total elapsed time = 400 years. Decay is purely radioactive (no chemical loss or addition) and follows first-order decay law. We report the remaining mass as a fraction of the initial mass. Concept / Approach: The fraction of material remaining after n half-lives is (1/2)^n. Alternatively, the decay law is N(t) = N0 * 2^(−t / t1/2). Because only fractions are asked, absolute amounts cancel out. This avoids the need for decay constants in this simple case. Step-by-Step Solution: Compute number of half-lives: n = 400 / 100 = 4.Remaining fraction after n half-lives: f = (1/2)^n = (1/2)^4.Evaluate: (1/2)^4 = 1/16.Thus, after 400 years, one-sixteenth of the original mass remains. Verification / Alternative check: Use the exponential form: N/N0 = 2^(−t/t1/2) = 2^(−4) = 1/16, which confirms the result. Why Other Options Are Wrong: 1/2 and 1/4 correspond to 1 and 2 half-lives, not 4. 1/8 corresponds to 3 half-lives (300 years), not 400 years. Common Pitfalls: Dividing the mass by 4 instead of halving it four times (linear versus exponential thinking). Confusing the decay constant with half-life; here the half-life method is faster. Using percent instead of fraction; the problem explicitly asks for a fractional answer. Final Answer: 1/16

Question 7

Isotopes of hydrogen in nuclear science: Which one of the following is the radioactive isotope of hydrogen frequently used as a tracer in fusion and environmental studies?

Accepted Answer

Introduction / Context: Hydrogen exists as several isotopes with different numbers of neutrons. Understanding which isotope is radioactive is essential for topics such as fusion reactions, radiolabeled tracers, and health physics. This question focuses on identifying the radioactive hydrogen isotope used widely in research and technology. Given Data / Assumptions: Three common isotopic forms: protium (¹H), deuterium (²H or D), and tritium (³H or T). Ortho-hydrogen refers to a spin isomeric form of H2, not an isotope. We need the isotope that is radioactive. Concept / Approach: Isotopes share the same number of protons but differ in neutrons. Deuterium (one neutron) is stable and used in heavy water. Tritium (two neutrons) is unstable and radioactive, undergoing beta decay to helium-3. Ortho/para hydrogen describe nuclear spin configurations (parallel vs. antiparallel) in molecular hydrogen and are not isotopic distinctions. Step-by-Step Solution: Identify isotopes: D (stable), T (radioactive).Recognize that ortho-hydrogen is a spin isomer, not an isotope.Therefore, the radioactive isotope is tritium (³H). Verification / Alternative check: Nuclear data tables list tritium half-life ≈ 12.3 years with low-energy beta emission, confirming its radioactivity and utility as a tracer and in self-luminous devices. Why Other Options Are Wrong: Deuterium: stable; used in D2O and fusion targets but not radioactive. Ortho-hydrogen: not an isotope. “None of these” is incorrect because tritium is indeed radioactive. Common Pitfalls: Confusing isotopes (D, T) with spin isomers (ortho/para). Assuming all heavy forms of hydrogen are radioactive; deuterium is stable. Final Answer: Tritium

Question 8

Coolant circulation in liquid-metal fast systems: For recirculating molten sodium in a liquid-metal-cooled nuclear reactor, which pump type is most appropriate due to sodium’s high electrical conductivity and operating temperature?

Accepted Answer

Introduction / Context: Liquid-metal-cooled reactors (especially fast reactors) often use sodium as a coolant because of its excellent thermal properties. Pumping liquid metals poses unique challenges: high temperature, reactivity, and the need to avoid moving seals and bearings in hot, reactive fluids. This question examines the pump technology best suited to such conditions. Given Data / Assumptions: Coolant: molten sodium (electrically conductive, low viscosity, reactive with water/air). Continuous recirculation required in primary/secondary loops. High reliability and minimal leakage paths are desired. Concept / Approach: Electromagnetic pumps operate on the Lorentz force: a conductive fluid moving through a magnetic field experiences a body force that drives flow when an electric current is imposed. This design avoids rotating components in contact with the liquid metal, reducing mechanical wear and leakage risks at elevated temperatures. Conventional centrifugal or reciprocating pumps have shafts, seals, and bearings that become problematic in hot sodium service. Step-by-Step Solution: Assess sodium properties: conductive, hot, reactive.Match to pump principle: electromagnetic pumping provides contactless driving force.Conclude: choose an electromagnetic pump for molten sodium recirculation. Verification / Alternative check: Fast-reactor literature documents use of both electromagnetic and specially engineered mechanical pumps; however, electromagnetic pumps are particularly favored for leak-tight primary systems. Why Other Options Are Wrong: Reciprocating pumps: pulsating flow and seal complexity. Centrifugal/volute pumps: require shaft seals and bearings in hostile environments; used in some designs but not the typical best fit for sodium primary loops compared to electromagnetic options. Common Pitfalls: Ignoring electrical conductivity; EM pumping relies on this property. Assuming room-temperature pump choices apply directly to liquid metals. Final Answer: Electromagnetic pump

Question 9

Tarapur Atomic Power Station (TAPS) facts, clarified: Which combination of statements about TAPS, India, is correct? (Choose the option that makes exactly one correct overall choice.)

Accepted Answer

Introduction / Context: Exam questions sometimes condense complex facility histories into short statements. Tarapur Atomic Power Station (TAPS) has multiple units across different generations. This item tests factual recall while avoiding the trap of an overstated capacity figure often seen in older summaries. Given Data / Assumptions: We focus on the original TAPS Units 1 and 2 (BWRs) and their historical milestones. We need a combination that is factually consistent without introducing multiple correct options. Concept / Approach: Historically, TAPS-1 and TAPS-2 are boiling water reactors (BWRs) supplied under U.S. collaboration. They are widely cited as India's first commercial nuclear power reactors, with first criticality occurring in 1969. The commonly quoted initial net capacity for these two units was about 2 × 160 MW ≈ 320 MW, not 400 MW. Hence, a capacity claim of 400 MW for Units 1 and 2 is inaccurate for the historical context. Step-by-Step Solution: Evaluate (a): Correct — two American-design BWRs.Evaluate (b): Incorrect — early capacity ≈ 320 MW for Units 1 and 2, not 400 MW.Evaluate (c): Correct — India's first power reactor site with first criticality in 1969.Therefore, the unique correct option is the combined statement: (a) and (c) only. Verification / Alternative check: Historical records list TAPS-1 and TAPS-2 as early BWRs with first criticality in 1969; capacity figures around 160 MW per unit are standard in reference texts. Why Other Options Are Wrong: (a) alone and (c) alone would give multiple correct options; the question requires a single combined choice. (b) is factually incorrect for the original pair. The combined option in (d) resolves the ambiguity precisely. Common Pitfalls: Memorizing rounded capacities (e.g., “~400 MW”) without checking unit-wise ratings. Confusing later TAPS Units 3 and 4 (540 MW PHWRs) with the original BWR units. Final Answer: Statements (a) and (c) only are correct.

Question 10

In nuclear reactions, which quantities are conserved when writing and balancing reaction equations?

Accepted Answer

Introduction / Context: Balancing nuclear reaction equations requires conservation principles analogous to balancing chemical equations. Instead of atoms and molecules, we track nucleons and charge to ensure physical consistency before and after a reaction event such as decay, fission, or fusion. Given Data / Assumptions: Reaction written as target + projectile → products + particles (e.g., n, p, α, β). Relativistic mass–energy equivalence applies, but bookkeeping uses discrete mass number (A) and atomic number (Z) for balance. Concept / Approach: The mass number A (total nucleons = protons + neutrons) and atomic number Z (protons = net charge in units of e) must be conserved across the equation. Energy and momentum are also conserved, but the tabular balancing typically enforces A and Z conservation explicitly, accounting for emitted particles (e.g., α has A = 4, Z = 2; β− has A = 0, Z = −1; γ has A = 0, Z = 0). Step-by-Step Solution: Write all nuclides with A (superscript) and Z (subscript).Sum A on reactant side and match to product side.Sum Z on reactant side and match to product side including emitted/absorbed particles.Confirm energy/momentum consistency separately through Q-value if needed. Verification / Alternative check: Example: ²³⁵U (A=235, Z=92) + n (A=1, Z=0) → ¹⁴¹Ba (A=141, Z=56) + ⁹²Kr (A=92, Z=36) + 3 n (3*1, 0). A: 236 → 236; Z: 92 → 92, balanced. Why Other Options Are Wrong: A only or Z only: incomplete; both must balance.Neither: violates fundamental conservation.Neutron count only: not generally conserved; neutrons can be emitted/absorbed. Common Pitfalls: Forgetting to include the charge of β particles in Z balance.Confusing conservation of A with conservation of rest mass (mass defect converted to energy is allowed). Final Answer: Both mass number (A) and atomic number (Z)

Question 11

In Indian nuclear fuel operations, where is the Uranium Corporation of India Limited (UCIL) site engaged in mining and concentration of uranium ore located?

Accepted Answer

Introduction / Context: India's nuclear fuel cycle begins with mining and concentration of uranium ore before further processing and fuel fabrication. Knowing the locations and roles of key facilities, such as those operated by Uranium Corporation of India Limited (UCIL), is a common general knowledge topic in chemical, nuclear, and general engineering examinations. Given Data / Assumptions: Question asks for the UCIL site engaged in mining and concentration of uranium ore. Options include several well-known Indian nuclear or coastal locations, but only one corresponds to UCIL's long-established uranium mining and mill operations. No calculations are required; this is a factual identification task. Concept / Approach: UCIL historically operates uranium mining and processing at Jadugoda in the Singhbhum district (present-day Jharkhand). Other nuclear sites in the options serve different roles: Kalpakkam and Tarapur are primarily associated with nuclear power and research facilities; Alwaye (Aluva) is known for other chemical/mineral activities; Gopalpur coast relates to a coastal area in Odisha but not UCIL's uranium mines. Therefore, among the listed places, Jadugoda uniquely matches UCIL's uranium mining and concentration operations. Step-by-Step Solution: Identify which option corresponds to UCIL's uranium mines and processing mill.Recognize that Jadugoda (Singhbhum belt) is India's classic uranium mining district.Exclude sites known primarily for power reactors or coastal geography unrelated to UCIL mining.Select Jadugoda, Jharkhand as the correct location. Verification / Alternative check: Standard nuclear energy overviews and Indian energy geography consistently list Jadugoda as the historical uranium mining and processing hub under UCIL, with ore concentration occurring before transport for further steps in the fuel cycle. Why Other Options Are Wrong: Alwaye, Kerala: Not UCIL's uranium mine/mill site.Kalpakkam, Tamil Nadu: Known for reactors and research, not uranium mining.Gopalpur coast, Odisha: Coastal location; not UCIL's uranium mine.Tarapur, Maharashtra: Nuclear power station area, not a UCIL mine. Common Pitfalls: Confusing reactor or research locations with upstream mining and concentration sites. Remember that mining districts like Jadugoda are distinct from reactor complexes located in other states. Final Answer: Jadugoda, Jharkhand

Question 12

Natural uranium composition check: which of the following isotopes is not present in naturally occurring uranium?

Accepted Answer

Introduction / Context: Natural uranium is a mixture of isotopes with specific fractional abundances. Recognizing which isotopes occur naturally versus those that are produced artificially is fundamental in nuclear science, fuel cycle discussions, and reactor engineering basics. Given Data / Assumptions: Natural uranium is dominated by one major isotope with two additional minor constituents. Some uranium isotopes are produced through neutron capture or as decay products during reactor operations rather than being present in ores as-mined. This is a factual recall question. Concept / Approach: Natural uranium consists primarily of U-238 (about 99% by atom), a smaller proportion of U-235 (about 0.7%), and a trace of U-234 (much less than 1%). Isotopes like U-232 and U-236 are generally not present in natural uranium; U-236 is typically formed via neutron capture on U-235 inside reactors, and U-232 can arise in certain thorium–uranium fuel sequences or reprocessed materials, not as a natural ore constituent. Therefore, among the listed options, U-232 is not present in natural uranium. Step-by-Step Solution: Recall natural uranium isotopes: U-238, U-235, U-234.Identify isotopes formed during irradiation or special decay chains (e.g., U-232, U-236).Conclude U-232 is not a natural component of uranium ores. Verification / Alternative check: Introductory nuclear engineering texts list the natural abundances and note that U-236 and U-232 are signatures of irradiated/reprocessed material, not freshly mined ore. Why Other Options Are Wrong: U-238: Major natural isotope.U-234: Present in trace amounts via decay of U-238.U-235: Minor but crucial fissile isotope in natural uranium.U-236: Typically produced in reactors, but the question asks which is not present; U-232 is the clearest correct choice here. Common Pitfalls: Confusing U-236 with U-234; the former is not naturally present in significant amounts, whereas U-234 is a recognized trace constituent of natural uranium. Final Answer: U-232

Question 13

Pressurised Water Reactor (PWR): which statement correctly describes the role of pressure in the primary coolant loop?

Accepted Answer

Introduction / Context: Pressurised Water Reactors (PWRs) are a dominant light-water reactor type worldwide. Understanding their fundamental thermal-hydraulic principle clarifies how heat is transferred safely from fuel to secondary systems while avoiding boiling in the core region. Given Data / Assumptions: We are comparing descriptions of fuel, moderator, and coolant behavior in a PWR. PWRs use enriched uranium fuel, light water as both moderator and coolant, and a separate steam generator. The primary loop is maintained at high pressure. Concept / Approach: In a PWR, the primary coolant is light water kept at very high pressure so that it remains subcooled (no bulk boiling) while flowing through the core. Heat is carried to steam generators where a separate secondary loop boils to produce steam for turbines. This design contrasts with BWRs, where boiling occurs in the core, and with heavy-water reactors (e.g., PHWRs) that can use natural uranium and heavy water. Therefore, the defining correct statement is that the primary coolant in a PWR is pressurised to prevent bulk boiling in the core. Step-by-Step Solution: Identify PWR characteristics: light water coolant/moderator, high pressure, separate steam generator.Evaluate each option against known PWR features.Select the statement about pressurisation preventing bulk boiling. Verification / Alternative check: Standard nuclear engineering references describe PWR operating pressures on the order of tens of bar, ensuring subcooled operation in the core and phase change only in the secondary side. Why Other Options Are Wrong: Natural uranium with heavy water: describes PHWR, not PWR.Coolant boils in the core: describes BWR behavior, not PWR.No moderator required: incorrect; PWR uses light water as moderator.Thorium with CO2: not a PWR configuration. Common Pitfalls: Confusing PWR with BWR or PHWR; always check whether boiling occurs in-core and what moderator is used. Final Answer: Coolant water is highly pressurised to prevent bulk boiling in the core.

Question 14

Heavy water (D2O) production in India: which of the following sites is NOT a location of a heavy water plant?

Accepted Answer

Introduction / Context: Heavy water (D2O) is an essential moderator and coolant in certain reactor types (e.g., PHWRs). India established heavy water plants at multiple industrial hubs to ensure supply. Being able to identify authentic sites is a frequent exam theme in energy engineering and GK sections. Given Data / Assumptions: Options list Indian industrial locations; several are known heavy water plant sites. We must select the location that is not associated with a heavy water plant. No numerical work is required. Concept / Approach: India has historically operated heavy water plants at places such as Kota (Rajasthan), Tuticorin (Tamil Nadu), Talcher (Odisha), Manuguru (Telangana), Thal (Maharashtra), and Vadodara (Gujarat). Among the options given, Ramagundam is known for major power and fertilizer installations but is not the site of a heavy water plant—the heavy water facility in that region is at Manuguru, not Ramagundam. Therefore, the correct choice is Ramagundam. Step-by-Step Solution: List known heavy water plant sites.Cross-check each option with the known list.Identify Ramagundam as not hosting a heavy water plant. Verification / Alternative check: Energy-industry directories and Indian nuclear fuel cycle summaries consistently list the above heavy water plant locations; Ramagundam does not appear as such. Why Other Options Are Wrong: Talcher: Recognized heavy water plant site.Tuticorin: Recognized heavy water plant site.Kota: Recognized heavy water plant site.Vadodara: Recognized heavy water plant site (also called Baroda). Common Pitfalls: Confusing regional industrial names (e.g., Manuguru vs nearby towns). Always match the exact plant location used in official references. Final Answer: Ramagundam

Question 15

History of nuclear science: the discovery of the phenomenon of radioactivity is credited to which scientist?

Accepted Answer

Introduction / Context: Understanding milestones in nuclear science provides context for modern engineering applications. Radioactivity, the spontaneous emission from unstable nuclei, underpins nuclear energy, medical diagnostics, and radiation protection standards. Identifying who first discovered it is a staple general knowledge item. Given Data / Assumptions: Question asks for the original discoverer of radioactivity. Several eminent physicists worked on related phenomena around the same time. No computation is involved. Concept / Approach: Henri Becquerel discovered natural radioactivity in 1896 while investigating phosphorescent uranium salts and their ability to fog photographic plates without exposure to sunlight. Marie and Pierre Curie subsequently isolated radioactive elements (polonium, radium) and advanced the field. Roentgen discovered X-rays (not radioactivity) in 1895, and J. J. Thomson identified the electron. Ernest Rutherford later characterized alpha and beta radiation and proposed the nuclear atom model, but he did not make the original discovery of radioactivity. Step-by-Step Solution: Recall chronology: Roentgen (X-rays, 1895) → Becquerel (radioactivity, 1896) → Curies (new radioactive elements).Match each scientist to their discovery.Select Henri Becquerel for radioactivity. Verification / Alternative check: Standard physics histories consistently credit Becquerel with the discovery and the Curies with subsequent isolation/exploration of strongly radioactive substances. Why Other Options Are Wrong: Marie Curie: Pioneered research and element isolation but did not first discover radioactivity.Roentgen: Discovered X-rays, a separate phenomenon.J. J. Thomson: Discovered the electron.Ernest Rutherford: Characterized radiation types and nuclear structure later. Common Pitfalls: Conflating X-rays with radioactivity or attributing the first discovery to the Curies due to their fame and contributions soon after Becquerel's findings. Final Answer: Henri Becquerel

Question 16

In nuclear fission, which form of energy accounts for the largest fraction of the total energy released per fission event?

Accepted Answer

Introduction / Context: Understanding the energy partition in nuclear fission is essential for reactor heat balance, shielding, and safety analysis. A typical fission of U-235 releases around 200 MeV, distributed among various carriers such as fragment kinetic energy, gamma rays, neutrons, and decay energy. Given Data / Assumptions: We focus on the immediate and subsequent energy forms following a fission event. Ballpark values: the largest share appears as kinetic energy of the two main fission fragments. No numerical calculation is required beyond qualitative comparison. Concept / Approach: When a heavy nucleus splits, the two nascent fission fragments repel each other due to strong Coulomb forces, acquiring substantial kinetic energy. This fragment kinetic energy is rapidly converted into heat in the fuel. Smaller fractions are carried by prompt gamma rays, kinetic energy of neutrons, and later by beta and gamma emissions from radioactive decay of fission products. Antineutrinos carry away energy but do not deposit it in the reactor core. Thus, the largest single component is the kinetic energy of the fission products. Step-by-Step Solution: List the main energy carriers: fragment kinetic energy, neutron kinetic energy, prompt gammas, delayed decay energy, antineutrinos.Recall typical partitioning: fragment kinetic energy is the dominant portion.Select the option that names fission product kinetic energy as the maximum contributor. Verification / Alternative check: Introductory reactor physics texts and heat balance tables consistently show fragment kinetic energy forming the majority share (often on the order of 160+ MeV out of ~200 MeV for U-235 fission), with other components much smaller. Why Other Options Are Wrong: Radioactive decay of fission products: significant but smaller than fragment kinetic energy.Instantaneous gamma rays: contribute a modest fraction.Neutron kinetic energy: a relatively small portion.Antineutrinos: energy is not recovered as heat; they escape. Common Pitfalls: Overestimating the role of prompt gammas or decay heat relative to the dominant fragment kinetic energy in immediate core heating. Final Answer: Kinetic energy of fission products (heavy fragments)

Question 17

Origin of solar energy: the Sun's sustained energy output primarily results from which kind of nuclear reaction?

Accepted Answer

Introduction / Context: Solar energy reaching Earth originates from processes in the Sun's core. Knowing the underlying reaction type is essential background for topics ranging from astrophysics to renewable energy engineering. Given Data / Assumptions: Focus is on the primary nuclear process in stellar cores. The Sun is a main-sequence star with hydrogen-rich composition. High temperature and pressure conditions enable specific nuclear reactions. Concept / Approach: In stars like the Sun, extreme core temperatures and pressures enable thermonuclear fusion—light nuclei (primarily hydrogen isotopes) fuse to form helium, releasing energy due to the mass-to-energy conversion described by E = m * c^2. This is distinct from fission (splitting heavy nuclei) and from chemical combustion, which cannot account for the Sun's energy scale or longevity. Radioactive decay also cannot supply the Sun's vast continuous output over billions of years. Step-by-Step Solution: Identify candidate processes: fission, combustion, fusion, decay.Recall stellar models: main-sequence stars generate energy by fusing hydrogen into helium.Select thermonuclear fusion as the governing mechanism. Verification / Alternative check: Standard astrophysics descriptions detail the proton–proton chain as the dominant mechanism in the Sun, consistent with observed neutrino fluxes and stellar evolution models. Why Other Options Are Wrong: Fission: Not the primary mechanism in the Sun.Combustion: Chemical energy is negligible compared to nuclear processes in stars.None of these: Incorrect because fusion is applicable.Radioactive decay: Insufficient to explain solar luminosity. Common Pitfalls: Confusing fusion with fission due to similar terminology; remember that stars synthesize heavier elements from lighter ones through fusion. Final Answer: Thermonuclear fusion reactions

Question 18

Which statement is correct regarding elementary particles and nuclear radiation characteristics?

Accepted Answer

Introduction / Context: Basic nuclear and particle physics concepts include particle identities and comparative properties of emitted radiations (alpha, beta, gamma). These properties determine ionisation behavior, penetration, and detection methods, which are central to radiation protection and instrumentation. Given Data / Assumptions: We compare truthfulness of statements about positrons and the relative characteristics of alpha, beta, and gamma radiation. Vacuum propagation speeds and ionising abilities are standard textbook facts. No computation is necessary. Concept / Approach: The positron is indeed the electron's antiparticle; it has the same mass but positive charge. Alpha particles (helium nuclei) are massive and doubly charged, leading to very high ionising power but low penetration and speeds well below light. Beta particles are electrons or positrons with lower ionising power than alpha but higher than gamma in many media. Gamma rays are uncharged photons and move at light speed in vacuum, exhibiting the greatest penetration and least ionising power among the three on a per-path basis. Step-by-Step Solution: Check particle–antiparticle relation: positron ↔ electron (true).Assess alpha decay effect on neutron/proton: both N and Z decrease by 2; the ratio does not increase markedly and can slightly decrease for heavy nuclei.Compare ionising powers: alpha > beta > gamma; statement that beta exceeds alpha is false.Speeds: gamma travels at c; alpha cannot exceed this; thus the claim alpha faster than gamma is false.Charge of gamma: photons are neutral; claiming opposite charge to electrons is false. Verification / Alternative check: Introductory nuclear physics tables list positron as e+ and confirm the qualitative ordering of ionisation and penetration for alpha, beta, gamma radiations. Why Other Options Are Wrong: Alpha decay increasing N/Z markedly: not generally correct; both N and Z drop by 2.Beta ionising > alpha: reverses the usual order.Alpha faster than gamma: impossible; gamma travels at the speed of light in vacuum.Gamma charged: incorrect; gamma photons are neutral. Common Pitfalls: Confusing penetration with ionisation. High ionisation (alpha) does not mean high penetration; in fact, it usually implies the opposite due to rapid energy loss. Final Answer: A positron is the antiparticle of an electron.

Question 19

Atomic and nuclear scales: identify the correct statement about ions, sizes, and stable nucleus composition.

Accepted Answer

Introduction / Context: Understanding orders of magnitude for atomic and nuclear dimensions, as well as correct ion definitions, is foundational in chemistry and nuclear engineering. These quantities explain why atoms are largely empty space compared to their dense nuclei and clarify basic terminology for charged species. Given Data / Assumptions: Nuclear radii are orders of magnitude smaller than atomic sizes. Cations and anions form via electron loss or gain, respectively. Stable nuclei have varying proton-to-neutron ratios depending on mass number. Concept / Approach: Atomic sizes are on the order of angstroms, about 10^-8 cm. Nuclear radii are roughly femtometre scale, often quoted around 10^-13 to 10^-12 cm depending on the nucleus; as an order-of-magnitude statement, 10^-12 cm is an acceptable scale indicator in many textbooks. Ion formation is defined by electron transfer: loss yields cations (positive), gain yields anions (negative). The proton-to-neutron ratio for stability is not fixed at 2:1; it is near 1:1 for light nuclei and shifts for heavier nuclei. Step-by-Step Solution: Compare scales: atomic size (~10^-8 cm) vs nuclear size (~10^-12 to 10^-13 cm).Evaluate ion statements: loss → cation (not negative ion); gain → anion (not cation).Check stability ratio claim: no universal 2:1 rule; varies with mass number.Confirm that removing electrons does not change nucleon count (protons + neutrons) in the nucleus. Verification / Alternative check: Introductory physical chemistry and nuclear physics references consistently present these orders of magnitude and definitions, supporting the correctness of the size comparison statement. Why Other Options Are Wrong: Loss → negative ions: incorrect; loss gives positive ions.Gain → cations: incorrect; gain gives anions.Proton-to-neutron ratio 2:1: not general; varies by element and mass number.Electron removal changes nucleons: false; nucleons are unaffected by electron transfer. Common Pitfalls: Mixing up signs of ions and conflating atomic radius scales with nuclear radius scales. Keep powers of ten explicit to avoid confusion. Final Answer: A typical nuclear radius is about 10^-12 cm, while atomic size is about 10^-8 cm.

Question 20

Atomic size benchmark: the linear size (diameter scale) of a typical atom is approximately of the order of one angstrom.

Accepted Answer

Introduction / Context: Orders of magnitude help engineers and scientists quickly estimate scales and choose appropriate measurement units. Atomic dimensions are central to discussions in chemistry, materials science, and nanotechnology. Given Data / Assumptions: The question asks for the typical size scale of an atom. We consider neutral atoms of common elements under standard conditions. No exact value is needed, only the correct order of magnitude. Concept / Approach: An angstrom (1 Å) equals 10^-10 metres, which is 10^-8 centimetres. Typical atomic diameters are on this order, though actual sizes vary with element and bonding context. A fermi (1 fm) equals 10^-15 metres (nuclear scale), a micron is 10^-6 metres (cellular/particulate scale), a millimetre is 10^-3 metres (macroscopic), and a nanometre is 10^-9 metres (often used for large molecules and small nanoparticles). While 1 nm = 10 Å, the canonical textbook order for atomic size is 1 Å. Step-by-Step Solution: List units with their magnitudes in metres.Relate atomic radius/diameter to these magnitudes.Recognize atoms have sizes near 1 Å, not fm, μm, mm, or even whole nanometres. Verification / Alternative check: Periodic trends and tabulated covalent/Van der Waals radii yield values close to fractions or multiples of an angstrom, confirming the order-of-magnitude choice. Why Other Options Are Wrong: Fermi: Nuclear dimensions (too small by ~10^5).Micron: Too large by ~10^4 compared to atoms.Millimetre: Macroscale, vastly larger.Nanometre: 1 nm = 10 Å; too large as the default order-of-magnitude benchmark for individual atoms. Common Pitfalls: Confusing nanometres (appropriate for small particles or large molecules) with angstroms (appropriate for atomic bond lengths and atomic radii). Final Answer: Angstrom (Å)

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