83 practice questions on Nuclei , sorted Easy → Hard. Try each one first, then open its answer page for the worked explanation. Want the full theory first? Read the Nuclei notes .
Binding Energy per Nucleon vs Mass Number Mass number A BE/nucleon Fe-56 (peak, most stable) FUSION region (light → medium) FISSION region (heavy → medium) Both processes release energy by moving nuclei toward the Fe-56 peak Binding energy per nucleon rises sharply for light nuclei, peaks around iron-56 (the most stable nucleus), then slowly declines for heavier nuclei - which is exactly why fusing light nuclei or splitting heavy nuclei both release energy: each moves the products toward this stability peak.
Easy - 25 questions Q1.
The number of neutrons N in a nucleus of mass number A and atomic number Z is:
A A − ZB A + ZC 2Z − AD A × ZShow answer & explanation →
Q3.
Which particle has nearly the same mass as a proton but carries no charge?
A electronB positronC neutronD photonShow answer & explanation →
Q4.
One fermi, the convenient unit for nuclear sizes, equals:
A 10<sup>-9</sup> mB 10<sup>-12</sup> mC 10<sup>-10</sup> mD 10<sup>-15</sup> mShow answer & explanation →
Q5.
Isobars are nuclei that have the same:
A mass numberB atomic numberC number of neutronsD number of electronsShow answer & explanation →
Q6.
The nucleus of an atom consists of:
A Mainly protonsB Mainly neutronsC Protons and neutronsD Electrons and protonsShow answer & explanation →
Q7.
Atomic number Z of an element is:
A Number of neutronsB Number of protonsC Mass numberD Number of electrons in outer shellShow answer & explanation →
Q8.
Alpha radiation consists of:
A Electrons ejected directly from the nucleusB Helium-4 nuclei (2 protons + 2 neutrons)C High energy photons emitted from nuclear transitionsD Free neutrons ejected from an unstable nucleusShow answer & explanation →
Q9.
Beta-minus decay involves:
A Emission of a helium nucleus consisting of two protons and two neutronsB Emission of an electron from nucleus (neutron to proton)C Emission of a high-energy photon from a nuclear energy transitionD Absorption of a neutron by the nucleus from outsideShow answer & explanation →
Q10.
Gamma rays are:
A Protons emitted from nucleus under typical conditionsB Electrons from nucleus according to standard textbooksC High energy electromagnetic radiationD Neutrons in general practice as frequently describedShow answer & explanation →
Q11.
Half-life of a radioactive element is the time for:
A All atoms to decayB Half the sample to decayC Sample to reach normal temperatureD Radiation to decrease to zeroShow answer & explanation →
Q14.
Nuclear fission is:
A Fusion of light nucleiB Splitting of heavy nucleusC Radioactive decayD Beta emissionShow answer & explanation →
Q15.
Nuclear fusion is:
A Splitting of heavy nucleus in most textbook accountsB Joining of light nuclei releasing energyC Radioactive decay during normal conditionsD Alpha emission as generally observedShow answer & explanation →
Q16.
1 atomic mass unit (1 amu) in energy equivalent (Einstein mass-energy):
A 1 MeVB 931.5 MeVC 9.31 eVD 1 GeVShow answer & explanation →
Q18.
Mass defect in a nucleus is:
A Difference between mass of nucleus and sum of its nucleonsB The total mass of all orbital electrons around the nucleusC The combined mass of neutrons only, ignoring the protonsD The ratio of total nuclear charge to total nuclear massShow answer & explanation →
Q19.
Isotopes have the same:
A Mass number, which actually differs between isotopesB Number of neutrons, which actually differs between isotopesC Number of protons (atomic number)D Mass number, neutron number, and proton number all at onceShow answer & explanation →
Q20.
Carbon-14 dating is used to determine:
A Temperature of ancient samplesB Age of ancient organic materialsC Chemical compositionD Magnetic field of ancient objectsShow answer & explanation →
Q21.
Radioactive decay constant lambda is related to half-life by:
A lambda = ln2 x T(1/2)B lambda = ln2 / T(1/2)C lambda = T(1/2)/ln2D lambda = 1/T(1/2)Show answer & explanation →
Q22.
A nuclear chain reaction in fission occurs when:
A Average number of neutrons causing further fission > 1B Less than one neutron on average causes further fissionC The fuel temperature exceeds 10<sup>8</sup> K, as needed for fusionD All released neutrons are absorbed without causing fissionShow answer & explanation →
Q23.
Moderator in a nuclear reactor is used to:
A Slow down neutrons (for thermal fission)B Speed up and accelerate fission neutrons to higher energyC Absorb gamma rays emitted during the fission processD Generate electricity directly from the heat producedShow answer & explanation →
Q25.
The strong nuclear force:
A Acts over long range in typical laboratory settingsB Is repulsive between protons under usual circumstancesC Is strongest at short range inside nucleusD Is weaker than gravity according to most researchersShow answer & explanation →
Medium - 25 questions Q26.
The activity of a radioactive sample falls to one-eighth of its initial value in 15 days. Its half-life is:
A 3 daysB 5 daysC 7.5 daysD 15 daysShow answer & explanation →
Q28.
The mass defect in forming a deuteron from a free proton and neutron is 0.00239 u (1 u = 931.5 MeV). Its binding energy is:
A 8.8 MeVB 4.4 MeVC 1.1 MeVD 2.22 MeVShow answer & explanation →
Q29.
A radioactive nuclide has a half-life of 10 years. Its mean (average) life is:
A 14.4 yearsB 6.93 yearsC 10 yearsD 20 yearsShow answer & explanation →
Q31.
In a nuclear reaction, which of these is NOT conserved?
A Mass numberB ChargeC Kinetic energyD Mass-energy (total)Show answer & explanation →
Q32.
The Q-value of a nuclear reaction is:
A The total kinetic energy carried by the reactants before collisionB Energy released (or absorbed): Q = (mass_reactants - mass_products) × c²C The half-life of the radioactive product nucleus formedD The activity (decay rate) of the resulting product nucleusShow answer & explanation →
Q34.
Carbon-14 dating uses the decay: ¹⁴C → ¹⁴N + ?
A An alpha particle, which would instead reduce the mass number by fourB A gamma ray photon with no accompanying particle emissionC Beta minus particle (electron)D A free proton ejected directly from the nucleusShow answer & explanation →
Q35.
Radioactive decay law: N(t) = N₀ e<sup>-lambda t</sup>. Activity A = dN/dt in magnitude is:
A lambda N(t)B lambda/N(t)C N(t)/lambdaD lambda²N(t)Show answer & explanation →
Q37.
Nuclear fission of U-235 releases energy by:
A Converting protons directly into neutrons within the nucleusB Converting mass to energy via E=mc² (mass defect)C Beta emission alone, with no associated mass-energy conversionD Fusion of lighter nuclei into a single heavier nucleusShow answer & explanation →
Q38.
The moderator in a nuclear reactor:
A Absorbs neutrons permanently, removing them from the reactionB Slows down (moderates) fast neutrons to thermal energiesC Controls the overall reaction rate by being inserted or withdrawnD Cools the reactor core by directly carrying away heatShow answer & explanation →
Q39.
Critical mass in nuclear weapons/reactors refers to:
A Minimum mass for sustained chain reactionB The total mass of the entire reactor core including shieldingC The maximum mass legally permitted to be stored at one siteD Exactly half the total mass of fissile material availableShow answer & explanation →
Q40.
Gamma radiation is best shielded by:
A A sheet of paper, sufficient mainly for stopping alpha particlesB A thin sheet of aluminum, sufficient mainly for stopping beta particlesC Lead or concrete (dense material)D A thick layer of ordinary air at atmospheric pressureShow answer & explanation →
Q41.
Stable nuclei have mass number A such that:
A Z = A/2 exactly for every stable nucleus regardless of sizeB Z is approximately A/2 for light nuclei, Z < A/2 for heavy nucleiC The proton number Z is usually greater than the neutron number ND The neutron number N is usually exactly zero as frequently observed in practiceShow answer & explanation →
Q42.
The decay constant lambda and half-life T<sub>1</sub>/2 are related by:
A lambda = T<sub>1</sub>/2 / ln 2B lambda = ln 2 / T<sub>1</sub>/2C lambda = T<sub>1</sub>/2 × ln 2D lambda = 1 / T<sub>1</sub>/2Show answer & explanation →
Q43.
Neutrinos are emitted in:
A Alpha decay, which emits mainly a helium-4 nucleusB Gamma decay, which emits mainly a high-energy photonC Beta decay (along with electron/positron)D Fission mainly, and rarely in any other type of nuclear decayShow answer & explanation →
Q45.
Specific activity refers to:
A Number of nucleiB Activity per unit massC Total energy releasedD Half-life per gramShow answer & explanation →
Q47.
In a chain reaction, the multiplication factor k represents:
A Number of neutrons per fission as frequently describedB Ratio of neutrons in successive generationsC Total energy per fission in most textbook accountsD Control rod position during normal conditionsShow answer & explanation →
Q49.
The mass defect of a nucleus is:
A Mass of nucleus - sum of component nucleon massesB Usually exactly zero for any stable or unstable nucleusC Usually negative in magnitude for every known nucleusD The mass of the constituent protons mainly, ignoring neutronsShow answer & explanation →
Q50.
Radioactive dating works because:
A The decay constant of the isotope changes predictably over time as generally observedB The initial amount of radioactive isotope is assumed known and decay is predictableC The daughter products formed gradually disappear from the sample in typical laboratory settingsD All radioactive isotopes decay at exactly the same fixed rate under usual circumstancesShow answer & explanation →
Hard - 33 questions Q51.
The nucleus <sup>4</sup>He has a mass defect of 0.0304 u (1 u = 931.5 MeV). Its binding energy per nucleon is about:
A 28.3 MeVB 4.7 MeVC 7.1 MeVD 8.8 MeVShow answer & explanation →
Q52.
In the fusion reaction <sup>2</sup>H + <sup>3</sup>H → <sup>4</sup>He + n, the energy released is about:
A 3.2 MeVB 200 MeVC 11.9 MeVD 17.6 MeVShow answer & explanation →
Q53.
A radioactive sample has a half-life of 20 minutes. The fraction of the sample that decays in 1 hour is:
Show answer & explanation →
Q54.
The approximate energy released in a single fission of a <sup>235</sup>U nucleus is:
A 1.6 MeVB 200 MeVC 931 MeVD 8 MeVShow answer & explanation →
Q55.
A radioactive source has an initial activity of 6.4 × 10<sup>4</sup> Bq and a half-life of 3 hours. Its activity after 9 hours is:
A 3.2×10<sup>4</sup> BqB 1.6×10<sup>4</sup> BqC 8×10<sup>3</sup> BqD 2×10<sup>4</sup> BqShow answer & explanation →
Q56.
The binding energy of Fe-56 is approximately 492 MeV. Binding energy per nucleon:
A 8.79 MeV/nucleonB 5.6 MeV/nucleonC 14 MeV/nucleonD 56 MeV/nucleonShow answer & explanation →
Q57.
The semi-empirical mass formula (Bethe-Weizsacker) has terms for:
A Volume, surface, Coulomb, asymmetry, and pairingB Mainly the volume term and the surface term, with nothing elseC Mainly the Coulomb repulsion term, with little other contributionsD Just a single overall binding energy term with little further structureShow answer & explanation →
Q58.
Tunneling in alpha decay: the alpha particle tunnels through:
A The nucleus itself, as though it tunneled through its own point of originB The Coulomb barrier surrounding the nucleusC The surrounding electron cloud orbiting around the parent atomD A magnetic confinement barrier generated by the nuclear spinShow answer & explanation →
Q59.
Geiger-Nuttall law for alpha decay relates log(decay constant) to:
A The absolute temperature of the decaying sampleB 1/sqrt(Q) (inverse square root of Q-value)C The mass number A of the parent nucleus aloneD The atomic number Z of the parent nucleus squaredShow answer & explanation →
Q60.
The strong nuclear force acts:
A Between protons only, with no effect on neutrons at allB At long range, extending across the entire size of an atomC At short range (< 2-3 fm), between any nucleonsD Between nucleons and electrons, mediating their mutual attractionShow answer & explanation →
Q61.
Beta-minus decay: n → p + e⁻ + antineutrino. The antineutrino is needed for:
A Charge conservation, which is already satisfied by the electron aloneB Conservation of total rest mass before and after the decayC Energy and momentum conservation (and lepton number)D Baryon number conservation, which is unaffected by lepton emissionShow answer & explanation →
Q62.
In nuclear reactions using liquid drop model, fission occurs when:
A A < 50, a mass number range where stable light nuclei are commonB Electrostatic energy exceeds surface energy (fissility parameter x > 1 approx)C A = 56, the mass number of the most stable nucleus, iron-56D Temperature exceeds 10⁹ K, a condition relevant to stellar fusion insteadShow answer & explanation →
Q63.
Magic numbers (2, 8, 20, 28, 50, 82, 126) in nuclear physics indicate:
A Isotopes with equal protons and neutrons according to standard textbooksB Nuclei with closed shell structure (extra stability)C Number of isotopes in general practice as frequently describedD Decay products in most textbook accounts during normal conditionsShow answer & explanation →
Q64.
The pion (pi meson) is the particle primarily responsible for:
A Mediating the weak interaction responsible for beta decayB Mediating the nuclear force (residual strong force)C Mediating the electron capture process within the nucleusD Causing spontaneous radioactivity in unstable nuclei generallyShow answer & explanation →
Q65.
Nuclear fission vs fusion: which releases more energy per unit mass?
A FissionB FusionC EqualD Depends on temperatureShow answer & explanation →
Q66.
Radioactive equilibrium (secular) occurs when:
A The decay constants of parent and daughter are exactly equalB Daughter activity equals parent activity (after many daughter half-lives)C The half-lives of the parent and daughter nuclei are exactly equalD The total measured activity of the sample falls to zeroShow answer & explanation →
Q67.
The electron capture process is:
A An electron being emitted directly from inside the nucleusB Atomic electron absorbed by nucleus (p + e⁻ → n + neutrino)C A positron being emitted from the nucleus instead of absorbedD A gamma ray photon emitted following nuclear excitationShow answer & explanation →
Q68.
In a nuclear reactor, the four-factor formula k∞ =
A eta × epsilon × p × fB A × B × C × D as generally observedC n × p × f × e in typical laboratory settingsD power × time under usual circumstancesShow answer & explanation →
Q69.
The thermonuclear reaction in stars: Proton-proton chain. Net reaction:
A 4H → He-4 + energyB 4H → He-3 + energyC 2H → H-2 + energyD H → n + eShow answer & explanation →
Q70.
Spent nuclear fuel is primarily radioactive due to:
A The small amount of unfissioned U-235 remaining in the fuel rodsB Fission products (including long-lived isotopes) and actinidesC The cooling water that circulates through the reactor coreD The structural metal materials used to build the fuel assemblyShow answer & explanation →
Q71.
The cross-section sigma in nuclear reactions measures:
A The literal physical geometric size of the target nucleusB Effective target area for reaction probability (in barns = 10⁻²⁴ cm²)C The kinetic energy carried by the incoming projectile particleD The mass defect of the nucleus formed after the reactionShow answer & explanation →
Q72.
Isomers in nuclear physics are nuclei with:
A Same A and Z but different binding energy, with no excited-state distinctionB Same A and Z but different energy states (metastable excited states)C Different Z but same A, which instead describes isobarsD Different A but same Z, which instead describes isotopesShow answer & explanation →
Q73.
Pair production (photon → e⁺ + e⁻) requires photon energy greater than:
A 0.511 MeVB 1.022 MeVC 2.044 MeVD 0.511 keVShow answer & explanation →
Q74.
Annihilation radiation: when e⁺ and e⁻ annihilate, they produce:
A One single gamma photon carrying 1.022 MeV in one directionB Two gammas, each 0.511 MeV emitted in opposite directionsC A single alpha particle ejected from the annihilation pointD A pair of neutrinos with no accompanying photon emissionShow answer & explanation →
Q75.
The Breit-Wigner resonance formula describes nuclear cross-section as a function of energy near:
A Mainly the reaction threshold energy, with little peak elsewhereB A resonance energy (sharp peak in cross-section)C All energies uniformly, with a perfectly flat cross-section curveD Mainly thermal neutron energies, with little dependence elsewhereShow answer & explanation →
Q76.
The radius of a nucleus is proportional to A<sup>1/3</sup>. If the mass number increases eightfold, the nuclear radius becomes:
Show answer & explanation →
Q77.
A nuclear reaction has a mass defect of 0.1 u (1 u = 931.5 MeV). The energy released is:
A 9.3 MeVB 93.15 MeVC 931.5 MeVD 1862 MeVShow answer & explanation →
Q79.
In beta-minus decay, the atomic number of the nucleus:
A increases by 1B decreases by 1C remains unchangedD increases by 2Show answer & explanation →
Q80.
When a nucleus undergoes alpha decay, its mass number and atomic number change by:
A A − 4 and Z − 2B A − 2 and Z − 4C A − 4 and Z − 1D A and Z − 2Show answer & explanation →
Q82.
A radioactive sample of 800 atoms has a half-life of 5 years. The number of atoms remaining after 15 years is:
Show answer & explanation →
Q83.
The density of nuclear matter is:
A approximately independent of mass numberB proportional to AC proportional to A²D proportional to 1/AShow answer & explanation →