Chapter 25: Nuclear Physics and Particle Physics (Set-2)
Which quantity mainly explains nearly constant nuclear density across nuclei?
A Electron cloud
B Nuclear forces
C Coulomb force
D Atomic size
Nuclear forces are short-range and saturating, so each nucleon interacts only with nearby nucleons. This leads to almost constant density for all nuclei, irrespective of size.
Packing fraction of a nucleus is related to?
A Atomic radius
B Electron mass
C Mass defect
D Nuclear charge
Packing fraction is the mass defect per nucleon. It reflects how tightly nucleons are bound inside the nucleus and helps compare stability of different nuclei.
Which force mainly overcomes Coulomb repulsion inside nucleus?
A Nuclear force
B Weak force
C Gravitational
D Magnetic force
Strong nuclear force is attractive and much stronger than Coulomb repulsion at short distances, holding protons and neutrons together inside the nucleus.
Stability of heavy nuclei requires relatively more?
A Protons
B Electrons
C Neutrons
D Positrons
Extra neutrons reduce proton–proton repulsion without adding electric charge. Hence heavy stable nuclei lie above the N = Z line on stability curve.
Nuclear magnetic moment arises mainly due to?
A Electron motion
B Proton charge
C Nuclear radius
D Nucleon spin
Nuclear magnetic moment comes from intrinsic spin and orbital motion of protons and neutrons. Neutrons contribute despite being electrically neutral.
Which model explains nuclear deformation effects?
A Collective model
B Liquid drop model
C Shell model
D Atomic model
Collective model combines shell motion and collective vibrations or rotations, explaining deformation and energy levels of non-spherical nuclei.
Liquid drop model fails to explain?
A Nuclear fission
B Average binding energy
C Magic numbers
D Surface energy
Liquid drop model treats nucleus as uniform fluid and cannot explain extra stability of magic numbers, which is successfully explained by shell model.
Which term in mass formula accounts for neutron–proton imbalance?
A Coulomb term
B Asymmetry term
C Volume term
D Pairing term
Asymmetry term reduces binding energy when neutron and proton numbers differ greatly, reflecting Pauli exclusion principle effects inside nucleus.
Nuclear level scheme mainly shows?
A Energy states
B Electron shells
C Nuclear radius
D Decay constant
Nuclear level scheme represents discrete energy levels of nucleus, similar to atomic levels, helping understand gamma transitions and nuclear excitations.
Which decay occurs due to electromagnetic interaction?
A Alpha decay
B Beta decay
C Neutron decay
D Gamma decay
Gamma decay involves emission of high-energy photon when nucleus moves from excited state to lower energy state without changing A or Z.
Activity of radioactive sample depends directly on?
A Half-life only
B Nuclear radius
C Number of nuclei
D Electron shells
Activity equals decay constant times number of undecayed nuclei. More unstable nuclei present means more decays per second.
Beta decay energy spectrum is continuous because of?
A Neutrino emission
B Gamma emission
C Electron capture
D Nuclear recoil
In beta decay, energy is shared between electron and neutrino. This leads to continuous energy spectrum instead of discrete values.
Nuclear transmutation refers to?
A Chemical reaction
B Nuclear size change
C Electron exchange
D Element conversion
Nuclear transmutation means transformation of one element into another due to radioactive decay or nuclear reactions altering atomic number.
Which quantity remains conserved in all nuclear reactions?
A Rest mass
B Atomic radius
C Total energy
D Packing fraction
Total energy including rest-mass energy is always conserved in nuclear reactions, even though individual masses may change.
Resonance capture mainly involves?
A Fast neutrons
B Resonant energy neutrons
C Thermal neutrons
D Alpha particles
Resonance capture occurs when neutron energy matches specific nuclear energy levels, causing sharp increase in absorption probability.
Criticality in nuclear reactor refers to?
A Fuel temperature
B Radiation level
C Neutron balance
D Cooling rate
Reactor is critical when each fission produces exactly one neutron causing another fission, keeping power steady.
Ionization chamber differs from GM counter mainly by?
A Operating voltage
B Gas type
C Radiation type
D Detector shape
Ionization chambers work at lower voltages and collect ion pairs without multiplication, unlike GM counters which use avalanche multiplication.
Dead time of detector means?
A Time of decay
B Counting efficiency
C Exposure duration
D Recovery interval
Dead time is the short period after detecting radiation during which detector cannot record another event.
Linear accelerator accelerates particles using?
A Circular motion
B Magnetic fields only
C Electric fields
D Gravitational pull
Linear accelerators use oscillating electric fields along straight path to increase particle energy step by step.
Synchrotron differs from cyclotron because?
A Variable frequency
B Constant frequency
C No magnetic field
D No electric field
In synchrotron, magnetic field and frequency change with particle energy to maintain stable circular orbit at relativistic speeds.
Fermions are particles with spin?
A 0
B Half-integer
C 1
D Integer only
Fermions have half-integer spin like 1/2 or 3/2 and obey Pauli exclusion principle, including quarks and leptons.
Bosons generally act as?
A Matter particles
B Stable nuclei
C Antiparticles
D Force carriers
Bosons have integer spin and often mediate fundamental forces, such as photons, gluons, and weak bosons.
Antiparticle of electron is?
A Neutron
B Proton
C Positron
D Neutrino
Positron has same mass as electron but opposite charge and lepton number. Electron-positron annihilation produces gamma rays.
Neutrinos mainly interact via?
A Weak force
B Strong force
C Electromagnetic force
D Gravitational force
Neutrinos have no charge and extremely small mass, interacting only through weak interaction and gravity, making them hard to detect.
Conservation of parity holds in?
A Weak interaction
B Strong interaction
C Beta decay
D Neutrino decay
Parity is conserved in strong and electromagnetic interactions but violated in weak interactions such as beta decay.
CP symmetry combines which two symmetries?
A Parity and time
B Charge and time
C Charge and parity
D Spin and parity
CP symmetry involves simultaneous reversal of charge and spatial coordinates. Its violation is observed in some weak interaction processes.
Lepton number conservation helps explain?
A Alpha decay
B Nuclear fission
C Gamma emission
D Beta decay products
Lepton number conservation requires emission of neutrino or antineutrino in beta decay to balance lepton numbers.
Muon lepton number belongs to?
A Electron
B Tau
C Muon
D Proton
Muons and their neutrinos carry muon lepton number, conserved separately from electron lepton number in basic weak interactions.
Isospin treats proton and neutron as?
A Nucleon doublet
B Charge variants
C Different particles
D Independent particles
Isospin concept treats proton and neutron as two states of same nucleon, simplifying strong interaction description.
Isospin conservation is valid mainly for?
A Weak interaction
B Strong interaction
C Electromagnetic
D Gravitational
Isospin is conserved in strong interactions but can be violated in electromagnetic and weak interactions.
Strangeness quantum number was introduced to explain?
A Electron spin
B Nuclear radius
C Long particle lifetimes
D Beta decay law
Strange particles are produced strongly but decay weakly. Strangeness conservation in strong interactions explains their unusual behavior.
Weak decay can change strangeness by?
A ±1
B Zero only
C ±2
D Any value
Weak interaction allows change in strangeness by one unit, unlike strong interaction where strangeness is conserved.
Hypercharge in Gell-Mann–Nishijima formula includes?
A Electric charge
B Baryon number
C Isospin
D Mass number
Hypercharge combines baryon number and strangeness, helping relate electric charge with isospin projection.