Multiple Choice Question (MCQs) is a process that tests student’s knowledge about comprehensive content and objectives and gives an insight into student ability.
- If the nucleus of a lead atom were broken into two identical nuclei, the total mass of the
resultant nuclei would be:
A. the same as before
B. greater than before
C. less than before
D. converted into radiation
E. converted into kinetic energy
Ans: C - Consider the following energies: 1.) minimum energy needed to excite a hydrogen atom2.) energy needed to ionize a hydrogen atom 3.) energy released in 235U fission 4. ) energy needed to remove a neutron from a 12C nucleus
Rank them in order of increasing value.
A. 1, 2, 3, 4
B. 1, 3, 2, 4
C. 1, 2, 4, 3
D. 2, 1, 4, 3
E. 2, 4, 1, 3
ans: C - The binding energy per nucleon:
A. increases for all fission events
B. increases for some, but not all, fission events
C. decreases for all fission events
D. decreases for some, but not all, fission events
E. remains the same for all fission events
ans: A - When uranium undergoes fission as a result of neutron bombardment, the energy released is
due to:
A. oxidation of the uranium
B. kinetic energy of the bombarding neutrons
C. radioactivity of the uranium nucleus
D. radioactivity of the fission products
E. a reduction in binding energy
ans: E
Chapter 43: ENERGY FROM THE NUCLEUS 637 - The energy supplied by a thermal neutron in a fission event is essentially its:
A. excitation energy
B. binding energy
C. kinetic energy
D. rest energy
E. electric potential energy
ans: B - The barrier to fission comes about because the fragments:
A. attract each other via the strong nuclear force
B. repel each other electrically
C. produce magnetic fields
D. have large masses
E. attract electrons electrically
ans: A - 235U is readily made fissionable by a thermal neutron but 238U is not because:
A. the neutron has a smaller binding energy in 236U
B. the neutron has a smaller excitation energy in 236U
C. the potential barrier for the fragments is less in 239U
D. the neutron binding energy is greater than the barrier height for 236U and less than the
barrier height for 239U
E. the neutron binding energy is less than the barrier height for 236U and greater than the
barrier height for 239U
ans: D - An explosion does not result from a small piece of 235U because:
A. it does not fission
B. the neutrons released move too fast
C. 238U is required
D. too many neutrons escape, preventing a chain reaction from starting
E. a few neutrons must be injected to start the chain reaction
ans: D - When 236U fissions the fragments are:
A. always 140Xe and 94Sr
B. always identical
C. never 140Xe and 94Sr
D. never identical
E. none of the above
ans: E
638 Chapter 43: ENERGY FROM THE NUCLEUS - Fission fragments usually decay by emitting:
A. alpha particles
B. electrons and neutrinos
C. positrons and neutrinos
D. only neutrons
E. only electrons
ans: B - When 236U fissions, the products might be:
A. 146Ba, 89Kr, and a proton
B. 146Ba, 89Kr, and a neutron
C. 148Cs and 85Br
D. 133I, 92Sr, and an alpha particle
E. two uranium nuclei
ans: B - Consider all possible fission events. Which of the following statements is true?
A. Light initial fragments have more protons than neutrons and heavy initial fragments have
fewer protons than neutrons
B. Heavy initial fragments have more protons than neutrons and light initial fragments have
fewer protons than neutrons
C. All initial fragments have more protons than neutrons
D. All initial fragments have about the same number of protons and neutrons
E. All initial fragments have more neutrons than protons
ans: E - Which one of the following represents a fission reaction that can be activated by slow neutrons?
A. 238U92 + 1n0 → 90Kr36 + 146Cs55 + 2H1 + 1n0
B. 239Pu94 + 1n0 → 96Sr38 + 141Ba56 + 3 1n0
C. 238U92 → 234Th90 + 4He2
D. 3H1 + 2H1 → 4He2 + 1n0
E. 107Ag47 + 1n0 → 108Ag47 → 108Cd48 + 0e−1
ans: B - In the uranium disintegration series:
A. the emission of a β− particle increases the mass number A by one and decreases the atomic
number Z by one
B. the disintegrating element merely ejects atomic electrons
C. the emission of an α particle decreases the mass number A by four and decreases the atomic
number Z by two
D. the nucleus always remains unaffected
E. the series of disintegrations continues until an element having eight outermost orbital electrons is obtained
ans: C
Chapter 43: ENERGY FROM THE NUCLEUS 639 - Separation of the isotopes of uranium requires a physical, rather than chemical, method because:
A. mixing other chemicals with uranium is too dangerous
B. the isotopes are chemically the same
C. the isotopes have exactly the same number of neutrons per nucleus
D. natural uranium contains only 0.7% 235U
E. uranium is the heaviest element in nature
ans: B - Which one of the following is NOT needed in a nuclear fission reactor?
A. Moderator
B. Fuel
C. Coolant
D. Control device
E. Accelerator
ans: E - The function of the control rods in a nuclear reactor is to:
A. increase fission by slowing down the neutrons
B. decrease the energy of the neutrons without absorbing them
C. increase the ability of the neutrons to cause fission
D. decrease fission by absorbing neutrons
E. provide the critical mass for the fission reaction
ans: D - A nuclear reactor is operating at a certain power level, with its multiplication factor adjusted
to unity. The control rods are now used to reduce the power output to one-half its former
value. After the reduction in power the multiplication factor is maintained at:
A. 1/2
B. 1/4
C. 2
D. 4
E. 1
ans: E - The purpose of a moderator in a nuclear reactor is to:
A. provide neutrons for the fission process
B. slow down fast neutrons to increase the probability of capture by uranium
C. absorb dangerous gamma radiation
D. shield the reactor operator from dangerous radiation
E. none of the above
ans: B
640 Chapter 43: ENERGY FROM THE NUCLEUS - In a neutron-induced fission process, delayed neutrons come from:
A. the fission products
B. the original nucleus just before it absorbs the neutron
C. the original nucleus just after it absorbs the neutron
D. the moderator material
E. the control rods
ans: A - In a nuclear reactor the fissionable fuel is formed into pellets rather than finely ground and the
pellets are mixed with the moderator. This reduces the probability of:
A. non-fissioning absorption of neutrons
B. loss of neutrons through the reactor container
C. absorption of two neutrons by single fissionable nucleus
D. loss of neutrons in the control rods
E. none of the above
ans: A - In a subcritical nuclear reactor:
A. the number of fission events per unit time decreases with time
B. the number of fission events per unit time increases with time
C. each fission event produces fewer neutrons than when the reactor is critical
D. each fission event produces more neutrons than when the reactor is critical
E. none of the above
ans: A - In the normal operation of a nuclear reactor:
A. control rods are adjusted so the reactor is subcritical
B. control rods are adjusted so the reactor is critical
C. the moderating fluid is drained
D. the moderating fluid is continually recycled
E. none of the above
ans: B - In a nuclear power plant, the power discharged to the environment:
A. can be made zero by proper design
B. must be less than the electrical power generated
C. must be greater than the electrical power generated
D. can be entirely recycled to produce an equal amount of electrical power
E. is not any of the above
ans: E
Chapter 43: ENERGY FROM THE NUCLEUS 641 - The binding energy per nucleon:
A. increases for all fusion events
B. increases for some, but not all, fusion events
C. remains the same for some fusion events
D. decreases for all fusion events
E. decreases for some, but not all, fusion events
ans: A - To produce energy by fusion of two nuclei, the nuclei must:
A. have at least several thousand electron volts of kinetic energy
B. both be above iron in mass number
C. have more neutrons than protons
D. be unstable
E. be magic number nuclei
ans: A - Which one of the following represents a fusion reaction that yields large amounts of energy?
A. 238U92 + 1n0 → 90Kr36 + 146Cs55 + 2H1 + 1n0
B. 239Pu92 + 1n0 → 96Sr38 + 141Ba56 + 31n0
C. 238U92 → 234Th90 + 4He2
D. 3H1 + 2H1 → 4He2 + 1n0
E. 107Ag47 + 1n0 → 108Ag47 → 108Cd48 + 0e−1
ans: D - The barrier to fusion comes about because protons:
A. attract each other via the strong nuclear force
B. repel each other electrically
C. produce magnetic fields
D. attract neutrons via the strong nuclear force
E. attract electrons electrically
ans: B - High temperatures are required in thermonuclear fusion so that:
A. some nuclei are moving fast enough to overcome the barrier to fusion
B. there is a high probability some nuclei will strike each other head on
C. the atoms are ionized
D. thermal expansion gives the nuclei more room
E. the uncertainty principle can be circumvented
ans: A - For a controlled nuclear fusion reaction, one needs:
A. high number density n and high temperature T
B. high number density n and low temperature T
C. low number density n and high temperature T
D. low number density n and low temperature T
E. high number density n and temperature T = 0K
ans: A
642 Chapter 43: ENERGY FROM THE NUCLEUS - Most of the energy produced by the Sun is due to:
A. nuclear fission
B. nuclear fusion
C. chemical reaction
D. gravitational collapse
E. induced emfs associated with the Sun’s magnetic field
ans: B - Nuclear fusion in stars produces all the chemical elements with mass numbers less than:
A. 56
B. 66
C. 70
D. 82
E. 92
ans: A - Nuclear fusion in the Sun is increasing its supply of:
A. hydrogen
B. helium
C. nucleons
D. positrons
E. neutrons
ans: B - Which of the following chemical elements is not produced by thermonuclear fusion in stars?
A. Carbon (Z = 6, A ≈ 12)
B. Silicon (Z = 14, A ≈ 28)
C. Oxygen (Z = 8, A ≈ 16)
D. Mercury (Z = 80, A ≈ 200)
E. Chromium (Z = 24, A ≈ 52)
ans: D - The first step of the proton-proton cycle is:
A. 1H + 1H → 2H
B. 1H + 1H → 2H + e+ + ν
C. 1H + 1H → 2H + e− + ν
D. 1H + 1H → 2H + γ
E. 1H + 1H → 3H + e− + ν
ans: B - The overall proton-proton cycle is equivalent to:
A. 2 1H → 2H
B. 4 1H → 4H
C. 4 1H → 4H + 4n
D. 4 1H+2e− → 4He + 2ν + 6γ
E. 4 1H+2e+ → 4He + 2ν + 3γ
ans: D
Chapter 43: ENERGY FROM THE NUCLEUS 643The energy released in a complete proton-proton cycle is about: - A. 3 keV
B. 30 keV
C. 3 MeV
D. 30 MeV
E. 300 MeV
ans: D - For purposes of a practical (energy producing) reaction one wants a disintegration energy Q
that is:
A. positive for fusion reactions and negative for fission reactions
B. negative for fusion reactions and positive for fission reactions
C. negative for both fusion and fission reactions
D. positive for both fusion and fission reactions
E. as close to zero as possible for both fusion and fission reactions
ans: D - Lawson’s number is 1020 s · m−3. If the density of deuteron nuclei is 2 × 1021 m−3 what should
the confinement time be to achieve sustained fusion?
A. 16 ms
B. 50 ms
C. 160 ms
D. 250 ms
E. 500 ms
ans: B - Tokamaks confine deuteron plasmas using:
A. thick steel walls
B. magnetic fields
C. laser beams
D. vacuum tubes
E. electric fields
ans: B - Most magnetic confinement projects attempt:
A. proton-proton fusion
B. proton-deuteron fusion
C. deuteron-deuteron fusion
D. deuteron-triton fusion
E. triton-triton fusion
ans: C
644 Chapter 43: ENERGY FROM THE NUCLEUS - Compared to fusion in a tokamak, laser fusion makes use of:
A. smaller particle number densities
B. greater particle number densities
C. longer confinement times
D. higher temperatures
E. lower temperatures
ans: B - Most laser fusion projects attempt:
A. proton-proton fusion
B. proton-deuteron fusion
C. deuteron-deuteron fusion
D. deuteron-triton fusion
E. triton-triton fusion
ans: D - In laser fusion, the laser light is:
A. emitted by the reacting nuclei
B. used to cause transitions between nuclear energy levels
C. used to cause transitions between atomic energy levels
D. used to replace the emitted gamma rays
E. used to heat the fuel pellet
ans: E