Deck 43: Energy From the Nucleus

Question 1

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

Answer 1

binding energy

Question 2

In a nuclear reactor the fissionable fuel is formed into pellets rather than finely ground and 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

Answer 2

non-fissioning absorption of neutrons

Question 3

The table lists properties of several heavy nuclei when they are struck by thermal neutrons; E_n is the excitation energy and E_b is the energy barrier. Which quantity, or combination of quantities, represents the energy put into the oscillation of the resulting compound nucleus?

A) E_n
B) E_b
C) E_n - E_b
D) E_b - E_n
E) Mass of the target nuclide + E_b

Answer 3

E_n

Question 4

Which one of the following is NOT needed in a nuclear fission reactor?

A) Moderator
B) Fuel
C) Coolant
D) Control device
E) Accelerator

Question 5

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

Question 6

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

Question 7

When fissions, the products might be:

A) , , and a proton
B) , , and a neutron
C) and
D) , , and an alpha particle
E) two uranium nuclei

Question 8

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 none of the above

Question 9

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

Question 10

The approximate amount of energy emitted in the fission of a nucleus such as ²³⁵U is:

A) 200 eV
B) 7.6 MeV
C) 200 MeV
D) 760 MeV
E) 200 GeV

Question 11

Consider the following energies: Rank them in order of increasing value.

A) 1, 2, 3, 4
B) 3, 4, 2, 1
C) 1, 2, 4, 3
D) 2, 1, 4, 3
E) 2, 4, 1, 3

Question 12

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

Question 13

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

Question 14

Which one of the following represents a fission reaction that can be activated by slow neutrons?

A) ²³⁸U₉₂ + ¹n₀ $\rightarrow$ ⁹⁰Kr₃₆ + ¹⁴⁶Cs₅₅ + ²H₁ + ¹n₀
B) ²³⁹Pu₉₄ + ¹n₀ $\rightarrow$ ⁹⁶Sr₃₈ + ¹⁴¹Ba₅₆ + 3¹n₀
C) ²³⁸U₉₂ $\rightarrow$ ²³⁴Th₉₀ + ⁴He₂
D) ³H₁ + ²H₁ $\rightarrow$ ⁴He₂ + ¹n₀
E) ¹⁰⁷Ag₄₇ + ¹n₀ $\rightarrow$ ¹⁰⁸Ag₄₇ $\rightarrow$ ¹⁰⁸Cd₄₈ + ⁰e_-1

Question 15

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

Question 16

Fission fragments usually decay by emitting:

A) alpha particles
B) electrons and neutrinos
C) positrons and neutrinos
D) only neutrons
E) only electrons

Question 17

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

Question 18

The binding energy per nucleon:

A) increases for all fission events
B) increases for some, but not all, fusion events
C) decreases for all fusion events
D) decreases for some, but not all, fission events
E) remains the same for all fusion events

Question 19

In the uranium disintegration series:

A) the emission of a $\beta$ ^- 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 $\alpha$ 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

Question 20

If the nucleus of a lead atom were broken into two identical nuclei, the total mass of the result would be:

A) the same as before
B) greater than before
C) less than before
D) converted into radiation
E) converted into kinetic energy

Question 21

Nuclear fusion in the Sun is increasing its supply of:

A) hydrogen
B) helium
C) nucleons
D) positrons
E) neutrons

Question 22

The overall proton-proton cycle is equivalent to:

A) 2¹H $\rightarrow$ ²H
B) 4¹H $\rightarrow$ ⁴H
C) 4¹H $\rightarrow$ ⁴H +4n
D) 4¹H + 2e^- $\rightarrow$ ⁴He + 2 $\nu$ + 6 $\gamma$
E) 4¹H + 2e⁺ $\rightarrow$ ⁴He + 2 $\nu$

Question 23

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

Question 24

The first step of the proton-proton cycle is:

A) ¹H + ¹H $\rightarrow$ ²H
B) ¹H + ¹H $\rightarrow$ ²H + e⁺ + $\nu$
C) ¹H + ¹H $\rightarrow$ ²H + e^- + $\nu$
D) ¹H + ¹H $\rightarrow$ ²H + $\gamma$
E) ¹H + ¹H $\rightarrow$ ³H + e^- + $\nu$

Question 25

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

Question 26

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

Question 27

Which one of the following represents a fusion reaction that would yield large amounts of energy?

A) ²³⁸U₉₂ + ¹n₀ $\rightarrow$ ⁹⁰Kr₃₆ + ¹⁴⁶Cs₅₅ + ²H₁ + ¹n₀
B) ²³⁹Pu₉₂ + ¹n₀ $\rightarrow$ ⁹⁶Sr₃₈ + ¹⁴¹Ba₅₆ + 3¹n₀
C) ²³⁸U₉₂ $\rightarrow$ ²³⁴Th₉₀ + ⁴He₂
D) ³H₁ + ²H₁ $\rightarrow$ ⁴He₂ + ¹n₀
E) ¹⁰⁷Ag₄₇ + ¹n₀ $\rightarrow$ ¹⁰⁸Ag₄₇ $\rightarrow$ ¹⁰⁸Cd₄₈ + ⁰e_-1

Question 28

The 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

Question 29

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) 1/4
B) 1/2
C) 1
D) 2
E) 4

Question 30

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

Question 31

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 fusion event produces fewer neutrons than when the reactor is critical
D) each fusion event produces more neutrons than when the reactor is critical
E) none of the above

Question 32

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

Question 33

Two billion years ago, a natural nuclear reactor formed in a uranium deposit in Africa. Why is it not possible for such a natural reactor to form somewhere on Earth today?

A) It is in fact possible for this to occur.
B) Too much uranium has already been mined for this to occur.
C) Too much ²³⁵U has now decayed for a critical mass to form naturally.
D) The remaining uranium deposits are too far underground for this to occur.
E) Uranium in the remaining deposits is mixed with too many other elements for this to occur.

Question 34

The Sun has enough hydrogen in its core to continue fusing hydrogen to helium for about another:

A) million years
B) five million years
C) five billion years
D) five trillion years
E) The Sun can continue to fuse hydrogen to helium indefinitely.

Question 35

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

Question 36

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

Question 37

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

Question 38

The binding energy per nucleon:

A) increases from 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

Question 39

What was the most convincing evidence that a natural nuclear reactor formed two billion years ago in a uranium deposit in Africa?

A) the relative depletion of ²³⁵U in the deposit
B) the relative depletion of ²³⁸U in the deposit
C) the relative abundance of lead in the deposit
D) the isotopic distribution of neodymium in the deposit
E) the appearance of radiation damage in the surrounding rock

Question 40

If a control rod is pulled rapidly out of a nuclear reactor core, what controls the response time (how fast the power level increases)?

A) the speed at which the rod can be removed
B) the speed at which neutrons are captured
C) the rate at which delayed neutrons from beta decay of fission fragments are emitted
D) the rate at which the coolant circulates in the core
E) the time between when a neutron is captured and when the nucleus actually fissions

Question 41

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)

Question 42

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) 20 s

Question 43

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

Question 44

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

Question 45

Nuclear fusion in stars produces all the chemical elements with mass numbers less than:

A) 56
B) 66
C) 70
D) 82
E) 92

Question 46

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

Question 47

Tokamaks confine deuteron plasmas using:

A) thick steel walls
B) magnetic fields
C) laser beams
D) vacuum tubes
E) electric fields

Question 48

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

Question 49

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

Question 50

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 = 0 K