IBPhysicsHLTopic QuestionsNuclear & Quantum PhysicsFission

Syllabus Edition

First teaching 2023

First exams 2025

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Fission (HL IB Physics)

Topic Questions

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1
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In a nuclear reactor, a chain reaction is produced and controlled. Uranium-235 is the isotope used in many nuclear reactors.

Which of the following statements about chain reactions is incorrect?

  • 2 or 3 neutrons are released every second.

  • Neutrons released from fission can trigger further fission reactions.

  • When neutrons are absorbed at the same rate they are produced, this leads to a chain reaction.

  • Neutrons released from fission can be absorbed by other uranium nuclei.

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2
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Nuclear reactions can be represented by equations.

straight U presubscript 92 presuperscript 235 plus straight n presubscript 0 presuperscript 1 rightwards arrow 2 space Pd presubscript 46 presuperscript 116 space plus 4 space straight n presubscript 0 presuperscript 1

Which type of reaction does the equation show?

  • Alpha decay

  • Beta decay

  • Nuclear fusion

  • Nuclear fission

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3
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Which statement about the moderator in a nuclear reactor is incorrect?

  • The purpose of a moderator is to slow down neutrons

  • The moderating material is usually fissionable 

  • The moderating material encourages further fission reactions with uranium fuel 

  • The moderator is usually water or graphite 

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4
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When uranium-235 undergoes fission in a nuclear reactor, about 180 MeV of energy is released.

In which form is this energy released?

  • potential energy

  • heat energy

  • electrical energy

  • nuclear energy

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5
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For a nuclear reactor in which the fission rate is constant, which of the following statements is correct? 

  • One neutron is released per fission reaction

  • There is a critical mass of fuel in the reactor

  • All neutrons remain in the reactor

  • For every fission reaction, there is, on average, one further fission reaction

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1
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Nuclear power stations use a fission reactor to create a nuclear reaction. A nucleus absorbs one neutron, leading to a reaction where more than one neutron is released. These neutrons in turn will set off more reactions in a process called a chain reaction.

Which one of these decay processes would be suitable to create a chain reaction?

  • B presubscript 5 presuperscript 10 space plus space n presubscript 0 presuperscript 1 space rightwards arrow space L presubscript 3 presuperscript 7 i space plus space.............

  • A presubscript 13 presuperscript 27 l space plus space a presubscript 2 presuperscript 4 space rightwards arrow space P presubscript 15 presuperscript 30 space plus space.............

  • P presubscript 15 presuperscript 30 rightwards arrow space S presubscript 14 presuperscript 30 i space plus space.............

  • U presubscript 92 presuperscript 235 space plus space n presubscript 0 presuperscript 1 space rightwards arrow space C presubscript 55 presuperscript 138 s space plus space R presubscript 37 presuperscript 95 b space plus space.............

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2
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A nuclear reaction is given below: 

            U presubscript 92 presuperscript 235 space plus n presubscript 0 presuperscript 1 space rightwards arrow space B presubscript 56 presuperscript 142 a space plus space K presubscript 36 presuperscript 91 r space plus 3 n presubscript 0 presuperscript 1 space plus 174.4 space M e V

You may use the following data:

  • Mass of U presubscript 92 presuperscript 235 = 235.0439 u
  • Mass of  B presubscript 56 presuperscript 142 a = 141.9164 u
  • Mass of K presubscript 36 presuperscript 91 r = 90.9234 u
  • 1 u = 931.5 MeV = 1.6610 × 10–27 kg 

From this data, the mass of a neutron can be inferred as which of the following?

  • 1.9921 × 10–27 kg

  • 1.9959 × 10–27 kg

  • 1.9770 × 10–27 kg

  • 1.9860 × 10–27 kg

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3
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Burning one metric tonne (1000 kg) of coal can yield 3.30 × 1010 J of energy, while the fission of a single uranium-235 nucleus yields, on average, a much larger amount of energy. 

When a thermal neutron is absorbed by a uranium-235 nucleus, it produces fission products as well as three neutrons, as given by the equation below: 

             n presubscript 0 presuperscript 1 space plus space U presubscript 92 presuperscript 235 space rightwards arrow Z presubscript 40 presuperscript 98 r space plus T presubscript 52 presuperscript 135 e space plus 3 n presubscript 0 presuperscript 1+ energy 

What is the mass of coal needed to give the same amount of energy as 1 kg of uranium-235? 

You may use the following data:

  • Mass of begin mathsize 20px style n presubscript 0 presuperscript 1 end style= 1.00866 u
  • Mass of  U presubscript 92 presuperscript 235= 235.0439 u
  • Total mass of  Z presubscript 40 presuperscript 98 r space plus space T presubscript 52 presuperscript 135 e  = 232.8292 u

  • 5.3 × 109 kg

  • 2.9 × 1010 kg

  • 7.6 × 1013 kg

  • 2.3 × 106 kg

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4
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Nucleus N1 undergoes a fission reaction into nucleus N2 which undergoes a further fission reaction into nucleus N3.

The binding energies per nucleon of the three nuclei are E1, E2 and E3 respectively.

Which of the following expressions is correct?

  • E subscript 1 space greater than space E subscript 2 and E subscript 3 space greater than space E subscript 2 space

  • E subscript 2 space greater than space E subscript 3 and E subscript 2 space greater than space E subscript 3 space

  • E subscript 1 space greater than space E subscript 2 and E subscript 1 space greater than space E subscript 3

  • E subscript 2 space greater than space E subscript 1 and E subscript 3 space greater than space E subscript 1

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5
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One possible fission reaction of uranium-235 following the capture of a thermal neutron is:

straight n presubscript 0 presuperscript 1 space plus space straight U presubscript 92 presuperscript 235 space rightwards arrow space open square brackets straight U presubscript 92 presuperscript 236 close square brackets space rightwards arrow space Zr presubscript 40 presuperscript 98 space plus space Te presubscript 52 presuperscript 136 space plus space 2 straight n presubscript 0 presuperscript 1 space plus space 206 space MeV

Which statement(s) about this reaction is/are correct?

  1. The binding energy of the U presubscript 92 presuperscript 236 nucleus is 206 MeV.
  2. The combined rest mass of the fission products equals the rest mass of the U presubscript 92 presuperscript 236 nucleus.
  3. The nucleon number is unchanged by the fission process.

 

  • I, II and III

  • I and II only

  • II and III only

  • III only

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1
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Which of the following isotopes releases the least amount of potential energy during nuclear fission?

  • Uranium-235

  • Thorium-231

  • Radon-222

  • Osmium-190

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2
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Which statement is correct regarding nuclear fission?

  • The daughter nucleus has a greater nucleon number than the original nucleus

  • Energy is absorbed during nuclear fission

  • The combined mass of the daughter nuclei is less than the mass of the original nucleus

  • Nuclear fission is the joining of two small nuclei to produce a larger nucleus

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Nuclear reactors use different substances for moderation and for control depending on their ability to absorb neutrons. Some information about commonly used substances:

  • Boron and cadmium are good absorbers of neutrons
  • Graphite and water are poor absorbers of neutrons

Using this information, which row shows the ideal substances that could be used for controlling and moderating in a nuclear reactor? 

 

Ideal controlling substance

Ideal moderating substance

A

boron

water

B

boron

cadmium

C

carbon

cadmium

D

carbon

water

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4
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Which statement about nuclear power is incorrect?

  • Concrete shielding is a preventative measure to ensure harmful radiation does not escape from a nuclear reactor

  • An advantage of nuclear power is that it produces no polluting gases 

  • The decay constant of high-level radioactive waste is extremely large 

  • Generating energy from nuclear processes is generally more efficient than generating energy from fossil fuels

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5
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In a nuclear reactor, a self-sustained chain reaction is possible because:

I.    More neutrons are released in each fission reaction.

II.   Every neutron released in a fission reaction immediately initiates a further fission reaction.

III.  The fast neutrons are slowed down by the moderator.

Which statements are correct?

  • I and II only

  • I and III only

  • II and III only

  • I, II and III

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