What does Fission cover in IB Physics?

This topic explores nuclear fission, focusing on how energy is released and harnessed. Understand energy release in spontaneous and neutron-induced fission. Know the role of chain reactions in nuclear fission reactors.

Both. SL and HL students study Fission to the same depth.

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FourtyFive has 21 Fission questions. Every answer you write is marked mark by mark, IB-style, and you see where each mark was won or lost. Every part has a hint, the AI tutor helps you through the step you are stuck on, and your Study Profile picks what to practise next.

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Topic E.4 · SL and HL

Fission: notes and practice questions

Q: How do I revise Fission for IB Physics?

Start from the core idea: this topic explores nuclear fission, focusing on how energy is released and harnessed. In the exam: both papers, both levels, and small: 4 hours of teaching. The two shapes are a mass-defect energy calculation from supplied nuclide masses, and a describe or outline of what a moderator or control rod does. Then practise exam-style questions, easiest first, writing out every step of your working before you check it.

10 min read Jump to 20 practice questions

Summary

This topic explores nuclear fission, focusing on how energy is released and harnessed.
Understand energy release in spontaneous and neutron-induced fission.
Know the role of chain reactions in nuclear fission reactors.
Identify the functions of control rods, moderators, heat exchangers, and shielding in nuclear power plants.
Describe the properties and management of nuclear fission products.
Perform calculations to determine the energy released in fission reactions.
Consider the impact of long-term storage of nuclear waste.

How it is examined

Both papers, both levels, and small: 4 hours of teaching. The two shapes are a mass-defect energy calculation from supplied nuclide masses, and a describe or outline of what a moderator or control rod does. This is one of the few places in the syllabus where a well-formed question can be almost pure AO1 recall.

Key ideas

that energy is released in spontaneous and neutron-induced fission
the role of chain reactions in nuclear fission reactions
the role of control rods, moderators, heat exchangers and shielding in a nuclear power plant
the properties of the products of nuclear fission and their management

Guiding questions

In which form is energy stored within the nucleus of the atom?
How can the energy released from the nucleus be harnessed?

Linking questions

In which form is energy released as a result of nuclear fission?
How is binding energy used to determine the rate of energy production in a nuclear power plant?
To what extent is there a role for fission in addressing climate change? (NOS)

Practice questions

21 questions · 10 easy · 9 medium · 2 hard

Showing 20 of 20

Question 1

EasyPaper 1A · calculator1 mark

What is the primary function of the moderator in a thermal nuclear fission reactor?

A. To absorb excess neutrons to control the rate of the chain reaction.

B. To reduce the kinetic energy of fast neutrons.

C. To transfer thermal energy from the reactor core to the heat exchanger.

D. To provide shielding against ionizing radiation.

Question 2

MediumPaper 1A · calculator1 mark

In a conceptual model of a fusion-fission hybrid reactor, an average of five neutrons are produced for every fission event.

The average number of neutrons absorbed by a surrounding lithium blanket to breed tritium is $N_T$ per fission.

The average number of neutrons that escape the reaction chamber is $N_E$ per fission.

The remaining neutrons are available to induce further fission events.

What are possible values for $N_T$ and $N_E$ for the reactor to operate in a critical state?

	$N_T$	$N_E$
A.	1	2
B.	2	2
C.	3	2
D.	2	1

Question 3

HardPaper 2 · calculator16 marks

(a)

A prototype nuclear reactor uses Plutonium-239 ( $_{94}^{239}\text{Pu}$ ) as fuel. When a neutron is captured by a Plutonium-239 nucleus, one of two possible fission reactions can occur.

Reaction 1: $\text{n} + _{94}^{239}\text{Pu} \rightarrow _{54}^{134}\text{Xe} + _{40}^{103}\text{Zr} + 3\text{n}$

Reaction 2: $\text{n} + _{94}^{239}\text{Pu} \rightarrow _{58}^{144}\text{Ce} + _{36}^{94}\text{Kr} + 2\text{n}$

The following data are available:

Nuclide/Particle	Mass / u
Plutonium-239 ( $_{94}^{239}\text{Pu}$ )	239.05216
Xenon-134 ( $_{54}^{134}\text{Xe}$ )	133.90539
Zirconium-103 ( $_{40}^{103}\text{Zr}$ )	102.92658
Cerium-144 ( $_{58}^{144}\text{Ce}$ )	143.91365
Krypton-94 ( $_{36}^{94}\text{Kr}$ )	93.93436
Neutron (n)	1.00867

Nuclide/Particle	Mass / u
Plutonium-239 ( $_{94}^{239}\text{Pu}$ )	239.05216
Xenon-134 ( $_{54}^{134}\text{Xe}$ )	133.90539
Zirconium-103 ( $_{40}^{103}\text{Zr}$ )	102.92658
Cerium-144 ( $_{58}^{144}\text{Ce}$ )	143.91365
Krypton-94 ( $_{36}^{94}\text{Kr}$ )	93.93436
Neutron (n)	1.00867
1 u is equivalent to 931.5 MeV

(a) Show that the energy released in Reaction 1 is approximately 189 MeV.

[3]

(b)

(b) Determine the energy released in Reaction 2.

[3]

(c)

[2]

(d)(i)

The reactor has a useful electrical power output of 550 MW and an overall efficiency of 32%. Assume that all fission events in the reactor follow Reaction 1.

(i) Calculate the total thermal power produced by the fission reactions.

[2]

(d)(ii)

(ii) Calculate the number of Plutonium-239 nuclei that undergo fission every second.

[3]

(d)(iii)

(iii) Calculate the mass of Plutonium-239 that undergoes fission in one week.

[3]

Question 4

EasyPaper 1A · calculator1 mark

What is the primary function of the control rods in a thermal nuclear reactor?

A. To slow down fast-moving neutrons to thermal speeds.

B. To absorb neutrons, thereby controlling the rate of fission reactions.

C. To transfer thermal energy from the reactor core to a heat exchanger.

D. To undergo fission and release energy.

Question 5

MediumPaper 2 · calculator14 marks

(a)

This question is about a nuclear reactor for a submarine.

A new design for a compact nuclear reactor for a deep-sea exploration submarine uses plutonium-239 as its fuel. The fission of a plutonium-239 nucleus is induced by a single neutron. One possible reaction is:

$^{239}_{94}\text{Pu} + ^1_0\text{n} \rightarrow ^{140}_{54}\text{Xe} + ^{97}_{40}\text{Zr} + 3(^1_0\text{n})$

(a) Explain, with reference to binding energy, why this fission reaction releases a significant amount of energy.

[3]

(b)

(b) The reaction shown in part (a) produces more neutrons than it consumes. Describe how this can lead to a self-sustaining chain reaction.

[2]

(c)(i)

(c) For the reactor to operate safely and efficiently, several key components are required. Outline the function of the following components in the submarine's reactor.

(i) The moderator.

[2]

(c)(ii)

(ii) The control rods.

[2]

(c)(iii)

(iii) The heat exchanger.

[2]

(d)

(d) The spent fuel from the submarine's reactor is highly radioactive. Discuss two problems associated with the safe disposal of this nuclear waste.

[3]

Question 6

HardPaper 2 · calculator20 marks

(a)

An exoplanet named Xylos orbits a star named Aethel. Scientists are studying its atmospheric conditions and the properties of its host star.

(a) State what is meant by the stellar constant for Xylos.

[1]

(b)(i)

(b) The following data are given for exoplanet Xylos:

Average albedo of Xylos $= 0.40$

Average orbital distance from Aethel $= 2.0 \times 10^{11} \text{ m}$

Average global surface temperature of Xylos $= 250 \text{ K}$

Luminosity of star Aethel $= 2.0 \times 10^{26} \text{ W}$

(i) Outline the physical mechanism by which some of the infrared radiation emitted by the surface of Xylos is absorbed by its atmospheric gases and re-radiated back towards the surface.

[2]

(b)(ii)

(ii) Show that the average global intensity of radiation absorbed by the surface of Xylos is about $60 \text{ W m}^{-2}$ .

[2]

(b)(iii)

(iii) Determine the average intensity re-radiated by Xylos's atmosphere towards its surface. Assume that the emissivity of the surface is $0.95$ .

[3]

(c)

[2]

(d)(i)

(d) A possible fusion reaction occurring in stars like Aethel is the deuterium-tritium (D-T) fusion reaction:

$^2_1\text{H} + ^3_1\text{H} \rightarrow ^4_2\text{He} + ^1_0\text{n}$

Relevant atomic masses are:

Mass of deuterium ( $^2_1\text{H}$ ) $= 2.013553 \text{ u}$

Mass of tritium ( $^3_1\text{H}$ ) $= 3.015501 \text{ u}$

Mass of helium-4 ( $^4_2\text{He}$ ) $= 4.001506 \text{ u}$

Mass of neutron ( $^1_0\text{n}$ ) $= 1.008665 \text{ u}$

(i) Calculate, in $\text{MeV}$ , the energy released in the reaction.

[2]

(d)(ii)

(ii) Outline the role of fusion reactions in maintaining a stable radius for a star like Aethel.

[2]

(d)(iii)

(iii) Outline how the presence of hydrogen in Aethel can be confirmed empirically.

[2]

(e)(i)

(e) Aethel has a surface temperature of $5200 \text{ K}$ and a luminosity $0.5$ times that of the Sun.

(i) State the star type of Aethel.

[1]

(e)(ii)

(ii) Discuss how nuclear fusion processes in a red dwarf star differ from those in the Sun.

[3]

Question 7

EasyPaper 1A · calculator1 mark

In a prototype fast breeder reactor, the fission of a uranium-238 nucleus by a fast neutron produces, on average, 5 neutrons.

In this reactor model:

The average number of neutrons absorbed by the moderator and control systems is $N_A$ per fission.

The average number of neutrons that escape the reactor core is $N_E$ per fission.

For the reaction to be self-sustaining and critical, one neutron from each fission must induce a subsequent fission.

What are possible average values for $N_A$ and $N_E$ for the reactor to operate at a critical state?

	$N_A$	$N_E$
A.	2	1
B.	3	1
C.	2	3
D.	4	2

Question 8

MediumPaper 1A · calculator1 mark

A proposed fusion power plant uses the reaction of one deuterium nucleus ( $^2\text{H}$ ) and one tritium nucleus ( $^3\text{H}$ ). This reaction converts a mass of $0.019\text{u}$ into energy. In a conventional fission power plant, the fission of one uranium-235 nucleus converts a mass of $0.28\text{u}$ into energy.

What is the ratio of $\frac{\text{energy released per unit mass of hydrogen fuel}}{\text{energy released per unit mass of uranium fuel}}$ ?

A. $0.068$

B. $0.31$

C. $3.2$

D. $7.9$

Question 9

EasyPaper 1A · calculator1 mark

What is the primary function of control rods in a nuclear fission reactor?

A. To slow down fast neutrons to thermal energies.

B. To absorb excess neutrons to control the reaction rate.

C. To transfer thermal energy from the reactor core.

D. To provide shielding against ionizing radiation.

Question 10

MediumPaper 1A · calculator1 mark

A nucleus of plutonium-239 ( $^{239}_{94}\text{Pu}$ ) absorbs a neutron and undergoes fission, producing two daughter nuclides, xenon-140 ( $^{140}_{54}\text{Xe}$ ) and zirconium-97 ( $^{97}_{40}\text{Zr}$ ).

How many neutrons are released in this reaction?

A. $1$

B. $2$

C. $3$

D. $4$

Question 11

EasyPaper 1A · calculator1 mark

What is the primary role of the control rods in a nuclear fission reactor?

A. To slow down the neutrons produced in fission reactions.

B. To absorb excess neutrons, thereby controlling the rate of reaction.

C. To transfer thermal energy from the reactor to a heat exchanger.

D. To prevent the escape of harmful radiation from the reactor.

Question 12

MediumPaper 1A · calculator1 mark

A reactor uses plutonium-239 ( $^{239}_{94}\text{Pu}$ ) as fuel. When a nucleus of plutonium-239 absorbs a neutron, it undergoes fission, producing barium-144 ( $^{144}_{56}\text{Ba}$ ) and strontium-94 ( $^{94}_{38}\text{Sr}$ ) as fission products.

How many neutrons are released in this reaction?

A. $1$

B. $2$

C. $3$

D. $4$

Question 13

EasyPaper 1A · calculator1 mark

What is the primary function of the control rods in a thermal nuclear reactor?

A. To slow down fast-moving neutrons to increase the probability of fission.

B. To absorb neutrons to regulate the rate of the chain reaction.

C. To transfer thermal energy from the reactor core to a secondary fluid.

D. To contain the fissile material such as Uranium-235.

Question 14

MediumPaper 1A · calculator1 mark

A graph of the variation with nucleon number $A$ of the binding energy per nucleon is shown.

Graph showing binding energy per nucleon/MeV on y-axis from 0 to 9 and nucleon number A on x-axis from 0 to 240. The graph shows a curve increasing to a peak around A=60 and then slowly decreasing.

What is the approximate total energy, in $\text{MeV}$ , needed to completely separate the nucleons of a $^{150}_{62}\text{Sm}$ nucleus?

A. $510$

B. $980$

C. $1230$

D. $1400$

Question 15

EasyPaper 1A · calculator1 mark

What is the primary role of the control rods in a thermal nuclear fission reactor?

A. To slow down neutrons produced in fission reactions.

B. To absorb some of the neutrons to control the reaction rate.

C. To act as a heat transfer medium to remove energy from the core.

D. To provide the fissile material for the chain reaction.

Question 16

MediumPaper 1A · calculator1 mark

Consider the operation of a nuclear fission power plant. Three statements are made:

I. The rate of the chain reaction is controlled by inserting or withdrawing control rods.

II. The moderator is used to absorb the fast neutrons produced in the fission reactions.

III. Uranium fuel is enriched to increase the proportion of the fissionable isotope U-235.

Which of the statements are correct?

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

Question 17

EasyPaper 1A · calculator1 mark

In a nuclear power station, the operator needs to decrease the power output from the reactor. Which action will achieve this?

A. Inserting the control rods further into the reactor core.

B. Withdrawing the control rods from the reactor core.

C. Increasing the temperature of the moderator.

D. Decreasing the pressure of the steam in the turbine circuit.

Question 18

MediumPaper 1A · calculator1 mark

A pressurized water reactor (PWR) is a type of nuclear fission reactor. Consider the following statements about its operation:

I. In the heat exchanger, thermal energy is transferred from the primary coolant loop to a secondary water loop, producing steam to drive a turbine.

II. Withdrawing the control rods from the reactor core causes a decrease in the reactor's power output.

III. The moderator slows down fast neutrons to thermal energies, which increases the probability of them inducing further fission in uranium-235 nuclei.

Which of the statements are correct?

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

Question 19

EasyPaper 1A · calculator1 mark

A nuclear fission reactor is operating at a steady power output. Which of the following adjustments would cause the power output to begin to increase?

A. Inserting the control rods further into the reactor core.

B. Removing some of the moderator material.

C. Withdrawing the control rods partially from the reactor core.

D. Increasing the pressure within the heat exchanger.

Question 20

MediumPaper 1A · calculator1 mark

A heavy nucleus P with total binding energy $B_\text{P}$ undergoes nuclear fission into two lighter nuclei, Q and R, with total binding energies $B_\text{Q}$ and $B_\text{R}$ respectively. The reaction releases energy. What is the correct relation between these binding energies?

A. $B_\text{P} = B_\text{Q} + B_\text{R}$

B. $B_\text{P} > B_\text{Q} + B_\text{R}$

C. $B_\text{P} < B_\text{Q} + B_\text{R}$

D. $B_\text{Q} < B_\text{P} < B_\text{R}$

1 more Fission question in the app

Every answer is marked mark by mark, IB-style, and the AI tutor helps when you are stuck.

Where marks are lost

Stopping one step short of the conclusion. Two numbers and no sentence is two marks out of three.
Answering a procedure question with a platitude.
Losing precision in Paper 1B. Uniquely to this paper, quoting the right number badly loses marks.

Fission: notes and practice questions

How it is examined

Guiding questions

Linking questions

Practice questions

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question 11

Question 12

Question 13

Question 14

Question 15

Question 16

Question 17

Question 18

Question 19

Question 20

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Where marks are lost

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How it is examined

Guiding questions

Linking questions

Practice questions

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Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question 11

Question 12

Question 13

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Question 15

Question 16

Question 17

Question 18

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1 more Fission question in the app

Where marks are lost

Questions,answered.

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Questions,
answered.

Start with the IB question
bank built for you.