Define mass-energy equivalence .

Mass-energy equivalence is the principle that mass can be converted into energy , and energy can be converted into mass .

Mass-energy equivalence was proposed by .......... as part of his theory of relativity.

Mass-energy equivalence was proposed by Einstein as part of his theory of relativity.

Give two examples of processes that demonstrate mass-energy equivalence.

The fusion of hydrogen into helium in the centre of the sun The fission of uranium in nuclear power plants Nuclear weapons High-energy particle collisions in particle accelerators

True or False? According to mass-energy equivalence, energy can be converted into mass, but mass cannot be converted into energy.

False. Mass-energy equivalence works both ways: mass can be converted into energy , and energy can be converted into mass .

Mass defect is the difference between an atom's mass and the sum of the masses of its protons and neutrons.

Define binding energy .

Binding energy is the amount of energy required to separate a nucleus into its constituent protons and neutrons.

Why do nuclear reactions release far more energy than chemical reactions?

Nuclear reactions involve changes in nuclear binding energy (of the order of MeV), whereas chemical reactions involve changes in electron binding energy (of the order of eV), which is much smaller.

Define the unified atomic mass unit (u) .

The unified atomic mass unit is defined as the mass of exactly one-twelfth of an atom of carbon-12 .

How many MeV is 1 u equivalent to?

1 u is equivalent to 931.5 MeV .

True or False? The binding energy of a nucleus is the energy stored inside the nucleus.

False. Binding energy is not stored energy in the nucleus — it is the energy that must be put into the nucleus to separate all of its nucleons.

Define nuclear fusion .

Nuclear fusion is the joining together of two small nuclei to produce a larger nucleus.

Define nuclear fission .

Nuclear fission is the splitting of a large atomic nucleus into smaller nuclei.

What two forces make it difficult for two nuclei to fuse together?

Electrostatic repulsion between the positively charged protons in the nuclei The strong nuclear force , which only acts at very short distances, so the nuclei must get very close together

Fission must be .......... by firing neutrons at a nucleus.

Fission must be induced by firing neutrons at a nucleus.

True or False? During nuclear fission, the extra neutrons are ejected from the fission products.

False. The extra neutrons are ejected from the original nucleus undergoing fission, not from the fission products.

Why do both fusion and fission reactions release energy?

The daughter nuclei produced have a higher binding energy per nucleon than the parent nuclei. The resulting mass difference is released as energy.

Define binding energy per nucleon .

Binding energy per nucleon is the binding energy of a nucleus divided by the number of nucleons in the nucleus.

Which nuclide has the highest binding energy per nucleon, and what does this indicate?

Iron-56 has the highest binding energy per nucleon, making it the most stable of all the elements.

Name three nuclides that do not fit the general trend of the binding energy per nucleon graph.

Helium-4 ( 4 He) Carbon-12 ( 12 C) Oxygen-16 ( 16 O)

Nuclei with low nucleon number tend to undergo .......... , while nuclei with high nucleon number tend to undergo .......... .

Nuclei with low nucleon number tend to undergo fusion , while nuclei with high nucleon number tend to undergo fission .

How does the energy released per kilogram compare between fusion and fission?

Fusion releases much more energy per kilogram than fission .

True or False? Fusion requires less initial input of energy than fission.

False. Fusion requires a greater initial input of energy than fission, in order to overcome the electrostatic repulsion between nuclei.

State one similarity between nuclear fusion and nuclear fission in terms of mass and energy.

In both fusion and fission, the total mass of the products is slightly less than the total mass of the reactants, and this mass defect is released as energy .

Define induced nuclear fission .

Induced nuclear fission occurs when a stable nucleus splits into smaller nuclei due to the absorption of a slow-moving neutron.

Define a thermal neutron .

A thermal neutron is a neutron which is in thermal equilibrium with its surroundings.

What happens when a fast-moving neutron is incident on a uranium-235 nucleus?

The fast-moving neutron rebounds from the nucleus, rather than being absorbed to induce fission.

In a nuclear reactor, thermal neutrons correspond to a core reactor temperature of about .......... K.

In a nuclear reactor, thermal neutrons correspond to a core reactor temperature of about 300 K.

Define critical mass .

Critical mass is the minimum mass of fuel required to maintain a steady chain reaction.

What is the difference between using a subcritical mass and a supercritical mass of fuel?

Subcritical mass : the chain reaction would eventually stop Supercritical mass : the reaction runs away, eventually leading to an explosion

True or False? Fast-moving neutrons are more likely than slow-moving neutrons to induce fission in a uranium-235 nucleus.

False. Only slow-moving (thermal) neutrons can be absorbed by uranium-235 nuclei to induce fission; fast-moving neutrons simply rebound.

In addition to two daughter nuclei, how many neutrons are typically produced by a fission reaction?

Two or three neutrons are typically produced.

What is the purpose of the coolant in a nuclear reactor?

To transfer thermal energy efficiently between the water systems of a nuclear power plant.

How does raising or lowering control rods affect the rate of fission?

Lowering the rods decreases the rate of fission, as more neutrons are absorbed Raising the rods increases the rate of fission, as fewer neutrons are absorbed

Neutrons released during fission slow down through repeated .......... collisions with the moderator nuclei.

Neutrons released during fission slow down through repeated elastic collisions with the moderator nuclei.

Name two materials commonly used as a moderator, and state why they are suitable.

Graphite and water are commonly used, as they are made of light nuclei that are poor absorbers of neutrons.

True or False? Water is commonly used as both the moderator and the coolant because it is inexpensive.

False. Water is used as both moderator and coolant because it has a high specific heat capacity , allowing it to transfer large amounts of thermal energy.

Which materials are used for shielding in a nuclear reactor, and why are they needed?

Lead or concrete shielding is needed because gamma radiation is highly penetrating and cannot be stopped by a few cm of material, unlike alpha and beta radiation.

Define enriched uranium .

Enriched uranium is nuclear fuel consisting of uranium-238 with an increased proportion of uranium-235, used as fuel in nuclear reactors.

State three measures used to reduce workers' exposure to radiation at a nuclear reactor.

Fuel rods are handled remotely, by machines The reactor is surrounded by thick lead or concrete shielding In an emergency, control rods are fully lowered to absorb all free neutrons (an emergency shut-down )

Low-level waste is encased in .......... and stored a few metres underground until it can be disposed of with regular waste.

Low-level waste is encased in concrete and stored a few metres underground until it can be disposed of with regular waste.

How is intermediate-level nuclear waste stored?

Intermediate-level waste is encased in cement in steel drums and stored securely underground.

Describe the steps involved in treating high-level nuclear waste before long-term storage.

Placed in cooling ponds of water close to the reactor for a number of years Useful isotopes of plutonium and uranium are harvested for reuse Mixed with molten glass and made solid Encased in containers made from steel, lead or concrete Stored very deep underground

True or False? In a nuclear reactor, uranium-238 is the isotope that undergoes fission.

False. Uranium-235 is the isotope that undergoes fission; uranium-238 absorbs fission neutrons, helping to control the rate of the fission reaction.

State three benefits of nuclear power compared to fossil fuels.

Produces very little pollution, with no carbon dioxide or sulphur dioxide released during operation Provides a continuous, highly reliable energy output Has the highest energy density of any fuel

State three risks associated with nuclear power.

Uses a non-renewable fuel Produces radioactive waste that is dangerous and expensive to manage Risk of a nuclear meltdown , which could have catastrophic environmental and human consequences

Give the year of each of the following early milestones in the history of nuclear energy: the discovery of nuclear fission, the first chain reaction, the first use of atomic bombs, and the first nuclear fission reactor to generate electricity.

1939 – nuclear fission discovered (Hahn, Meitner and Strassmann) 1942 – first chain reaction achieved (led by Enrico Fermi) 1945 – first (and last) atomic bombs dropped, at Hiroshima and Nagasaki 1951 – first nuclear fission reactor to generate electricity

A LevelPhysicsAQAFlashcardsNuclear PhysicsNuclear Fusion & Fission

Nuclear Fusion & Fission (AQA A Level Physics): Flashcards

Exam code: 7408

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FrontEnergy & Mass Equivalence
Define mass-energy equivalence.
FrontEnergy & Mass Equivalence
State the equation for mass-energy equivalence and define each term.
BackEnergy & Mass Equivalence
$E = m c^{2}$
E = energy (J)
m = mass (kg)
c = the speed of light (m s^-1)

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Cards in this collection (55)

Define mass-energy equivalence.
Mass-energy equivalence is the principle that mass can be converted into energy, and energy can be converted into mass.
State the equation for mass-energy equivalence and define each term.
$E = m c^{2}$
- E = energy (J)
- m = mass (kg)
- c = the speed of light (m s^-1)
Mass-energy equivalence was proposed by .......... as part of his theory of relativity.
Mass-energy equivalence was proposed by Einstein as part of his theory of relativity.
Give two examples of processes that demonstrate mass-energy equivalence.
- The fusion of hydrogen into helium in the centre of the sun
- The fission of uranium in nuclear power plants
- Nuclear weapons
- High-energy particle collisions in particle accelerators
True or False?
According to mass-energy equivalence, energy can be converted into mass, but mass cannot be converted into energy.
False.
Mass-energy equivalence works both ways: mass can be converted into energy, and energy can be converted into mass.
Define mass defect.
Mass defect is the difference between an atom's mass and the sum of the masses of its protons and neutrons.
Define binding energy.
Binding energy is the amount of energy required to separate a nucleus into its constituent protons and neutrons.
State the equation used to calculate the mass defect, Δm, of a nucleus.
$Δ m = Z m_{p} + (A - Z) m_{n} - m_{t o t a l}$
- Z = proton number
- A = nucleon number
- m_p = mass of a proton (kg)
- m_n = mass of a neutron (kg)
- m_total = measured mass of the nucleus (kg)
Why do nuclear reactions release far more energy than chemical reactions?
Nuclear reactions involve changes in nuclear binding energy (of the order of MeV), whereas chemical reactions involve changes in electron binding energy (of the order of eV), which is much smaller.
1 u = .......... kg.
1 u = 1.66 × 10^-27 kg.
Define the unified atomic mass unit (u).
The unified atomic mass unit is defined as the mass of exactly one-twelfth of an atom of carbon-12.
How many MeV is 1 u equivalent to?
1 u is equivalent to 931.5 MeV.
True or False?
The binding energy of a nucleus is the energy stored inside the nucleus.
False.
Binding energy is not stored energy in the nucleus — it is the energy that must be put into the nucleus to separate all of its nucleons.
Define nuclear fusion.
Nuclear fusion is the joining together of two small nuclei to produce a larger nucleus.
Define nuclear fission.
Nuclear fission is the splitting of a large atomic nucleus into smaller nuclei.
What two forces make it difficult for two nuclei to fuse together?
- Electrostatic repulsion between the positively charged protons in the nuclei
- The strong nuclear force, which only acts at very short distances, so the nuclei must get very close together
State the equation for the deuterium–tritium (D–T) fusion reaction.
$_1^{2} H +_1^{3} H \to_2^{4} H e +_0^{1} n$
Fission must be .......... by firing neutrons at a nucleus.
Fission must be induced by firing neutrons at a nucleus.
State the equation used to calculate the binding energy released in a nuclear reaction.
$E = Δ m c^{2}$
- E = binding energy released (J)
- Δm = mass defect (kg)
- c = speed of light (m s^-1)
True or False?
During nuclear fission, the extra neutrons are ejected from the fission products.
False.
The extra neutrons are ejected from the original nucleus undergoing fission, not from the fission products.
Why do both fusion and fission reactions release energy?
The daughter nuclei produced have a higher binding energy per nucleon than the parent nuclei. The resulting mass difference is released as energy.
Define binding energy per nucleon.
Binding energy per nucleon is the binding energy of a nucleus divided by the number of nucleons in the nucleus.
Which nuclide has the highest binding energy per nucleon, and what does this indicate?
Iron-56 has the highest binding energy per nucleon, making it the most stable of all the elements.
Name three nuclides that do not fit the general trend of the binding energy per nucleon graph.
- Helium-4 (⁴He)
- Carbon-12 (¹²C)
- Oxygen-16 (¹⁶O)
Nuclei with low nucleon number tend to undergo .........., while nuclei with high nucleon number tend to undergo ...........
Nuclei with low nucleon number tend to undergo fusion, while nuclei with high nucleon number tend to undergo fission.
How does the energy released per kilogram compare between fusion and fission?
Fusion releases much more energy per kilogram than fission.
True or False?
Fusion requires less initial input of energy than fission.
False.
Fusion requires a greater initial input of energy than fission, in order to overcome the electrostatic repulsion between nuclei.
State one similarity between nuclear fusion and nuclear fission in terms of mass and energy.
In both fusion and fission, the total mass of the products is slightly less than the total mass of the reactants, and this mass defect is released as energy.
Define induced nuclear fission.
Induced nuclear fission occurs when a stable nucleus splits into smaller nuclei due to the absorption of a slow-moving neutron.
Define a thermal neutron.
A thermal neutron is a neutron which is in thermal equilibrium with its surroundings.
What happens when a fast-moving neutron is incident on a uranium-235 nucleus?
The fast-moving neutron rebounds from the nucleus, rather than being absorbed to induce fission.
In a nuclear reactor, thermal neutrons correspond to a core reactor temperature of about .......... K.
In a nuclear reactor, thermal neutrons correspond to a core reactor temperature of about 300 K.
Define critical mass.
Critical mass is the minimum mass of fuel required to maintain a steady chain reaction.
What is the difference between using a subcritical mass and a supercritical mass of fuel?
- Subcritical mass: the chain reaction would eventually stop
- Supercritical mass: the reaction runs away, eventually leading to an explosion
True or False?
Fast-moving neutrons are more likely than slow-moving neutrons to induce fission in a uranium-235 nucleus.
False.
Only slow-moving (thermal) neutrons can be absorbed by uranium-235 nuclei to induce fission; fast-moving neutrons simply rebound.
In addition to two daughter nuclei, how many neutrons are typically produced by a fission reaction?
Two or three neutrons are typically produced.
What is the purpose of a moderator in a nuclear reactor?
To slow down neutrons.
What is the purpose of control rods in a nuclear reactor?
To absorb neutrons.
What is the purpose of the coolant in a nuclear reactor?
To transfer thermal energy efficiently between the water systems of a nuclear power plant.
How does raising or lowering control rods affect the rate of fission?
- Lowering the rods decreases the rate of fission, as more neutrons are absorbed
- Raising the rods increases the rate of fission, as fewer neutrons are absorbed
Neutrons released during fission slow down through repeated .......... collisions with the moderator nuclei.
Neutrons released during fission slow down through repeated elastic collisions with the moderator nuclei.
Approximately how many collisions does it take for a fast neutron to slow down to become a thermal neutron in the moderator?
About fifty collisions.
Name two materials commonly used as a moderator, and state why they are suitable.
Graphite and water are commonly used, as they are made of light nuclei that are poor absorbers of neutrons.
Name two materials commonly used for control rods.
- Boron
- Cadmium
True or False?
Water is commonly used as both the moderator and the coolant because it is inexpensive.
False.
Water is used as both moderator and coolant because it has a high specific heat capacity, allowing it to transfer large amounts of thermal energy.
Which materials are used for shielding in a nuclear reactor, and why are they needed?
Lead or concrete shielding is needed because gamma radiation is highly penetrating and cannot be stopped by a few cm of material, unlike alpha and beta radiation.
Define enriched uranium.
Enriched uranium is nuclear fuel consisting of uranium-238 with an increased proportion of uranium-235, used as fuel in nuclear reactors.
State three measures used to reduce workers' exposure to radiation at a nuclear reactor.
- Fuel rods are handled remotely, by machines
- The reactor is surrounded by thick lead or concrete shielding
- In an emergency, control rods are fully lowered to absorb all free neutrons (an emergency shut-down)
Low-level waste is encased in .......... and stored a few metres underground until it can be disposed of with regular waste.
Low-level waste is encased in concrete and stored a few metres underground until it can be disposed of with regular waste.
How is intermediate-level nuclear waste stored?
Intermediate-level waste is encased in cement in steel drums and stored securely underground.
Describe the steps involved in treating high-level nuclear waste before long-term storage.
- Placed in cooling ponds of water close to the reactor for a number of years
- Useful isotopes of plutonium and uranium are harvested for reuse
- Mixed with molten glass and made solid
- Encased in containers made from steel, lead or concrete
- Stored very deep underground
True or False?
In a nuclear reactor, uranium-238 is the isotope that undergoes fission.
False.
Uranium-235 is the isotope that undergoes fission; uranium-238 absorbs fission neutrons, helping to control the rate of the fission reaction.
State three benefits of nuclear power compared to fossil fuels.
- Produces very little pollution, with no carbon dioxide or sulphur dioxide released during operation
- Provides a continuous, highly reliable energy output
- Has the highest energy density of any fuel
State three risks associated with nuclear power.
- Uses a non-renewable fuel
- Produces radioactive waste that is dangerous and expensive to manage
- Risk of a nuclear meltdown, which could have catastrophic environmental and human consequences
Give the year of each of the following early milestones in the history of nuclear energy: the discovery of nuclear fission, the first chain reaction, the first use of atomic bombs, and the first nuclear fission reactor to generate electricity.
- 1939 – nuclear fission discovered (Hahn, Meitner and Strassmann)
- 1942 – first chain reaction achieved (led by Enrico Fermi)
- 1945 – first (and last) atomic bombs dropped, at Hiroshima and Nagasaki
- 1951 – first nuclear fission reactor to generate electricity

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