Nuclear fission

This question is about using radioactivity and nuclear energy.

Gamma ray irradiation of food kills harmful bacteria by using

Which part of a nuclear reactor is used to absorb neutrons?

The isotope fluorine-18 is used in PET scans, which help to detect cancers.

Figure 20 shows a radioactive decay curve for a sample of fluorine-18.

Use the graph to calculate the percentage of fluorine-18 remaining after 150 minutes.

percentage of fluorine-18 remaining after 150 minutes =_........

Fluorine-18 releases positrons.

Describe what happens when positrons meet electrons.

Figure 21 shows what happens during a fission chain reaction.

Explain what happens when one neutron interacts with one uranium nucleus.

In 2023, Finland produced 4.4 GW of power from nuclear power plants.

The UK produced 8.9 GW of power from nuclear power plants.

Calculate the ratio of nuclear power produced in Finland compared with the UK as

power production in Finland

Give your answer to 2 significant figures (2 s.f.).

This question is about using radioactivity and nuclear energy.

Gamma ray irradiation of food kills harmful bacteria by using

Which part of a nuclear reactor is used to absorb neutrons?

The isotope fluorine-18 is used in PET scans, which help to detect cancers.

Figure 7 shows a radioactive decay curve for a sample of fluorine-18.

Use the graph to calculate the percentage of fluorine-18 remaining after 150 minutes.

percentage of fluorine-18 remaining after 150 minutes =_........

Fluorine-18 releases positrons.

Describe what happens when positrons meet electrons.

Figure 8 shows what happens during a fission chain reaction.

Explain what happens when one neutron interacts with one uranium nucleus.

In 2023, Finland produced 4.4 GW of power from nuclear power plants.

The UK produced 8.9 GW of power from nuclear power plants.

Calculate the ratio of nuclear power produced in Finland compared with the UK as

power production in Finland

Give your answer to 2 significant figures (2 s.f.).

Figure 20 shows a Mars rover, a vehicle used for exploring the surface of the planet Mars.

(Source: © BEST-BACKGROUNDS/Shutterstock)

Figure 20

The power supply in a Mars rover is called an RTG.

The RTG contains a radioactive isotope that releases thermal energy as it decays.

The RTG uses the thermal energy released in the decay to provide electrical power for the rover.

An RTG has an efficiency rating of only 7%.

Calculate the useful energy transferred by the RTG when 1300 J of thermal energy is released in the decay.

Use the equation useful energy transferred by the device efficiency = × 100% total energy supplied to the device

Suggest, with a reason, one property the isotope must have to be suitable for use in the RTG.

Figure 21 shows the fission of a uranium nucleus.

Nuclear fission
free neutron

(Source: adapted from © 1501926062/Shutterstock)

Figure 21

The total mass of all the particles after the reaction is less than the total mass of the particles before the reaction.

The energy released in the reaction comes from the change in mass.

This is shown in the equation

energy released = (change in mass) × (speed of light)²

The energy released in one fission reaction = 1.49 × 10^–10J.

The speed of light = 3.00 × 10⁸m / s.

Calculate the change in mass.

*(c) The energy released in a single uranium fission is very small.

In a nuclear power station, the fission of uranium in the reactor releases large amounts of energy.

The energy released is enough to generate electricity for thousands of homes.

The demand for electricity varies.

Explain

• how large amounts of energy can be released in the reactor

• how the rate of energy release is controlled as the demand for electricity varies.

Equations

Radioactive tracers can be used when scanning a person’s kidneys.

A radioactive isotope is injected into a person’s blood stream.

The isotope emits radiation.

As the blood flows through the kidneys, this radiation is detected outside the body by a scanner.

What type of radiation travels from the kidney to the scanner?

During the scan, a technician needs to take readings for about 30 minutes.

The half‑life of the isotope used is about 6 hours.

1. State why an isotope with a half‑life of about 6 minutes is not suitable.

2. State why an isotope with a half‑life of about 6 days is not suitable.

State two ways of reducing the radiation risks to the technician.

Figure 17 is a diagram of a nuclear reactor.

Explain how pushing the control rods further into the reactor slows down the nuclear chain reaction.

The moderator in a nuclear reactor slows down the neutrons so that the neutrons are more likely to start other fission reactions.

In a nuclear reactor,

• the average speed of the fast neutrons is 3.010⁷m/s

• the average speed of the slow neutrons is 4.010³m/s

Calculate the average speed of the slow neutrons as a percentage of the average speed of the fast neutrons.

The nuclear reaction is the first stage in the process of generating electricity.

Describe how energy is transferred from the nuclear reaction to the next stage in the process.

Equations

Radioactive tracers can be used when scanning a person’s kidneys.

A radioactive isotope is injected into a person’s blood stream.

The isotope emits radiation.

As the blood flows through the kidneys, this radiation is detected outside the body by a scanner.

What type of radiation travels from the kidney to the scanner?

During the scan, a technician needs to take readings for about 30 minutes.

The half‑life of the isotope used is about 6 hours.

1. State why an isotope with a half‑life of about 6 minutes is not suitable.

2. State why an isotope with a half‑life of about 6 days is not suitable.

State two ways of reducing the radiation risks to the technician.

Figure 6 is a diagram of a nuclear reactor.

Explain how pushing the control rods further into the reactor slows down the nuclear chain reaction.

The moderator in a nuclear reactor slows down the neutrons so that the neutrons are more likely to start other fission reactions.

In a nuclear reactor,

• the average speed of the fast neutrons is 3.010⁷m/s

• the average speed of the slow neutrons is 4.010³m/s

Calculate the average speed of the slow neutrons as a percentage of the average speed of the fast neutrons.

The nuclear reaction is the first stage in the process of generating electricity.

Describe how energy is transferred from the nuclear reaction to the next stage in the process.

This question is about nuclear reactions.

When a uranium-235 (U-235) nucleus absorbs a neutron, the nucleus splits into smaller parts.

This reaction is called nuclear fission.

How many daughter nuclei are produced from the fission of one nucleus of uranium-235 (U-235)?

When a uranium-235 (U-235) nucleus splits, neutrons are also emitted.

The neutrons may start a chain reaction.

Describe what is meant by a chain reaction.

You may draw a diagram to help with your answer.

In the nuclear reactor of a power station, the chain reaction has to be controlled.

Explain the action of a moderator in a nuclear reactor.

In a nuclear reactor there are 2.010¹⁷ fission reactions each second.

Each fission reaction releases 4.010^–11J of energy.

Calculate the energy released in 1 second.

Nuclear fusion is a nuclear reaction that takes place in the Sun.

Describe what happens during a nuclear fusion reaction.

Figure 13 shows wind turbines, used to generate electricity for the National Grid.

The wind turns the turbine blades.

The wind is a renewable source of energy.

State two other renewable sources of energy.

For one turbine

• the energy input per second from the wind is 6.2 kJ

• the energy output per second to the National Grid is 2.2 kJ.

Calculate the efficiency of this turbine.

Suggest a reason why it is impossible for the turbine to use all the kinetic energy of the wind.

*(b) Nuclear fission and nuclear fusion are two non-renewable sources of energy.

Compare nuclear fission and nuclear fusion as possible sources of energy for generating electricity using a nuclear reactor.

Your comparison should refer to

• the differences between nuclear fission and nuclear fusion

• the relative advantages and difficulties involved in using these sources.

Use words from the box to complete the sentences about nuclear fission of uranium‑235 (U‑235).

A neutron hits a nucleus of U‑235 and causes the nucleus to_........ .

Each fission releases energy, two daughter nuclei and some_........ .

In a nuclear reactor, one fission can set off a controlled_........ reaction.

Both U‑235 and oil can be used as energy sources for generating electricity.

1 kg of natural uranium can result in the generation of 45 000 units of electricity.

1 kg of oil can result in the generation of 5.0 units of electricity.

Calculate the mass of oil needed to generate the same amount of electricity as 1 kg of natural uranium.

mass of oil =_........

Both using nuclear fuel and burning oil produce harmful waste products.

State one harmful waste product from each process.

using nuclear fuel_........

*(d) Figure 14 shows a household smoke alarm that uses radioactivity to detect smoke.

The radioactive source in the smoke detector is americium–241.

The table in Figure 15 shows some information about americium–241 and two other radioactive sources.

Explain why americium‑241 is the best of these three sources to use in this smoke detector.

Use information from Figure 15 and your own knowledge about radiation.

Your answer should refer to

• properties of alpha and gamma radiation

• half‑life.

Radioactive substances are used in the generation of electricity.

State two other uses of radioactive substances.

Figure 1 is a diagram of a nuclear reactor, used in the generation of electricity.

P may be used to shut down the reactor when necessary. Q slows down neutrons to enable a chain reaction to take place.

State the name of the two parts labelled P and Q.

Explain how neutrons enable a nuclear chain reaction to take place.

Energy from the nuclei of atoms can be used in medical diagnosis and treatment.

Fluorine‑18 is a radioactive isotope used in PET scanners for medical diagnosis.

Explain why fluorine‑18 must be produced close to the hospital where it is used.

Some tumours inside the body can be treated by using either alpha radiation or gamma radiation.

Explain why the source of alpha radiation is usually inside the body but the source of gamma radiation can be outside the body.

In a controlled chain reaction of uranium-235, which of these could cause a uranium-235 nucleus to undergo fission?

The kinetic energy of one of the particles released in a fission reaction is 1.210^–11J.

The mass of the particle is 1.410^–25kg.

Calculate the velocity of the particle.

Figure 8 shows a helium nucleus.

Two of the particles in the helium nucleus are neutrons.

State the name of the other two particles in the helium nucleus.

Describe the difference between a fusion reaction and a fission reaction.

Nuclear fusion does not happen at low temperatures because of electrostatic repulsion between

The energy released per kilogram of fuel in a fusion reaction is 845 000 GJ.

The energy released per kilogram of fuel in burning oil is 0.0394 GJ.

Calculate the ratio of the energy released in fusion compared with the energy released in burning oil.

Use the equation

State two advantages of using a fusion reactor rather than burning oil in a power station.

State two of the difficulties that need to be overcome to produce a fusion reactor.

Fusion and fission are nuclear reactions in which large amounts of energy are released.

In a fusion reaction, two hydrogen nuclei are forced together to form a helium nucleus.

Explain why a very high temperature is needed for this reaction to happen.

In a fusion reaction, the combined mass of the two small nuclei is greater than the mass of the resulting nucleus.

This decrease in mass, m, appears as energy, E, according to the equation.

c is the speed of light = 3.0 × 10⁸ m/s.

The energy released in one fusion reaction is 4.5 × 10⁻¹² J.

Calculate the decrease in mass.

*(b) Nuclear fission is used in nuclear reactors in some power stations.

In the reactor, a fission chain reaction is maintained and controlled to produce a supply of energy to generate electricity.

Figure 14 is a diagram of a nuclear reactor.

Explain how the graphite core and the movable rods are used to maintain and control the chain reaction.