Half-life

Unstable isotopes of elements decay by emitting nuclear radiation.

What is the difference between the atoms of isotopes of the same element?

Tick (✓) one box.

The number of electrons in an atom

The number of neutrons in an atom

The number of protons in an atom

Draw one line from each type of radiation to the description of the radiation.

A radioactive source emits alpha, beta and gamma radiation.

Which type of radiation from the source can pass through 5 mm of aluminium?

Which type of radiation from the source is stopped by a sheet of paper?

Caesium-137 (Cs) decays into barium-137 (Ba) by emitting beta radiation (β).

Which of the following is the decay equation for caesium-137?

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In 2011, an accident at a nuclear power station caused the release of radioactive elements into the environment.

Two of the radioactive elements released were iodine-131 and xenon-133

Figure 4 shows how the radiation emitted each second changes with time.

How does the half-life of xenon-133 compare with the half-life of iodine-131?

Give a reason for your answer.

Use Figure 4.

Tick (✓) one box.

The half-life of xenon-133 is less than the half-life of iodine-131

The half-life of xenon-133 is the same as the half-life of iodine-131

The half-life of xenon-133 is greater than the half-life of iodine-131

In the 2011 accident, the radioactive element caesium-137 was also released into the environment.

The half-life of caesium-137 is 30 years.

Why does the caesium-137 that was released still emit large amounts of radiation in 2025?

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Less than one half-life has occurred since the accident.

Exactly one half-life has occurred since the accident.

More than one half-life has occurred since the accident.

Unstable isotopes of elements decay by emitting alpha, beta or gamma radiation.

Give one similarity and one difference in the nuclei of two isotopes of the same element.

Describe the penetration properties of alpha, beta and gamma radiation.

Caesium-137 decays to barium by emitting beta radiation.

137 Complete the nuclear equation for the decay of caesium-137 (₅₅ Cs) to barium (Ba).

In 2011, an accident at a nuclear power station caused the release of radioactive isotopes into the environment.

Table 3 gives information about the radioactive isotopes released.

What is meant by ‘half-life’?

A soil sample was taken from the area around the nuclear power station just after the accident in 2011.

The soil sample was contaminated with equal numbers of atoms of caesium-137 and iodine-131

Explain how the risk linked to each isotope has changed between 2011 and 2024.

Use information from Table 3.

Ionising radiation is dangerous to humans because it causes mutations which can cause cancer.

Which of the following can be mutated by ionising radiation?

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Atoms

Genes

Red blood cells

A nucleus of uranium-238 (U) emits an alpha particle (He) and decays into thorium-234 (Th).

Complete the nuclear equation to show the decay of a uranium-238 nucleus by emitting an alpha particle.

Rocks from a uranium mine contain uranium and several other radioactive isotopes.

Table 4 shows information about two isotopes in a sample of rock from a uranium mine.

The initial number of nuclei of each isotope in the sample was the same.

Explain the difference in the number of nuclei of each isotope in the sample after 5.0 days.

Your answer should include calculations.

Scientists collected data about lung cancer in the population of one country.

They used the data to predict the number of cases of lung cancer in people who work in uranium mines.

Table 5 shows the predicted number and the actual number of cases.

What was the percentage increase in the actual number of cases compared with the predicted number of cases?

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185%

440%

540%

Radon is an odourless, colourless gas that builds up in uranium mines.

Radon nuclei emit alpha radiation.

Explain why the actual number of cases of lung cancer in Table 5 is greater than the predicted number.

Carbon is an element with several isotopes.

An isotope of carbon is carbon-14

Plants contain carbon-14

How does carbon-14 pass from plants to animals?

Carbon-14 is radioactive.

Carbon-14 nuclei emit beta particles.

A beta particle is an electron.

Which symbol represents a beta particle?

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When a carbon-14 nucleus emits a beta particle, the atomic number changes from 6 to 7

Which element has the atomic number of 7?

Use the periodic table.

Tick (✓) one box.

Helium

Lithium

Nitrogen

Which two of the following substances would beta particles not be able to penetrate?

Tick (✓) two boxes.

1 metre of concrete

10 centimetres of lead

1 centimetre of air

1 millimetre of aluminium

0.1 millimetre sheet of paper

In 1991, the frozen remains of a human body were found in a glacier.

The body was 5400 years old.

The body tissues had not decayed completely.

What causes the decay of body tissues?

Tick (✓) one box.

Carbon dioxide

Microorganisms

Mineral ions

The percentage of carbon-14 in an organism decreases after death.

Figure 3 shows how the percentage of carbon-14 nuclei remaining varies with time.

Determine the percentage of carbon-14 nuclei remaining in an organism after 3000 years.

Use Figure 3.

The half-life of carbon-14 is the average time taken for the number of carbon-14 nuclei in a sample to halve.

Determine the half-life of carbon-14

Use Figure 3.

Only a very small proportion of the carbon in an organism is carbon-14.

Scientists studying the body from the glacier were not concerned about the risk from beta radiation emitted by the body.

Why was the risk to the scientists low?

Tick (✓) one box.

The beta radiation emitted by the body was a type of ionising radiation.

The carbon-14 nuclei in the body had all decayed.

The radiation dose absorbed by the scientists was low.

Carbon-12 (¹²C) and carbon-14 (¹⁴C) are isotopes of carbon.

Carbon-14 is radioactive.

How are the numbers and type of sub-atomic particles in carbon-14 different from the sub-atomic particles in carbon-12?

Carbon-14 is formed in the atmosphere.

Carbon-14 reacts with oxygen to produce carbon dioxide.

Explain why animal tissues contain carbon-14

Carbon-14 emits beta radiation.

Complete the nuclear equation to show the radioactive decay of carbon-14

Use the periodic table.

In 1991 the frozen remains of a human body were found in a glacier.

The carbon-14 in the body was used to determine the age of the body.

The body was 5400 years old.

Explain why the body tissues had not decayed completely.

The amount of carbon-14 in the body had decreased by 47%.

What is the half-life of carbon-14?

Tick (✓) one box.

< 5400 years = 5400 years > 5400 years

A student made a statement about a sample of a different radioactive substance.

The student stated:

‘If the half-life of the radioactive substance is 30 years, a sample of the substance will not be radioactive after 60 years.’

Explain why the student’s statement is not correct.

In 1986 an accident destroyed a nuclear power station.

Radioactive caesium-137 was released into the environment.

A nucleus of caesium-137 emits a high-speed electron when it decays.

What type of radiation does a nucleus of caesium-137 emit when it decays?

Tick (✓) one box.

Alpha

Beta

Gamma

Figure 2 shows how the percentage of caesium-137 nuclei remaining in a sample changes with time.

After one half-life, 50% of the caesium-137 nuclei remain in the sample.

What is the half-life of caesium-137?

Use Figure 2.

A sample of caesium-137 has a mass of 32 kg.

What mass of caesium-137 remains after two half-lives?

Tick (✓) one box.

4 kg 8 kg 16 kg 64 kg

Scientists investigated the effect of radiation on the dragonfly population near the nuclear power station site.

Dragonflies are insects.

The scientists recorded the number of dragonflies and level of radiation at different distances from the nuclear power station.

The scientists used a transect.

What is a transect?

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A line that is sampled along

A quadrat placed randomly

A sample at one location

Radiation from the nuclear power station caused the dragonfly population to decrease.

Nuclear radiation is an abiotic factor affecting the dragonfly population.

Which are two other abiotic factors that could affect the dragonfly population?

Tick (✓) two boxes.

Air temperature

Other insects

Predators

Prey

Water

In 1986 an accident at a nuclear power station released radioactive isotopes into the environment.

Radioactive isotopes have a half-life.

What is meant by ‘half-life’?

During the accident, 28 kg of caesium-137 was released into the environment.

Caesium-137 has a half-life of 30 years.

Calculate the mass of the caesium-137 released in 1986 that will still be present in the environment in 2136.

Give your answer in grams.

After the accident scientists investigated the effect of ionising radiation on the population of dragonflies.

Dragonflies are insects.

The scientists placed transects in different directions from the site of the nuclear power station.

The scientists recorded the number of dragonflies and the ionising radiation dose along the transects.

Figure 7 shows the results.

Describe the relationship between the ionising radiation dose and the number of dragonflies.

Suggest one abiotic factor that could affect this investigation.

Do not refer to ionising radiation dose in your answer.

Explain how the ionising radiation dose can affect the dragonfly population.