Half-life

Different radioactive isotopes emit different types of radiation.

One isotope of uranium (U) decays into thorium (Th) by emitting an alpha particle (He).

Which nuclear equation shows the decay of this isotope of uranium?

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Figure 4 shows how the percentage of uranium atoms in a sample of one uranium isotope varies with time.

What is the time taken for 50% of the atoms of this uranium isotope to decay?

Use Figure 4.

What is the half-life of this uranium isotope?

Figure 5 shows how the percentage of uranium atoms varies with time for three different isotopes of uranium, A, B and C.

Figure 5

Which isotope is the most unstable?

Give a reason for your answer.

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Figure 6 shows the nuclei of four different atoms.

Which nucleus in Figure 6 has the smallest mass number?

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Which nucleus in Figure 6 has an atomic number of 4?

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Which two nuclei in Figure 6 are isotopes of the same element?

Give a reason for your answer.

Scientists have replaced old models of the atom with newer models.

The nuclear model of the atom has a nucleus at the centre.

Which model of the atom was replaced by the nuclear model?

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What does the nuclear model state about the mass of an atom?

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Some atoms emit radiation.

Why do scientists sometimes change the model used to describe the structure of the atom?

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When radioactivity was discovered, the dangers of radiation were not known.

Some scientists were irradiated and contaminated while working with the radioactive materials.

Describe the difference between irradiation and radioactive contamination.

Polonium-210 was one of the first radioactive elements to be discovered.

Polonium-210 (Po) decays into lead (Pb).

Complete the nuclear equation for polonium-210.

Polonium-210 has a half-life of 138 days.

A sample of polonium contains 256 000 atoms.

Calculate the time taken for the number of polonium-210 atoms to reach 16 000.

A sample of polonium contains equal numbers of polonium-209 atoms and polonium-210 atoms.

Polonium-209 has a half-life of 125 years.

Polonium-210 has a half-life of 138 days.

Explain how the activity of polonium-209 compares with the activity of polonium-210 in this sample.

The process of nuclear fission is used in nuclear power stations.

Figure 17 shows the process of nuclear fission.

Complete the sentences.

Choose answers from the box.

In nuclear power stations, energy is released from

The uranium in Figure 17 splits into two parts and

The process of nuclear fission releases electromagnetic radiation in the

Use the Physics Equations Sheet to answer questions 10.2 and 10.3.

Write down the equation which links energy (E), power (P) and time (t).

A nuclear power station has a power output of 500 MW.

Calculate the energy output in 3600 s.

Give your answer in J.

Radioactive waste produced by nuclear power stations has a long half-life.

Suggest one precaution taken to reduce the hazard caused by radioactive waste from power stations.

Nuclear power stations do not generate electricity every day of the year.

One nuclear power station generated electricity for 92% of a year.

one year = 365 days

Calculate the number of days during the year that the nuclear power station generated electricity.

The process of nuclear fission is used in nuclear power stations.

Figure 2 shows the process of nuclear fission.

Complete the sentences.

Choose answers from the box.

In nuclear power stations, energy is released from

uranium.

The uranium in Figure 2 splits into two parts and

releases three.

The process of nuclear fission releases electromagnetic radiation in the

form of.

Use the Physics Equations Sheet to answer questions 02.2 and 02.3.

Write down the equation which links energy (E), power (P) and time (t).

A nuclear power station has a power output of 500 MW.

Calculate the energy output in 3600 s.

Give your answer in J.

Radioactive waste produced by nuclear power stations has a long half-life.

Suggest one precaution taken to reduce the hazard caused by radioactive waste from power stations.

Nuclear power stations do not generate electricity every day of the year.

One nuclear power station generated electricity for 92% of a year.

one year = 365 days

Calculate the number of days during the year that the nuclear power station generated electricity.

Some isotopes emit nuclear radiation.

Carbon-12 and carbon-14 are both isotopes of carbon.

Complete the sentences.

Choose answers from the box.

The nucleus of a carbon-12 atom and the nucleus of a carbon-14 atom have the

same number of.

The nucleus of a carbon-12 atom and the nucleus of a carbon-14 atom have a

different number of.

Different radioactive isotopes have different half-lives.

What does ‘half-life’ mean?

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Table 2 shows the half-life of some different isotopes of carbon.

Which isotope is the least stable?

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Workers in nuclear power stations must be aware of nuclear irradiation and radioactive contamination.

Draw one line from each term to an example of the term.

Why are workers required to walk across a sticky floor before leaving the nuclear power station?

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The places where people work and live contribute to the nuclear radiation they are exposed to.

Table 3 shows the mean daily dose of radiation caused by two different jobs.

Calculate the number of days a nuclear power station worker must work before receiving the same dose that an aeroplane pilot receives in one day.

The process of nuclear fission takes place in nuclear power stations.

The process of nuclear fusion takes place in the Sun.

Draw one line from each process to its fuel.

Some isotopes emit nuclear radiation.

Carbon-14 and carbon-12 are isotopes of carbon. Compare the structure of an atom of carbon-14 with the structure of an atom of carbon-12.

Carbon-14 is a radioactive isotope. Carbon-14 has a half-life of 5700 years. What does ‘a half-life of 5700 years’ mean?

Table 1 gives the half-life of some other radioactive isotopes.

A sample of fluorine-17 has an activity that is one quarter of its original activity. Calculate the age of the sample of fluorine-17.

All of the isotopes in Table 1 emit beta radiation. Explain which isotope would cause the biggest risk to a person’s health based only on the half-life of each isotope.

People who work in the nuclear power industry need to be aware of irradiation and contamination. Describe the difference between irradiation and contamination.

Give one health risk to a person working close to a source of nuclear radiation.

Workers in nuclear power stations are monitored to check the radiation they emit. A worker stands 1 cm away from a radiation detector. The amount of radiation the worker emits is recorded. Explain why the worker needs to stand close to the radiation detector.

Workers in the nuclear power industry are exposed to nuclear radiation. Pilots on aircraft are exposed to cosmic radiation from space. daily dose caused by working in a nuclear power station = 0.00050 mSv hourly dose from cosmic rays to a pilot while flying = 0.0030 mSv Calculate the number of days it takes for a nuclear power station worker to receive the same dose as a pilot flying for 24 hours.

Atoms of different elements have different properties.

Which of the following is the same for all atoms of the same element?

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Which of the following is different for isotopes of the same element?

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A nucleus emits radiation.

Figure 7 shows how the mass number and the atomic number change.

The nucleus is labelled D.

Which type of radiation is emitted when nucleus D decays?

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Nucleus E also emits radiation.

Figure 8 shows how the mass number and the atomic number change for nucleus E.

Which type of radiation is emitted when nucleus E decays?

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Beta radiation can be used to monitor the thickness of paper during production.

Figure 9 shows how the radiation is used.

The computer uses information from the radiation detector to change the size of the gap between the rollers.

Complete the sentences.

Choose answers from the box.

Each answer can be used once, more than once or not at all.

The thickness of the paper between the beta source and the detector increases.

This is because the amount of radiation absorbed by the paper

All radioactive elements have a half-life.

What is meant by ‘half-life’?

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Why should the radiation source used in Figure 9 have a long half-life?

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Figure 6 shows the mass number and the atomic number for the nuclei of five different atoms.

How many neutrons are there in a nucleus of atom A ?

Which two atoms in Figure 6 are the same element? Tick (✓) one box.

Nucleus B decays by emitting an alpha particle. Draw an arrow on Figure 7 to represent the alpha decay.

What is meant by the ‘random nature of radioactive decay’?

A polonium (Po) nucleus decays by emitting an alpha particle and forming a lead (Pb) nucleus. Po → Pb + α The lead (Pb) nucleus then decays by emitting a beta particle and forms a bismuth (Bi) nucleus. Pb → Bi + β The bismuth (Bi) nucleus then decays by emitting a beta particle and forms a polonium (Po) nucleus. Bi → Po + β

Explain how these three decays result in a nucleus of the original element, polonium.

Radioactive waste from nuclear power stations is a man-made source of background radiation.

Which of the following is also a man-made source of background radiation? Tick (✓) one box.

Nuclear power stations use the process of nuclear fission. Complete the sentences to describe the process of nuclear fission. Choose answers from the box.

Plutonium-239 is one type of radioactive waste from nuclear power stations. The following nuclear equation represents the decay of plutonium-239 (Pu-239). 239 235 4

How does the nuclear equation show that alpha radiation is emitted when plutonium-239 decays?

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Figure 8 shows how the activity of a sample of plutonium-239 varies with time.

How much time will it take for the activity of the sample of plutonium-239 to fall to half of its initial activity?

What is the half-life of plutonium-239?

The radioactive waste from a nuclear power station is buried underground. People are warned to stay away from places where radioactive waste is buried. Suggest one risk of going near the place where radioactive waste is buried.

Radioactive waste from nuclear power stations is a man-made source of background radiation.

Give one other man-made source of background radiation.

Nuclear power stations use the energy released by nuclear fission to generate electricity.

Give the name of one nuclear fuel.

Nuclear fission releases energy. Describe the process of nuclear fission inside a nuclear reactor.

A new type of power station is being developed that will generate electricity using nuclear fusion. Explain how the process of nuclear fusion leads to the release of energy.

Nuclear fusion power stations will produce radioactive waste. This waste will have a much shorter half-life than the radioactive waste from a nuclear fission power station. Explain the advantage of the radioactive waste having a shorter half-life.

Polonium-210 is a radioactive isotope that decays by emitting alpha radiation.

Which is the correct decay equation for polonium-210?

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Why is alpha radiation dangerous inside the human body?

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Figure 3 shows how the mass of a sample of polonium-210 changes with time.

Determine the change in mass of the sample of polonium-210 between 50 and 150 days.

Estimate the mass of polonium-210 remaining after 300 days.

Nuclear radiation can cause ionisation. Complete the sentences. Choose answers from the box.

The resulting ion has charge.

Polonium-210 is a radioactive isotope that decays by emitting alpha radiation.

Complete the decay equation for polonium-210

Explain why contamination of the inside of the human body by a radioactive material that emits alpha radiation is highly dangerous.

A sample of polonium-210 was left for 414 days.

After this time it had a mass of 1.45 × 10^-4 g

The half-life of polonium-210 is 138 days.

Calculate the initial mass of the sample.

Americium-241 ²⁴¹₉₅Am is an isotope of americium.

Which of the isotopes given in Table 1 is not an isotope of americium?

Give a reason for your answer.

Figure 5 shows how the number of americium-241 nuclei in a sample changes with time.

How many years does it take for the number of americium-241 nuclei to decrease from 10 000 to 5000?

What is the half-life of americium-241?

Smoke alarms contain an alpha radiation source and a radiation detector.

Figure 9 shows part of the inside of a smoke alarm.

The smoke alarm stays off while alpha radiation reaches the detector.

Why does the alarm switch on when smoke particles enter the plastic casing?

Why is it safe to use a source of alpha radiation in a house?

The smoke alarm would not work with a radiation source that emits beta or gamma radiation.

Explain why.

Figure 10 shows how the count rate detected from the radiation source in the smoke alarm changes with time.

Figure 10

The smoke alarm switches on when the count rate falls to 80 counts per second.

Explain why the radiation source inside the smoke alarm should have a long half-life.

Figure 11 shows a patient who has been injected with a radioactive source for medical diagnosis.

Figure 11

Explain the ideal properties of a radioactive source for use in medical diagnosis.