Mass number, atomic number and isotopes

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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Scientists have used lasers to start a nuclear fusion reaction.

The scientists used the lasers to heat a small amount of an isotope of hydrogen.

Describe what is meant by ‘isotopes’ of an element.

Explain how nuclear fusion releases energy.

The fusion reaction releases large amounts of energy.

The fusion reaction takes place in a reactor.

Explain why the walls of the reactor should be made from a material with a very high specific heat capacity.

Nuclear fusion is safer than nuclear fission.

Nuclear fission can lead to an uncontrolled chain reaction.

Give one consequence of an uncontrolled chain reaction.

Some isotopes emit nuclear radiation.

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

Complete the sentences.

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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.

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.

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?