Half-life

Figure 6 shows a diagram of a helium atom.

Complete the table for particles G and H, as shown in Figure 6.

An atom of beryllium has the symbol

Be 9 4

The beryllium atom has 4 protons.

Determine the number of neutrons in this atom.

Determine the number of electrons in this atom.

Which of these is the unit for the activity of a radioactive isotope?

The isotope nitrogen-13 (N-13) has a half-life of 10 minutes.

A sample of N-13 has an initial mass of 120 g.

Calculate the mass of N-13 that remains after 30 minutes.

mass remaining =_........

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.).

Carbon-14 is a radioactive substance that emits beta minus (β^–) particles.

Which of these is the unit for the activity of a sample of carbon-14?

Which row of the table gives a correct comparison of the penetrating abilities of alpha, beta and gamma radiation?

The mass of a beta minus particle is 9.1 × 10^–31kg.

Calculate the kinetic energy of a beta minus particle moving with a speed of 3.8 × 10⁶m / s.

kinetic energy =_........

Describe what happens in the nucleus of an atom when a beta plus particle is emitted.

*(c) Radioactive decay can produce gamma radiation and alpha radiation.

Compare the processes of gamma decay and alpha decay.

Your answer should include

• a description of both gamma radiation and alpha radiation

• the effect of each type of decay on the original nucleus.

Radiation is used to treat tumours (cancer).

The source of the radiation can be inside or outside the human body.

Which of these has a radiation source that can be positioned inside the body to treat tumours?

Figure 22 shows a PET scanner used to detect cancerous tumours.

A radioactive isotope is injected into a patient.

The isotope is absorbed by the tumour.

The isotope emits positrons from the location of the tumour.

The ring of radiation detectors rotates around the person.

Explain how the scan can give the location of the tumour.

Explain why the radioactive isotope injected into the patient must be produced near to the place where it is to be used.

Radiotherapy can involve irradiation of patients.

Radioactive tracers can involve contamination of patients.

State two differences between irradiation and radioactive contamination.

Figure 23 shows the decay curves of two different isotopes, Q and P.

Use the graph in Figure 23 to determine the half-life of isotope P.

Suggest a reason why the sample of isotope Q could be more dangerous to humans than the sample of isotope P.

Radiation is used to treat tumours (cancer).

The source of the radiation can be inside or outside the human body.

Which of these has a radiation source that can be positioned inside the body to treat tumours?

Figure 5 shows a PET scanner used to detect cancerous tumours.

A radioactive isotope is injected into a patient.

The isotope is absorbed by the tumour.

The isotope emits positrons from the location of the tumour.

The ring of radiation detectors rotates around the person.

Explain how the scan can give the location of the tumour.

Explain why the radioactive isotope injected into the patient must be produced near to the place where it is to be used.

Radiotherapy can involve irradiation of patients.

Radioactive tracers can involve contamination of patients.

State two differences between irradiation and radioactive contamination.

Figure 6 shows the decay curves of two different isotopes, Q and P.

Use the graph in Figure 6 to determine the half-life of isotope P.

Suggest a reason why the sample of isotope Q could be more dangerous to humans than the sample of isotope P.

An atom has a central nucleus containing neutrons and protons.

Electrons orbit the nucleus.

Which row of the table gives the relative mass and charge of a proton?

An atom has a radius of 1.0 × 10^–10m.

A nucleus has a radius of 1.0 × 10^–15m.

Calculate the ratio of the radius of the atom to the radius of the nucleus.

Explain why an atom has no charge overall.

State the number of protons in one atom of carbon-14.

State the number of neutrons in one atom of carbon-14.

Figure 6 shows a graph for the decay of the radioactive isotope carbon-14.

Use the graph to estimate the half-life of carbon-14.

Figure 11 is the symbol for a nucleus of americium-241.

Figure 11

Americium-241 is a radioactive isotope of americium.

Americium-241 decays by emitting alpha (α) particles.

Which of these is the symbol for another radioactive isotope of americium?

Which of these is the approximate maximum distance that alpha particles can travel in air at normal atmospheric pressure?

Complete the equation in Figure 12 for americium-241 decaying into neptunium (Np).

Figure 12

The activity of a radioactive source is measured as 128 Bq.

This is shown as a point on the graph in Figure 13.

The half-life of this radioactive source is 17 s.

Use this information to plot three more points on the graph grid in Figure 13 to show how the activity of the source changes with time.

Describe what happens in the nucleus of an atom when a positron is emitted.

Figure 10 shows a safety sign on the door of a laboratory where radioactive materials are used.

State one way that radioactivity can be dangerous to humans.

State one piece of equipment that can be used to measure radioactivity.

Alpha (α) radiation and ultraviolet (UV) radiation are ionising radiations.

Give two other ionising radiations.

Sulfur‑35 is a radioactive isotope of sulfur.

Figure 11 represents a nucleus of sulfur‑35.

35 S 16

Figure 11

Draw one line from each type of particle to the number of that type of particle in a nucleus of sulfur‑35.

A sample of a radioactive isotope has a mass of 520 g.

The half‑life of the radioactive isotope is 18 days.

Calculate the mass of the original radioactive isotope remaining after 18 days.

mass after 18 days_........

Calculate the mass of the original radioactive isotope remaining after 54 days.

mass after 54 days_........

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

This question is about radioactivity.

Alpha (α), beta (β) and gamma (γ) are three types of radioactive emissions.

Which statement describes all of these radioactive emissions?

Fluorine-19 is a stable isotope of the element fluorine.

The element fluorine also has several radioactive isotopes.

Describe one similarity and one difference between the numbers of particles in one nucleus of fluorine-19 and one nucleus of a radioactive isotope of fluorine.

Figure 14 shows a Geiger-Muller (G-M) tube attached to a counter. The G-M tube is used to measure the activity of a source of beta (β) radiation. There is an aluminium sheet between the beta source and the G-M tube. The counter is switched on and after 1 minute shows a count of 268.

The aluminium sheet is taken away. The counter is reset to zero and then switched on again. A new count is taken for 1 minute.

Explain why the new count is greater than 268.

The beta source is then also taken away. The counter is reset to zero and switched on again. A new count is taken for 1 minute.

Give a reason why there would now be a reading on the counter.

State the SI unit for the activity of a radioactive source.

*(d) Exposing people to radioactive sources can be dangerous.

Describe the dangers of exposure to radioactive sources and what can be done to protect hospital staff when they are working with radioactive sources.

This question is about radioactivity.

Alpha (α), beta (β) and gamma (γ) are three types of radioactive emissions.

Which statement describes all of these radioactive emissions?

Fluorine-19 is a stable isotope of the element fluorine.

The element fluorine also has several radioactive isotopes.

Describe one similarity and one difference between the numbers of particles in one nucleus of fluorine-19 and one nucleus of a radioactive isotope of fluorine.

Figure 3 shows a Geiger-Muller (G-M) tube attached to a counter. The G-M tube is used to measure the activity of a source of beta (β) radiation. There is an aluminium sheet between the beta source and the G-M tube. The counter is switched on and after 1 minute shows a count of 268.

The aluminium sheet is taken away. The counter is reset to zero and then switched on again. A new count is taken for 1 minute.

Explain why the new count is greater than 268.

The beta source is then also taken away. The counter is reset to zero and switched on again. A new count is taken for 1 minute.

Give a reason why there would now be a reading on the counter.

State the SI unit for the activity of a radioactive source.

Radium-223 is a radioactive substance.

Radium-223 is an alpha emitter.

The half-life of radium-223 is 11 days.

A radioactive source contains 1.7 × 10²³ nuclei of radium-223.

Calculate the number of radium-223 nuclei remaining in the source after a time of 33 days.

Figure 8 shows the symbol for the nucleus of an atom of strontium‑90.

Sr 90 38

Figure 8

How many protons are in the nucleus of an atom of strontium‑90?

How many neutrons are in the nucleus of an atom of strontium‑90?

The half‑life of strontium‑90 is 29 years.

The table in Figure 9 gives some information about how the mass of a sample of strontium‑90 changes with time.

Complete the table in Figure 9.

A teacher sets up an experiment to show some students how far beta particles travel in air.

Figure 10 shows some of the equipment she uses.

State the scientific name for the radioactivity detector shown in Figure 10.

The teacher also has:

• a radioactive source that emits only beta particles

• a metre rule.

State two precautions the teacher must take to protect herself from the effects of radioactivity.

Describe how the teacher could show how far beta particles travel in air.

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.

Which of these describes isotopes of an element?

Figure 9 represents a decay that can happen inside the nucleus of an atom.

Which decay is represented in Figure 9?

The half-life of cobalt-60 is 5 years.

A school cobalt source had an activity of 38.5 kBq in the year 2000.

Estimate the activity of this source in the year 2020.

Explain what can happen to the body if a person has a prolonged exposure to gamma rays.

A G-M tube is connected to a counter. A teacher places the G-M tube near to a radioactive source. A student starts the counter and clock at the same time and writes down the readings shown on the counter every 15 s.

The student plots the readings with a line of best fit, as shown in Figure 10.

Calculate the average count rate, in counts / s, from the graph.

Show your working on the graph.

average count rate =_........ counts / s

The student says that the experiment must have been done carelessly because the data seemed quite scattered away from the best fit line.

The teacher claims such results should be expected in radioactivity experiments.

Justify the teacher’s claim.

Carbon‑13 and carbon‑14 are isotopes of carbon.

Nuclei of carbon‑13 and carbon‑14 can be represented by these symbols

13 14

Complete the table for an atom of carbon‑13 and an atom of carbon‑14.

State the name of an instrument that can be used to measure radioactivity.

State two sources of background radiation.

Carbon‑14 is radioactive and has a half‑life of 5 700 years.

The number of radioactive carbon‑14 atoms in a very old piece of wood is found to have decreased from 1 000 000 to 125 000.

Determine the age of the piece of wood.

Carbon‑14 decays into nitrogen‑14.

The symbol for nitrogen‑14 is¹⁴₇N

Explain what happens in a carbon‑14 nucleus when it decays to a nitrogen‑14 nucleus.

Figure 17 shows a Geiger‑Müller (GM) tube used for measuring radioactivity.

Describe how a teacher should use a Geiger‑Müller (GM) tube to compare the count‑rates from two different radioactive rocks.

A hospital uses a radioactive isotope with a half‑life of 6 hours.

A technician measures a count rate of 80 counts per minute (cpm) from this isotope.

Complete the graph on Figure 18, as accurately as possible, to show how the count‑rate from this isotope will change from the time of the first measurement.

The first point is already drawn in Figure 18.

*(c) A radioactive rock is placed near to the front of a Geiger‑Müller (GM) tube.

A radioactivity count‑rate is first made in air.

The count‑rate is measured again with each of three different absorbers between the rock and the GM tube.

Figure 19 shows the count‑rates measured.

A scientist has an idea that the rock emits three different types of radiation.

Explain how the data in this table supports the scientist’s idea.

Figure 4 shows a Geiger-Müller (GM) tube used for measuring radioactivity.

Figure 4

Describe how a teacher should use a Geiger-Müller (GM) tube to compare the count-rates from two different radioactive rocks.

A hospital uses a radioactive isotope with a half-life of 6 hours.

A technician measures a count rate of 80 counts per minute (cpm) from this isotope.

Complete the graph on Figure 5, as accurately as possible, to show how the count-rate from this isotope will change from the time of the first measurement.

The first point is already drawn in Figure 5.

One radioactive source used in hospitals is technetium (Tc).

Technetium is produced from the radioactive decay of molybdenum (Mo).

Complete the following nuclear equation.