Half-life

A protactinium generator is a device that can produce samples of an isotope called protactinium‑234m.

A teacher investigates the activity of protactinium‑234m using the apparatus shown in the photograph.

The teacher uses a radiation detector to detect the radiation emitted from the protactinium‑234m.

Give the name of a suitable radiation detector.

Give two safety precautions to minimise the risk of harm to the teacher from the radiation emitted by the protactinium generator.

Protactinium‑234m decays with a half‑life of 70 seconds.

The initial count rate is 840 counts per second.

Calculate the expected count rate after 140 seconds.

count rate =_........ counts per second

The activity of an isotope is the total amount of radiation emitted each second.

The teacher estimates that only 5% of the total radiation emitted is detected by the radiation detector.

Estimate the activity of the isotope when the count rate is 840 counts per second.

Give the unit.

Uranium‑239 is an isotope of the element uranium.

State what is meant by the term isotopes.

Uranium‑239 can be represented using the symbol

Protons are one type of particle found in the nucleus of an atom.

How many protons are in the nucleus of an atom of uranium‑239?

Give the name of the other particle found in the nucleus of an atom of uranium‑239.

Uranium‑239 is radioactive and decays by beta emission.

Uranium‑239 has a half‑life of 23 minutes.

A sample of uranium‑239 has an initial mass of 60 g.

Calculate the mass of uranium‑239 remaining after 46 minutes.

When uranium‑239 undergoes beta decay, an isotope of the element neptunium, Np, is produced.

Which of these is the correct symbol for the neptunium nucleus produced in the beta decay of uranium‑239?

A teacher investigates a sample of radioactive material.

The graph shows their results.

On the graph, give the unit for activity.

Describe what is meant by the term background radiation.

Describe what is meant by the term half‑life.

Use the graph to determine the half‑life of this radioactive sample.

half‑life =_........ minutes

The teacher suggests that this formula shows the relationship between activity and time taken.

activitytime taken = constant

Use data from the graph to determine if this relationship is correct.

This question is about radioactivity.

The nucleus of an atom of carbon has 6 protons and 8 neutrons.

Which row of the table shows the nucleus of an atom that is a different isotope of carbon?

Which type of radiation is a high-energy electron?

A nucleus emits radiation. This causes the mass number to decrease by one. The atomic number stays the same.

Which type of radiation does the nucleus emit?

The nucleus of an isotope of uranium can be represented using this symbol.

The nucleus forms part of a positively charged ion.

How many electrons could be in this ion?

A radioactive isotope has an initial activity of 400 Bq.

The half-life of the isotope is 8 hours.

What is the activity of the isotope after 16 hours?

This question is about radioactive isotopes used for medical imaging.

How many neutrons are in the nucleus of an atom of iodine-131?

Iodine-131 is radioactive and decays with a half-life of 8 days.

State what is meant by the term half-life.

The cross () on the graph shows the initial number of atoms in a sample of iodine-131.

Draw three more crosses () on the graph to show how the number of atoms of iodine-131 in the sample changes during three half-lives.

[iodine-131 half-life = 8 days]

Use a curve of best fit on the graph to estimate the time taken for the number of atoms in the sample to decrease to 5000.

When iodine-131 decays, it emits beta radiation and gamma radiation.

A patient swallows a tablet containing iodine-131. The radiation emitted can be detected outside the body.

State the name of a piece of equipment that can detect the radiation emitted by iodine-131.

Give a reason why gamma radiation is more likely to be detected outside the body than beta radiation.

Technetium-99m is another radioactive isotope.

Iodine-131 and technetium-99m are both used as medical tracers. Medical tracers use radiation detected outside the body to diagnose illnesses.

The table gives information about some of the properties of iodine-131 and technetium-99m when they undergo radioactive decay.

Explain why technetium-99m is likely to be safer than iodine-131 when used as a medical tracer.

This question is about using carbon dating to find the age of pieces of wood.

The equation shows how carbon-14 forms in the atmosphere.

State the name of particle X.

Carbon-14 decays by beta decay.

State what happens to the number of protons and the number of neutrons in a carbon-14 nucleus when it decays.

A scientist determines how the percentage of carbon-14 remaining in a sample of wood changes with time.

The table shows the scientist’s data.

Plot the scientist’s data on the grid.

Draw the curve of best fit.

Use the graph to determine the age of a sample of wood that has 36% of its carbon-14 remaining.

Carbon-14 dating is inaccurate for samples of wood produced after 1950.

This is because the concentration of carbon-14 in the atmosphere greatly increased due to nuclear weapons testing.

A tree absorbs carbon-14 during its lifetime.

A student suggests that trees grown after 1950 are contaminated with carbon-14.

Give a reason why the student’s suggestion is correct.

Explain how nuclear weapons testing affects the determination of the age of a sample of wood produced after 1950.

This is a question about radioactivity.

Which of these is the unit of activity?

Which of these is the correct description of the term half-life ?

A teacher demonstrates how the activity of a radioactive sample changes with time.

The box gives the names of different pieces of equipment.

Complete the sentences using words from the box.

The teacher measures time with a_........ .

The teacher measures the count rate with a_........ and a counter.

The graph shows the teacher’s results.

Draw a circle around the anomalous result.

Use the graph to determine the half-life of the radioactive sample.

Give a reason why the teacher should not expect the data points to lie exactly on the curve of best fit.

Protactinium is an element with several different radioactive isotopes.

Protactinium‑234 has a half‑life of 6.7 hours.

A sample of protactinium‑234 has an initial activity of 800 units.

Give a suitable unit for activity.

On the axes below, sketch a graph for the decay of the sample of protactinium‑234 during its first three half‑lives.

When protactinium‑234 undergoes beta (β^–) decay it becomes uranium‑234.

The incomplete nuclear equation shows this process.

Complete the nuclear equation to show the beta decay of protactinium‑234.

Write your answers in the dashed boxes.

A student suggests an experiment to determine the type of radiation emitted by a different isotope of protactinium, protactinium‑231.

This is the suggested method.

Step 1 connect a suitable radiation detector to a radiation counter

Step 2 place a source of protactinium‑231 at a fixed distance of 3 cm from the radiation detector

Step 3 record the count of detected radiation for a time of one minute

Step 4 place a sheet of paper between the source and detector

Step 5 record the count of detected radiation for a time of one minute

Step 6 repeat Steps 4 and 5 using a sheet of aluminium and then a sheet of lead instead of the sheet of paper

The table shows the results of the investigation when it is done by a teacher.

Which of these is the dependent variable in the investigation?

The student’s method does not allow for background radiation.

Describe how the student’s method should be modified to allow for background radiation.

Describe how the student’s method could be modified to improve the reliability of the results.

Evaluate the data from the experiment to conclude the type of radiation emitted by protactinium‑231.

The photograph shows the nuclear fusion reactor called ITER.

Describe the difference between nuclear fusion and nuclear fission.

At ITER, hydrogen-3 and hydrogen-2 will be fused into helium and another particle labelled X.

Complete the nuclear equation for the fusion of hydrogen-3 and hydrogen-2.

Discuss potential safety advantages of a fusion reactor compared with a fission reactor.

You should refer to the products of this fusion reaction and to the fission reaction of uranium.

The half-life of a radioactive isotope is 12 years.

The activity of a sample of this isotope is 120 kBq.

Calculate the activity of this sample after 48 years.

Which statement describes the term atomic number for a nucleus?

Which statement describes the term mass number for a nucleus?

Which statement describes the term isotopes ?

of protons

of electrons

of protons

of neutrons

An atom contains 8 protons, 8 neutrons and 8 electrons.

Which of these would result in a negatively charged ion of the same element?

It is not possible to predict exactly when a radioactive nucleus will decay.

Which feature of radioactive decay best explains this observation?

Which of these is the correct unit for measuring the activity of a radioactive sample?

Radon is a radioactive gas that contributes to background radiation.

Describe what is meant by the term background radiation.

The graph shows the activity of a sample of radon‑222.

State what is meant by the term half‑life.

Use the graph to determine the half‑life of radon‑222.

Radon‑222 is formed by multiple alpha decays of uranium‑234.

Complete the nuclear equation by giving the missing information.

Radon‑222 also emits alpha radiation.

Explain the hazard to humans of breathing in air contaminated with radon‑222.

A scientist wants to determine the half-life of a radioactive isotope.

The scientist measures the count rate from the radioactive isotope.

State how the scientist should correct the count rate for background radiation.

The graph shows how the activity of the radioactive isotope varies with time.

Explain what is meant by the term half-life.

Use the graph to determine the half-life of this isotope.

half-life =_........ minutes

Cobalt‑60 is a radioactive isotope of cobalt.

The table gives the activity of a sample of cobalt‑60 over a period of 10 years.

Give a suitable unit for activity.

The graph shows the data.

Label both axes.

Draw the curve of best fit.

Use the graph to determine the half‑life of cobalt‑60.

Estimate the time taken for the activity to decrease to of its initial value.

Cobalt‑60 decays by beta emission.

Describe what happens to the nucleus of a cobalt‑60 atom during beta decay.

Cobalt‑60 also emits gamma radiation.

Cobalt‑60 is produced in a nuclear reactor.

Discuss the hazards involved and the precautions taken when disposing of cobalt‑60.

A teacher uses a radioactive source containing atoms of the isotope radium-226.

Give a safety precaution that would reduce the teacher’s exposure to radiation when working with the radioactive source.

Radium-226 can be represented using the symbol

How many neutrons are in the nucleus of an atom of radium-226?

The teacher investigates the type of radiation emitted from the radioactive source.

Give the name of a piece of apparatus that detects ionising radiation.

The teacher finds that the radiation emitted from the radioactive source is not detected when the detector is more than 5 cm away from the source.

State the type of radiation emitted by the radioactive source.

The number of radium-226 atoms in the source decreases over time, with a half-life of 1600 years.

State what is meant by the term half-life.

The radioactive source contains 2.66 × 10²¹ atoms of radium-226.

Approximately how many atoms of radium-226 will remain in the source after 800 years?

Uranium-235 captures a neutron and undergoes nuclear fission in a chain reaction.

The equation shows a possible nuclear fission reaction.

Calculate x, the number of neutrons released by this fission reaction.

Describe what is meant by a chain reaction.

Iodine-129 is an isotope found in radioactive waste from nuclear power stations.

Iodine-129 has a half-life of approximately 15 million years.

A sample of iodine-129 has an activity of 72 kBq.

Show that the time required for the sample to have an activity less than 5 kBq is approximately 60 million years.

Some radioactive waste from nuclear power stations has a very long half-life.

Discuss precautions that must be taken when disposing of this radioactive waste.

A machine called the synchrocyclotron (SC) was designed to cause protons to move in a circular path using strong magnetic fields.

The SC used electromagnets to produce the strong magnetic fields.

Describe the construction of a simple electromagnet.

You may draw a diagram to support your answer.

The diagram shows a proton moving at velocity v in the magnetic field produced by the SC.

The direction of the magnetic field is into the page.

Using the left hand rule, determine the direction of the force acting on the proton due to the magnetic field.

The SC is surrounded by very thick concrete walls.

The radiation produced by the SC created atoms of radioactive barium-133 in the concrete walls.

Barium-133 has a half-life of 10.5 years.

State what is meant by the term half-life.

In 1990, the SC stopped being used at CERN, a research centre.

In 1990, the largest number of barium-133 atoms were found 40 cm deep in the concrete walls.

Since 2014, members of the public have been allowed to visit the SC at CERN.

Explain why the radioactive barium-133 in the concrete walls is not a risk to people visiting the SC.

Technetium-99m is an isotope of the element technetium.

Technetium-99m has a half-life of 6 hours.

A sample of technetium-99m has an initial activity of 160 Bq.

Complete the graph to show how the activity of this sample of technetium-99m changes over a period of 24 hours.

Technetium-99m has a half-life of 6 hours and can be used as a medical tracer.

It is injected into a patient’s blood and moves around the patient’s body.

Technetium-99m emits gamma radiation, which is used to locate the position of the tracer in the patient’s body.

Technetium-99m does not exist naturally.

Suggest why technetium-99m is usually made at the hospital where it is used.

Explain why technetium-99m is an effective isotope to use as a medical tracer.

The gamma radiation emitted by technetium-99m is potentially harmful to humans.

Discuss the risks of using technetium-99m to doctors and to patients.

The photograph shows a glass plate made from uranium glass.

Uranium oxide is used to give the glass a green colour.

State what information the numbers 92 and 238 give about the nucleus of this isotope of uranium.

Uranium‑238 decays by alpha emission.

Describe how the nucleus of a uranium‑238 atom changes as a result of alpha emission.

The table gives some information about the uranium glass plate.

Calculate the number of uranium‑238 atoms in the plate.

Uranium‑238 is an alpha emitter and has a half‑life of 4.5 billion years.

Explain why it is safe to eat food from the uranium glass plate.

Lead-210 is a radioactive isotope of lead and is represented using this symbol.

State what is meant by the term isotope.

How many protons are in the nucleus of lead-210?

A sample of lead-210 has an initial activity of 240 Bq.

After 66 years, the activity of the sample is 30 Bq.

Calculate the half-life of lead-210.