Half-life

There are different isotopes of the element lead.

What is the difference between the atoms of different isotopes of lead?

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The isotope lead-210 is radioactive.

What is meant by ‘lead-210 is radioactive’?

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The isotope lead-210 emits beta radiation.

What is beta radiation?

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The paint in an old painting contains the isotope lead-210.

The lead-210 in the paint can be used to estimate the age of the painting.

Figure 1 shows how the activity of the lead-210 in the paint changes with time.

What was the initial activity of the lead-210 in the paint?

Use Figure 1.

Calculate the activity of the lead-210 in the paint after one half-life.

What was the estimated age of the painting when the activity was 10 kBq?

Use Figure 1.

The paint also contains other radioactive substances.

A scientist removed the other radioactive substances before measuring the activity.

The activity would be greater if the other radioactive substances were not removed.

How would the estimate of the age of the painting be different if the activity was greater?

Use Figure 1.

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The other radioactive substances in the paint emit different types of radiation.

Complete the sentence.

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Complete the sentence.

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Some people used to think that radioactive substances had health benefits.

100 years ago, a company made toothpaste containing the radioactive isotopes radium-228 and radium-226.

Figure 3 shows the symbols for these isotopes.

How are atoms of radium-228 different from atoms of radium-226?

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Figure 4 shows how the activity of a sample of radium-228 changed over time.

What is the approximate half-life of radium-228?

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A scientist investigated whether the toothpaste in four tubes of the 100-year-old

toothpaste is equally radioactive.

Figure 5 shows the equipment used.

When the equipment was arranged as shown in Figure 5, it was not possible to detect alpha particles from the toothpaste.

Suggest how the scientist adjusted the equipment to detect alpha particles from the toothpaste.

The scientist adjusted the equipment and determined the activity of the toothpaste from each tube.

Table 1 shows the results.

What was the range of activities shown in Table 1 ?

What was the independent variable in the investigation?

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What was the dependent variable in the investigation?

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When the toothpaste was new, it caused a risk to health because of the nuclear radiation emitted.

What happened to the risk to health from the toothpaste after 100 years?

Which property makes nuclear radiation hazardous?

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Some people used to think that radioactive substances had health benefits.

In the 1920s, a water container called a revigator was sold.

The walls of a revigator contain radioactive isotopes.

Figure 6 shows a revigator.

The revigator was filled with water and left overnight.

People then drank the water from the revigator.

The water was irradiated and contaminated by the radioactive isotopes in the walls of the revigator.

Explain how irradiating and contaminating the water affected the hazard caused by drinking the water.

A scientist tested some water that had been left in a revigator.

The water contained radon-222 and vanadium-52.

Vanadium-52 (V) decays by emitting beta particles.

What is the correct nuclear equation for this process?

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Table 2 shows the half-lives of radon-222 and vanadium-52.

The scientist measured the radiation emitted by a sample of radon-222 and the radiation emitted by a sample of vanadium-52.

The scientist repeated the measurements 7.4 minutes later.

Explain how the activity of the radon-222 and vanadium-52 had changed after 7.4 minutes.

Scientists monitored the effects of drinking the water from a revigator.

Their methods and results were checked by other scientists.

What name is given to the process of other scientists checking work before it is published?

A scientist investigated the radiation emitted by different radioactive isotopes.

The scientist had a sample of polonium-210.

The radiation emitted by polonium-210 can be represented by the symbol⁴₂ He.

Which type of radiation can be represented by the symbol⁴₂ He?

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How many protons are there in a particle of radiation represented by⁴₂ He?

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A polonium-210 (Po) nucleus changes into a lead (Pb) nucleus by emitting a ⁴₂ He particle. This is shown by the following nuclear equation. 210 206 4 Po → Pb + He 84 X 2

What is the value of X ?

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The sample of polonium-210 had an activity of 100 Bq.

Complete the sentence.

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After one half-life, the activity of polonium-210 in the sample

The scientist investigated another radioactive isotope that is a source of gamma

radiation.

Figure 1 shows the equipment used.

The count-rate is the number of counts detected each second.

In 30 seconds the number of counts detected was 1500.

Calculate the count-rate.

The scientist placed a thick sheet of lead between the source of gamma radiation and

the detector.

What was the effect of the sheet of lead on the count-rate?

Give a reason for your answer.

The lead was irradiated by the gamma radiation.

What happened to the lead when it was irradiated by the gamma radiation?

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Gamma radiation is emitted from the nucleus of an atom.

Complete the sentence.

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Gamma radiation consists of.

Figure 2 shows the scientist holding the radioactive source using tongs.

Suggest one reason why using long tongs rather than short tongs was safer for the scientist.

A scientist investigated a sample of a radioactive material to determine if it would be suitable for medical use.

The method, results and conclusions of the scientist will need to be checked by other scientists before the results of the investigation are published. What name is given to this checking process?

There is an increased risk of cancer if the scientist is irradiated by nuclear radiation. What property of nuclear radiation causes the increased risk of cancer?

The activity of a radioactive source is the rate at which the nuclei of the source decay. What is the unit for the activity of a radioactive source?

The scientist placed a radiation detector near the sample and measured the count-rate. Explain why the count-rate is less than the activity of the sample.

The scientist recorded the count-rate from the sample with the radiation detector at different distances from the sample. Table 2 shows the results.

Explain which type of radiation was emitted by the sample.

The scientist moved the detector closer to the sample and started a stopwatch. The scientist measured the count-rate from the sample at different times. Table 3 shows some of the results.

The scientist realised that 30 minutes is a whole number of half-lives. Calculate the value of X in Table 3.

The scientist had a second sample of the radioactive material. The scientist made appropriate measurements, then calculated the half-life of each sample. Why was the half-life calculated from the second sample slightly different from the half-life calculated from the first sample? Tick (✓) one box.

A smoke detector contains a source of alpha radiation in a plastic case.

A source of beta radiation in a smoke detector would be more hazardous than a source of alpha radiation. Explain why.

Actinium (Ac) is one source of alpha radiation. An actinium (Ac) nucleus emits an alpha particle (α) and turns into a francium (Fr) nucleus. This can be represented as:

Determine the values of A and Z.

A teacher wanted to find out what nuclear radiation is emitted from a source. The teacher placed different barriers between the source and a detector. The teacher recorded the count for 30 seconds after each barrier was put in place. Table 2 shows the results.

Explain what nuclear radiation was emitted by the source.

Figure 11 shows how the activity of four different radioactive isotopes, A, B, C and D changes over time.

Write the isotopes A, B, C and D in order of increasing stability of their nuclei. Explain your answer.

Least stable Most stable

Between 1951 and 1992 the USA tested nuclear weapons in a desert.

Complete the sentence. Choose the answer from the box.

Radioactive dust from the nuclear weapons testing settled on the desert. This is

The desert now contains radioactive tritium. Figure 3 shows how the activity of the tritium in a sample taken from the desert changed with time.

The sample was collected from the desert in 1992. Determine the activity of the tritium in the sample in 2007.

How much time did it take for the activity of the tritium in the sample to decrease from 80 Bq to 40 Bq?

What is the half-life of tritium?

The sample started with 45 billion atoms of tritium. After 4 years the sample had 36 billion atoms of tritium. Calculate the percentage of the tritium in the sample that remained after 4 years.

A scientist determined the activity of a sample of tritium every minute for 3 minutes. Table 1 shows the results.

Why do the activity readings in Table 1 vary? Tick (✓) one box.

What safety precaution should scientists take when working with radioactive materials in a laboratory? Tick (✓) one box.

Studies show that children born near the area of the desert containing tritium were more likely to develop cancer. It is important that the results from these studies are checked by other scientists. What is this process called? Tick (✓) one box.

A student modelled radioactive decay by rolling some dice in a tray. Dice that landed on the number six were removed from the tray. The removed dice represent nuclei that have decayed.

Why is rolling dice a suitable model for radioactive decay?

The student rolled 144 dice and removed all those that landed on the number six. The student rolled the remaining dice and again removed all those that landed on the number six. When the student had rolled the dice 20 times there were 9 dice left. Calculate the most likely number of times that the student had rolled the dice before the number of dice had halved. You should show how you work out your answer.

The number of times the dice have to be rolled to halve the original number of dice in the tray represents the half-life. Figure 7 shows an eight-sided dice and a six-sided dice.

The student now used eight-sided dice to model radioactive decay. Dice that landed on the number six were again removed from the tray. The half-life represented by rolling eight-sided dice is likely to be different from the half-life represented by rolling six-sided dice. Explain how.

A teacher has two radioactive sources, A and B. Source A has a longer half-life than source B. What can be deduced about the nuclei in source A compared with the nuclei in source B ? Do not refer to isotopes in your answer.

Protactinium (Pa) is radioactive.

An atom of one isotope of protactinium contains 91 protons and 143 neutrons.

What is the correct symbol for this atom?

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A teacher investigated how the count rate from a sample of protactinium changed over time.

Table 2 shows the results.

Figure 6 shows some of the teacher’s results.

Complete the graph in Figure 6.

Use data from Table 2.

Draw the line of best fit.

How much time did it take for the count rate to change from 200 counts per second to 100 counts per second?

What is the half-life of protactinium?

The nuclear radiation from the protactinium can pass through paper.

This radiation can only be detected up to 1 metre away from the protactinium.

What type of radiation is emitted by the protactinium?

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The teacher read an article about the effects of radiation on the human body.

Why are articles in scientific journals generally more trustworthy than articles in newspapers?

Lanthanum-140 is a radioactive isotope.

A nucleus of lanthanum-140 emits gamma radiation. What happens to the mass number and the charge of the nucleus when

Why is it difficult to detect gamma radiation?

Activity is the rate at which a radioactive source decays. A teacher measured the count-rate from a sample of lanthanum-140 using a Geiger-Muller (G-M) tube. Explain why the count rate was less than the activity of the sample of lanthanum-140

The teacher investigated how the thickness of lead affected the amount of gamma radiation that could pass through it. Figure 6 shows the apparatus.

Explain why the teacher stood as far away from the apparatus as possible.

Table 1 shows the results.

The teacher concluded that the count rate was not inversely proportional to the thickness of lead. Explain why the teacher was correct. Use the data in Table 1.

Lanthanum-140 can also emit beta radiation and change into cerium. Complete the equation showing the decay of lanthanum (La) 140 into cerium (Ce).

There are other isotopes of cerium which are radioactive. Different isotopes of cerium have different half-lives. The half-life of an isotope can be found by studying how the number of atoms changes over time. Figure 7 shows how the number of atoms of cerium-148 in a 120 g sample changes over time.

Determine the ratio of the number of cerium atoms in the sample when it was 100 seconds old compared with when the sample was 350 seconds old. Use data from Figure 7.

Determine the activity of the sample of cerium when the sample was 20 seconds old. Use Figure 7.

The Chernobyl disaster was a nuclear accident that happened in 1986 Radioactive isotopes were released into the environment. The radioactive isotopes emitted alpha, beta and gamma radiation.

What is an alpha particle? Tick one box.

Which statement about beta radiation is true? Tick one box.

Which statement about gamma radiation is true? Tick one box.

Table 3 shows the half-lives of two of the radioactive isotopes that contaminated the environment.

A soil sample was taken from the area around Chernobyl in 1986 The soil sample was contaminated with equal amounts of caesium–137 and iodine–131 Explain how the risk linked to each isotope has changed between 1986 and 2018 Both isotopes emit the same type of radiation.

Determine the year when the activity of the caesium–137 in the soil sample will be 1/32 of its original value.