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Year 11
OCR
Foundation

Radioactive half-life

I can describe the random nature of radioactive decay and the predictability of radioactive half-life.

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New
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Year 11
OCR
Foundation

Radioactive half-life

I can describe the random nature of radioactive decay and the predictability of radioactive half-life.

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Lesson details

Key learning points

  1. Radioactive decay is a random process.
  2. It is impossible to predict the moment that a particular unstable nucleus will decay.
  3. It is possible to predict how long it will take for half of a sample of a radioactive isotope to decay.
  4. Radioactive half-life is the time taken for half of a radioactive isotope to decay (or for its activity to halve).
  5. Each radioactive isotope has its own half-life that is always the same.

Keywords

  • Random - to happen entirely by chance

  • Radioactive decay - a random process by which unstable nuclei emit radiation

  • Decay curve - shows the pattern in radioactive decay for a large set of identical unstable nuclei

  • Radioactive half-life - the time taken for half the nuclei of a radioactive isotope to decay

Common misconception

Most pupils have difficulty in truly understanding randomness.

Use analogies to explain randomness.

If the relevant health and safety rules are followed, midget gems are good for making half-life graphs. The sweets are eaten if they land on a flat side and are eaten - decaying into another substance. Different brands have different half-lives.
Teacher tip

Equipment

Large number of 6 sides dice, tray, optional: 8 sides dice to compare.

Content guidance

  • Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
Which of the following describe what a radioactive isotope is?
An atom with a stable nucleus that does not change over time.
Correct answer: An atom with an unstable nucleus that changes over time.
An atom that does not emit any radiation and remains unchanged.
Correct answer: An atom with an unstable nucleus that emits radiation.
Q2.
What happens to a nucleus when it undergoes radioactive decay?
It only emits energy.
It only emits particles.
Correct answer: It can emit energy or particles or both.
It splits into two smaller nuclei.
Correct answer: It transforms into the nucleus of a different element or isotope.
Q3.
Radioactive decay is the process where …
a larger nucleus splits into two smaller nuclei.
an atom loses its outer shell electrons to form an ion.
Correct answer: an unstable nucleus emits radiation to become more stable.
two smaller nuclei combine to form a larger nucleus.
Q4.
Which of the following methods can an unstable nucleus use to decay?
alpha decay
beta decay
gamma decay
Correct answer: all of the above
Q5.
Which of the following are random events?
Correct answer: Tossing a coin.
Correct answer: Rolling a pair of dice.
The temperature at which pure ice melts.
Correct answer: Picking a card out of a shuffled deck.
The temperature at which pure water boils.
Q6.
The decay of a radioactive isotope is a random process. This means that we cannot predict …
Correct answer: which unstable nucleus will decay next.
which element an unstable nucleus will decay into.
Correct answer: when an unstable nucleus will decay.
which type of radiation an unstable nucleus will emit.

Exit quiz

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6 Questions

Q1.
Which of the following definitions describing the half–life of a radioactive isotope is correct?
Half the time it takes for one nucleus to decay.
Correct answer: The time it takes for half of all the nuclei to decay.
Half the time it takes for the number of nuclei to fall to zero.
Q2.
Which of the following factors affects the half–life of a radioactive substance?
the temperature of the environment
the pressure of the environment
the chemical form of the substance
Correct answer: the type of radioactive isotope
Q3.
Which of the following statements about the half–life of radioactive isotopes are correct?
Correct answer: The half–life of a particular radioactive isotope is constant.
Half–life does not depend on the radioactive isotope.
Correct answer: Half–life is a property unique to each radioactive isotope.
All radioactive isotopes have the same half–life.
Correct answer: Half–life values vary greatly between different isotopes.
Q4.
Starting with the shortest, sort the following radioactive isotopes into order of increasing half-life.
1 - thorium–217: half–life = 1 millisecond
2 - californium–239: half–life = 1 minute
3 - dubnium–270: half–life = 1 hour
4 - ruthenium–106: half–life = 1 year
5 - carbon–14: half–life = 5730 years
6 - uranium–238: half–life = 4.5 billion years
Q5.
Two radioactive isotopes of uranium are uranium–235 (U–235) and uranium–238 (U–238). Which of the following statements about their half–lives is correct?
U–238 and U–235 have the same half–life.
U–238 has a much shorter half–life than U–235.
Correct answer: U–238 and U–235 have different half–lives because they are different isotopes.
The half–life of each depends on chemical properties, not nuclear properties.
Q6.
A radioactive isotope has a half–life of 5 minutes. Match each of the following amounts of the sample remaining to the correct amount of time that has passed.
Correct Answer:100%,0 mins

0 mins

Correct Answer:50%,5 mins

5 mins

Correct Answer:25%,10 mins

10 mins

Correct Answer:12.5%,15 mins

15 mins

Correct Answer:6.25%,20 mins

20 mins