Starter quiz
- Which of the following describe what a radioactive isotope is?
- An atom with a stable nucleus that does not change over time.
- An atom with an unstable nucleus that changes over time. ✓
- An atom that does not emit any radiation and remains unchanged.
- An atom with an unstable nucleus that emits radiation. ✓
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- What happens to a nucleus when it undergoes radioactive decay?
- It only emits energy.
- It only emits particles.
- It can emit energy or particles or both. ✓
- It splits into two smaller nuclei.
- It transforms into the nucleus of a different element or isotope. ✓
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- 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.
- an unstable nucleus emits radiation to become more stable. ✓
- two smaller nuclei combine to form a larger nucleus.
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- Which of the following methods can an unstable nucleus use to decay?
- alpha decay
- beta decay
- gamma decay
- all of the above ✓
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- Which of the following are random events?
- Tossing a coin. ✓
- Rolling a pair of dice. ✓
- The temperature at which pure ice melts.
- Picking a card out of a shuffled deck. ✓
- The temperature at which pure water boils.
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- The decay of a radioactive isotope is a random process. This means that we cannot predict …
- which unstable nucleus will decay next. ✓
- which element an unstable nucleus will decay into.
- when an unstable nucleus will decay. ✓
- which type of radiation an unstable nucleus will emit.
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Exit quiz
- 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.
- 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.
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- 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
- the type of radioactive isotope ✓
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- Which of the following statements about the half–life of radioactive isotopes are correct?
- The half–life of a particular radioactive isotope is constant. ✓
- Half–life does not depend on the radioactive isotope.
- Half–life is a property unique to each radioactive isotope. ✓
- All radioactive isotopes have the same half–life.
- Half–life values vary greatly between different isotopes. ✓
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- 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
- 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.
- 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.
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- 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.
- 100%⇔0 mins ✓
- 50%⇔5 mins ✓
- 25%⇔10 mins ✓
- 12.5%⇔15 mins ✓
- 6.25%⇔20 mins ✓
Worksheet
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Lesson Details
Key learning points
- Radioactive decay is a random process.
- It is impossible to predict the moment that a particular unstable nucleus will decay.
- It is possible to predict how long it will take for half of a sample of a radioactive isotope to decay.
- Radioactive half-life is the time taken for half of a radioactive isotope to decay (or for its activity to halve).
- Each radioactive isotope has its own half-life that is always the same.
Common misconception
Most pupils have difficulty in truly understanding randomness.
Use analogies to explain randomness.
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
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