a random process by which unstable nuclei emit radiation

shows the pattern in radioactive decay for a large set of identical unstable nuclei

the time taken for half the nuclei of a radioactive isotope to decay

Radioactive half-life

Combined science

In A-level physics, some pupils will build on this knowledge to learn about probability and half-life equations, nuclear instability, Einstein’s equation E = mc2 that links mass and energy, and controlled nuclear fission.

In the Periodic table unit, in chemistry, pupils learnt about the nuclear model of the atom, the atomic number and mass number, and about isotopes of elements.

Nuclear physics

Physical activity and equipment requiring safe use

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.

Which of the following definitions describing the half–life of a radioactive isotope is correct?

Which of the following factors affects the half–life of a radioactive substance?

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.

Which of the following statements about the half–life of radioactive isotopes are correct?

thorium–217: half–life = 1 millisecond

californium–239: half–life = 1 minute

uranium–238: half–life = 4.5 billion years

Starting with the shortest, sort the following radioactive isotopes into order of increasing half-life.

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.

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?

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.

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. 

Which of the following describe what a radioactive isotope is?

It transforms into the nucleus of a different element or isotope.

What happens to a nucleus when it undergoes radioactive decay?

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.

Radioactive decay is the process where …

Which of the following methods can an unstable nucleus use to decay?

The temperature at which pure water boils.

Which of the following are random events? 

which element an unstable nucleus will decay into.

which type of radiation an unstable nucleus will emit.

The decay of a radioactive isotope is a random process. This means that we cannot predict …

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Radioactive half-life

Lesson outcome

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