Physics 9702 · AS & A Level · Radioactive decay

Radioactive decay — practice question

(a(i))[1]

A sample of a radioactive isotope is described as having random and spontaneous decay. Explain what is meant by the decay being random.

(a(ii))[1]

A sample of a radioactive isotope is described as having random and spontaneous decay. Explain what is meant by the decay being spontaneous.

(b)[3]

A radioactive isotope X has a half-life of $1.4\ \text{hours}$. A pure sample of isotope X starts with an activity of $3.6 \times 10^5\ \text{Bq}$. Determine the activity of isotope X in the sample after $2.0\ \text{hours}$.

(c(i))[1]

The variation with time $t$ of the actual activity $A$ of the sample in (b) is shown in Fig. 12.1. The initial activity of isotope X in the sample is $3.6 \times 10^5\ \text{Bq}$. Use information from (b) to sketch, on the axes of Fig. 12.1, how the activity of a pure sample of isotope X varies with time $t$.

(c(ii))[2]

Suggest a reason for any difference between the actual activity of the sample in Fig. 12.1 and the curve you have drawn for the activity of isotope X.

Worked solution & mark scheme

This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: decay time cannot be predicted / constant chance of decay

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