A-LevelPhysicsNuclear physics9702/43 · Oct/Nov 2018 · Q1210 Marks
State what is meant by radioactive decay. [3]
- (a)State what is meant by radioactive decay. [3][3]
- (b)(i)Use the gradient of the line in [Figure 12.1] to determine the activity, in Bq, of the sample at time t = 4.0 hours. Show your working. activity = ................................................. Bq [3][3]
- (b)(ii)Use your answer in (i) to show that the decay constant λ of the isotope is approximately 4 × 10⁻⁵ s⁻¹. [2][2]
- (c)A sample of a different radioactive isotope has an initial activity of 4.6 × 10³ Bq. The sample must be stored safely until its activity is reduced to 1.0 × 10³ Bq. The decay constant of the isotope is 5.5 × 10⁻⁷ s⁻¹. The decay products are not radioactive. Calculate the minimum time, in days, for which the sample must be stored. time = ................................................. days [3][3]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.
- [B1] unstable nucleus
- [B1] emission of particles/photons
- [B1] emission is spontaneous or (particles/radiation) are ionising
- [B1] tangent drawn and gradient calculation attempted
- [A2] activity = 1.3 × 10⁹ Bq
- [C1] A = λN
- [A1] λ = (1.3 × 10⁹)/(3.05 × 10¹⁰) = 4.3 × 10⁻⁵ s⁻¹ (≈ 4 × 10⁻⁵ s⁻¹)
- [C1] A = A₀e⁻λt
- [C1] 1.0 × 10³ = 4.6 × 10³ exp(-5.5 × 10⁻⁷ × t)
- [A1] t = 2.78 x 10⁶ s
- [A1] = 32 days
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