Physics (AS & A Level) · Feb / March 2016 · Paper 42 · Question 13
9702
As printed in the paper
The question as text
Beryllium-7 (7 4 Be) is produced in the upper atmosphere and then sinks down onto the Earth’s surface. Nuclei of beryllium-7 decay with a half-life of 53.3 days to form stable nuclei. The activity of a sample of beryllium-7 on a tree leaf is 39 mBq. 7 1
Read automatically from the paper; the printed page above is exact.
Show the answer and mark scheme
13(a)[1]
λ = ln2 / T½ = ln2 / (53.3 × 24 × 60 × 60) =1.5 × 10–7 s–1 [1]
13(b)[3]
A = λN N = 39 × 10–3 / 1.5 × 10–7 = 2.6 ×105 m = (2.6 × 105 / 6.0 × 1023) × 7 × 10–3 or 2.6 × 105 × 1.66 × 10–27 × 7 = 3.0 × 10–21 kg [3]
13(c)[2]
2 / 39 = exp (–1.5 × 10–7 × t) or 2 / 39 = (1 / 2)[t / (53.3 × 24 × 3600)] t = 2.0 × 107 s [2]
Make a free account to save your answers and see your weak topics and ask the AI why a wrong answer is wrong.