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Question 18M.2.HL.TZ1.6b.iii

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Date May 2018 Marks available [Maximum mark: 3] Reference code 18M.2.HL.TZ1.6b.iii
Level HL Paper 2 Time zone TZ1
Command term Determine Question number b.iii Adapted from N/A
b.iii.
[Maximum mark: 3]
18M.2.HL.TZ1.6b.iii

The radioactive nuclide beryllium-10 (Be-10) undergoes beta minus (β–) decay to form a stable boron (B) nuclide.

The initial number of nuclei in a pure sample of beryllium-10 is N0. The graph shows how the number of remaining beryllium nuclei in the sample varies with time.

(b.iii)

Beryllium-10 is used to investigate ice samples from Antarctica. A sample of ice initially contains 7.6 × 1011 atoms of beryllium-10. The present activity of the sample is 8.0 × 10−3 Bq.

Determine, in years, the age of the sample.

[3]

Markscheme

λ «= ln ⁡ 2 1.4 × 10 6 » = 4.95 × 10–7 «y–1»

rearranging of A = λN0e–λt to give –λt = ln  8.0 × 10 − 3 × 365 × 24 × 60 × 60 4.95 × 10 − 7 × 7.6 × 10 11  «= –0.400»

t =  − 0.400 − 4.95 × 10 − 7 = 8.1 × 10 5  «y»

 

 

Allow ECF from MP1

[3 marks]

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