DP Physics (last assessment 2024)

Question 21M.2.HL.TZ2.a.ii

Date	May 2021	Marks available	[Maximum mark: 3]	Reference code	21M.2.HL.TZ2.a.ii
Level	HL	Paper	2	Time zone	TZ2
Command term	Calculate	Question number	a.ii	Adapted from	N/A

a.ii.

[Maximum mark: 3]

21M.2.HL.TZ2.a.ii

During electron capture, an atomic electron is captured by a proton in the nucleus. The stable nuclide thallium-205 ( ${}_{81}^{205}{Tl}$ ) can be formed when an unstable lead (Pb) nuclide captures an electron.

The unstable lead nuclide has a half-life of 15 × 10⁶ years. A sample initially contains 2.0 μmol of the lead nuclide. Calculate the number of thallium nuclei being formed each second 30 × 10⁶ years later.

[3]

Markscheme

calculates $λ = \frac{\ln 2}{15 \times 10^{6}} « = 4.62 \times 10^{- 8} {year}^{- 1} »$ ✓

calculates nuclei remaining $= 0.50 \times 10^{- 6} \times 6.0 \times 10^{23} « = 3.0 \times 10^{17} »$ ✓

activity $= « λ N = 1.4 \times 10^{10} nuclei per year » = 440 « nuclei per second »$ ✓

Accept conversion to seconds at any stage.

Award [3] marks for a bald correct answer.

Allow ECF from MP1 and MP2

Allow use of decay equation.

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Additional higher level (AHL)

Additional higher level (AHL) » Topic 12: Quantum and nuclear physics » 12.2 – Nuclear physics

Additional higher level (AHL) » Topic 12: Quantum and nuclear physics

Question 21M.2.HL.TZ2.a.ii

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