DP Chemistry (last assessment 2024)

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Question 19M.3.sl.TZ1.12b

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.3.sl.TZ1.12b
Level sl Paper 3 Time zone TZ1
Command term Outline Question number b Adapted from N/A
b.
[Maximum mark: 2]
19M.3.sl.TZ1.12b

Uranium-235, 235U, is bombarded with a neutron causing a fission reaction.

(b)

The critical mass for weapons-grade uranium can be as small as 15 kg. Outline what is meant by critical mass by referring to the equation in (a)(i).

[2]

Markscheme

mass/amount/quantity required so that «on average» each fission/reaction results in a further fission/reaction  [✔]

at least one of the «3» neutrons produced must cause another reaction  [✔]

 

Note: Accept “minimum mass of fuel needed for the reaction to be self-sustaining”.

Examiners report

Less than half the candidates could correctly explain “critical mass” with even fewer combining the definition as the minimum mass for a sustainable fission reaction with the required clarification in terms of neutrons creating a chain reaction.

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