DP Chemistry (last assessment 2024)
Question 19M.3.sl.TZ1.b
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.sl.TZ1.b |
| 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.b
Uranium-235, 235U, is bombarded with a neutron causing a fission reaction.
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.
