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Question
Nuclear fission of ${ }^{235} \mathrm{U}$ is one source of electrical energy that has a minimal carbon footprint.
a.i. Natural uranium needs to be enriched to increase the proportion of ${ }^{235} \mathrm{U}$. Suggest a technique that would determine the relative abundances of ${ }^{235} \mathrm{U}$ and ${ }^{238} \mathrm{U}$.
a.ii.Explain how ${ }^{235} \mathrm{U}$ fission results in a chain reaction, including the concept of critical mass.
b. Suggest one reason why there is opposition to the increased use of nuclear fission reactors.
▶️Answer/Explanation
Markscheme
a.i. mass spectrometry/mass spectroscopy/MS
Accept “analysis of radiation emitted”.
[1 mark]
a.ii.critical mass: mass required so that «on average» each fission/reaction results in a further fission/reaction
Any two for [2 max]:
neutron captured by « $^{235} \mathrm{U}$ » nucleus
fission/reaction produces many neutrons/more than one neutron
if these cause further fission/reaction a chain reaction occurs
Accept “minimum mass of fuel needed for the reaction to be self-sustaining”.
Accept answers in the form of suitable diagrams/equations.
[3 marks]
b. produce long lived/long half-life radioisotopes/radioactivity
OR
could be used to produce nuclear weapons
OR
«nuclear» accidents/meltdowns can occur