A-LevelPhysicsNuclear physics9702/42 · Oct/Nov 2020 · Q127 Marks

A student suggests that one possible nuclear reaction is ⁵⁶₂₆Fe + ¹₀n → ²⁰₉F + ³⁷₁₇Cl. The binding energy per nucleon of a nucleus varies with the nucleon number. Use this variation to explain why the reaction would not result in an overall release of energy.

(a)(i)Define nuclear binding energy.[2]
(a)(ii)Explain what is meant by a nuclear fission reaction.[2]
(b)A student suggests that one possible nuclear reaction is ⁵⁶₂₆Fe + ¹₀n → ²⁰₉F + ³⁷₁₇Cl. The binding energy per nucleon of a nucleus varies with the nucleon number. Use this variation to explain why the reaction would not result in an overall release of energy.[3]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.

[M1] energy required to separate nucleons (of nucleus)
[A1] to infinity
[B1] a (single) large nucleus divides to form (smaller) nuclei
[B1] any one point from: • initiated by neutron bombardment • resulting nuclei are of similar size • binding energy per nucleon increases • total binding energy increases • neutrons released • combined mass of smaller nuclei is less than mass of large nucleus
[B1] binding energy per nucleon is a maximum at around A = 56
[B1] products of splitting a ⁵⁶Fe nucleus must have a lower total binding energy
[B1] (reaction would require) a net input of energy

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