A-LevelPhysicsNuclear physics9702/22 · May/June 2018 · Q76 Marks

A stationary nucleus X decays to form nucleus Y, as shown by the equation X → Y + β⁻ + ν̄.

(a)In the above equation, draw a circle around all symbols that represent a lepton.[1]
(b)State the name of the particle represented by the symbol ν̄.[1]
(c)Energy is released during the decay process. State the form of the energy that is gained by nucleus Y.[1]
(d)By comparing the compositions of X and Y, state and explain whether they are isotopes.[2]
(e)The quark composition of one nucleon in X is changed during the emission of a β⁻ particle. Describe this change to the quark composition.[1]

Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[B1] circle(s) drawn only around β⁻ and ν̄ symbols
[B1] (electron) antineutrino
[B1] kinetic (energy)
[M1] Y has one more proton (and one less neutron)/X has one less proton (and one more neutron) OR Y has more protons (and fewer neutrons)/X has fewer protons (and more neutrons) OR a neutron changes to a proton OR the number of protons increases
[A1] (so) not isotopes
[B1] up down down changes to up up down or udd → uud OR down changes to up or d→u

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