A-LevelPhysicsParticle physics9702/21 · Oct/Nov 2017 · Q85 Marks
A neutron within a nucleus decays to produce a proton, a β⁻ particle and an (electron) antineutrino. n → p + β⁻ + ν̄
- (a)Use the quark composition of the neutron to show that the neutron has no charge.[3]
- (b)Complete Fig. 8.1 by giving appropriate values of the charge and the mass of the proton, the β⁻ particle and the (electron) antineutrino. [Figure 8.1][2]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.
- [B1] (quark structure is) up, down, down/udd
- [C1] up/u has charge +⅔(e), down/d has charge -⅓(e)
- [A1] +⅔e -⅓e -⅓e = 0
- [B1] charge: p +1.6(0) × 10⁻¹⁹ (C) or +e β⁻ -1.6(0) × 10⁻¹⁹ (C) or –e ν̄ zero/0
- [B1] mass: p 1.67 × 10⁻²⁷ (kg)/1.7 × 10⁻²⁷ (kg) β⁻ 9.1(1) × 10⁻³¹ (kg) ν̄ very small/zero/0
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