A-LevelPhysicsNuclear physics9702/41 · Oct/Nov 2018 · Q119 Marks

A stationary isolated nucleus emits a γ-ray photon of energy 0.51 MeV.

(a)State what is meant by a photon.[2]
(b)(i)For the γ-ray photon, calculate its wavelength, wavelength = ........................................................... m[2]
(b)(ii)For the γ-ray photon, calculate its momentum. momentum = ........................................................... Ns[2]
(c)(i)For this nucleus, determine the change in mass Δm during the decay that gives rise to the energy of the γ-ray photon. Δm = ........................................................... kg[2]
(c)(ii)Explain why, after the decay, the nucleus is no longer stationary.[1]

Mark scheme

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

[M1] discrete amount/quantum/packet of energy
[A1] of electromagnetic radiation
[C1] energy = hc/λ
[A1] λ = (6.63 × 10⁻³⁴ × 3.00 × 10⁸)/(0.51 × 10⁶ × 1.60 × 10⁻¹⁹) = 2.4 x 10⁻¹² m
[C1] p = h/λ or p = E/c
[A1] = (6.63 × 10⁻³⁴)/(2.44 × 10⁻¹²) or = (0.51 × 1.60 × 10⁻¹³)/(3.00 × 10⁸) = 2.7 × 10⁻²² N s
[C1] E = c²Δm
[A1] Δm = (0.51 × 1.60 × 10⁻¹³)/(3.00 × 10⁸)² = 9.1 x 10⁻³¹ kg
[B1] (momentum is conserved so) nucleus must have momentum in opposite direction to photon

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