A-LevelPhysicsNuclear physics9702/22 · Oct/Nov 2017 · Q76 Marks
A stationary nucleus X decays by emitting a ẞ⁺ particle to form a nucleus of carbon-13 (¹³C). An incomplete equation to represent this decay is X → ¹³C + ẞ⁺.
- (a)State the name of the class (group) of particles that includes ẞ⁺.[1]
- (b)For nucleus X, state the number of protons, neutrons.[1]
- (c)The carbon-13 nucleus has a mass of 2.2 × 10⁻²⁶ kg. Its kinetic energy as a result of the decay process is 0.80 MeV. Calculate the speed of this nucleus.[3]
- (d)Explain why the sum of the kinetic energies of the carbon-13 nucleus and the ẞ⁺ particle cannot be equal to the total energy released by the decay process.[1]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.
- [B1] lepton(s)
- [A1] protons: 7 and neutrons: 6
- [C1] E = ½mv²
- [C1] Kinetic energy = 0.80 × 10⁶ × 1.60 × 10⁻¹⁹ = 1.28 × 10⁻¹³ (J)
- [A1] v = √(2E/m) = √(2 × 1.28 × 10⁻¹³ / 2.2 × 10⁻²⁶) = 3.4 × 10⁶ m s⁻¹
- [B1] an (electron) neutrino/v(e) is also produced (and this has energy)
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