A stationary nucleus P of mass 243u decays by emitting an α-particle of mass 4u to form a different nucleus Q, as illustrated in [Figure 7.1]. The initial speed of the α-particle is 1.6 × 10⁷ m s⁻¹.

1. (a)Use the principle of conservation of momentum to explain why the initial velocities of nucleus Q and the α-particle must be in opposite directions.[2]
2. (b)Determine the initial speed v of nucleus Q. v = ............................................................ m s⁻¹[2]
3. (c)Calculate the initial kinetic energy, in MeV, of the α-particle. kinetic energy = ............................................................ MeV[3]
4. (d)(i)A graph of number of neutrons N against proton number Z is shown in [Figure 7.2]. The graph shows a cross that represents nucleus P. A nucleus R has a nucleon number of 242 and is an isotope of nucleus P. Nucleus R decays by emitting a β⁻ particle to form a different nucleus S. (i) On [Figure 7.2], draw a cross to represent: 1. nucleus R (label this cross R) 2. nucleus S (label this cross S).[2]
5. (d)(ii)(ii) State the name of the other lepton, in addition to the β⁻ particle, that is emitted during the decay of nucleus R.[1]

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