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Conservation of momentum (PLEASE HELP!)

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    Edexcel 2014 June Unit 5 Q18(a)(iii)

    In the fusion of one deuterium nucleus with one tritium nucleus, one helium and one neutron are produced.

    The question is "Explain why most of the energy released in this fusion is transferred to kinetic energy of the neutron"

    Mark scheme:
    -Momentum is conserved
    -Mass of neutron is smaller so speed is greater
    -By KE=1/2mv^2, so neutron's KE is greater

    But I was thinking the momentum of helium and neutron can be different after fusion, right??
    That is the speed of the neutron can be smaller than that of helium.

    They just need to have a total sum of momentum that equals initial momentum.

    So why does KE of neutron greater than that of helium?
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