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On nuclear fusion, Wikipedia reads (about Tritium-Deuterium fusion):

The (intermediate) result of the fusion is an unstable 5He nucleus, which immediately ejects a neutron with 14.1 MeV. The recoil energy of the remaining 4He nucleus is 3.5 MeV, so the total energy liberated is 17.6 MeV. This is many times more than what was needed to overcome the energy [Coulomb] barrier.

I understand that the energy of the 4He nucleus and of the neutron comes from the increase in binding energy of helium in comparison to hydrogen (which let nuclear force the opportunity to work and to release energy). However, I don't understand exactly what force is at play to give the fleeing neutron so much speed. It certainly isn't the electromagnetic force since the neutron is well, neutral.

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The half-life of helium-5 is very short (on the order of $10^{-21}$s). This time scale indicates that this decay is caused by the (residual) strong force. This force depends not only on the distance among nucleons, but also on their spins.

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  • $\begingroup$ Thank you for your answer. Would that then be an instance of the nuclear force being repulsive? $\endgroup$
    – Angus Horner
    Dec 7, 2019 at 16:13
  • $\begingroup$ @AngusHorner : I would think so. $\endgroup$
    – akhmeteli
    Dec 7, 2019 at 16:37

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