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Light Water Nuclear Reactors (LWNR) need enriched uranium fuel rods since the light water coolant tends to absorb in addition to moderating neutrons. What happens when a regular hydrogen atom, just proton in nucleus ie Protium, absorbs a free neutron?

My guess is that it becomes a deuterium atom, but I know it depends on the incident energy of neutron. I am assuming that a deuterium nucleus is more stable that a lone proton nucleus, so this would likely be exothermic with energy being released as either gamma ray, kinetic energy of molecule, or both.

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Yes for slow neutrons, many combine with a hydrogen proton to form deuterium. Deuterium is more stable than a hydrogen with a single proton and is quite stable. Faster neutrons will elastically scatter off the hydrogen nucleus conserving, of course, both energy and momentum. When the proton captures the neutron forming deuterium a gamma ray of energy 2.2 MeV is emitted.

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    $\begingroup$ Deuterium is more stable than an isolated proton plus an isolated neutron. $\endgroup$
    – Jon Custer
    Commented Sep 28, 2017 at 17:01
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    $\begingroup$ @Jon Custer, I guess I have forgotten some basic nuclear physics because i'm confused how deuterium is more stable than a single proton or a neutron which decays. i $\endgroup$
    – Natsfan
    Commented Sep 28, 2017 at 17:12
  • $\begingroup$ @jmh Empirically yo note that you get about 2.2 MeV in gammas from $p + n \to d$... $\endgroup$
    – dmckee --- ex-moderator kitten
    Commented Sep 28, 2017 at 17:19
  • $\begingroup$ Deuterium is a stable nucleus, meaning it is energetically favored over breaking into isolated particles. Why? The strong force binds nucleons together. There is no Coulomb repulsion. Now tritium is unstable, but to beta decay to 3He, not breaking apart. $\endgroup$
    – Jon Custer
    Commented Sep 28, 2017 at 17:20
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    $\begingroup$ Yes I understand that but both apply to a single proton as well. Sorry to sound so dense. $\endgroup$
    – Natsfan
    Commented Sep 28, 2017 at 17:46

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