Deuterium as opposed to di-proton

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    Deuterium
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Discussion Overview

The discussion revolves around the formation of deuterium from hydrogen nuclei during nucleosynthesis, specifically addressing why two protons do not simply form a di-proton instead. Participants explore the role of the strong nuclear force and the conditions under which deuterium is formed, as well as the conversion of protons to neutrons.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions why two protons do not form a di-proton instead of deuterium, suggesting that the strength of the strong nuclear force plays a role.
  • Another participant explains that the nuclear force between a neutron and a proton is stronger than the force between two protons or two neutrons, making deuterium formation more favorable.
  • It is noted that the process of forming deuterium from two protons is rare and typically involves a higher energy interaction, such as p+p--> d+pion+.
  • A participant inquires about the mechanism by which a proton becomes a neutron, suggesting it may involve quark conversion and energy considerations.
  • Discussion includes the historical context of nucleosynthesis, where neutrons were produced alongside protons in the early universe, facilitating deuterium formation.
  • Another participant raises the question of the stability of free neutrons and their tendency to decay if not bound within a nucleus.
  • A later reply provides information about the neutron's lifetime, indicating that it is relatively stable on the timescale of early nucleosynthesis.

Areas of Agreement / Disagreement

Participants express various viewpoints regarding the mechanisms of nucleosynthesis and the stability of nuclear formations, with no consensus reached on the specific processes involved in proton-to-neutron conversion or the implications of neutron stability.

Contextual Notes

The discussion touches on complex interactions within nuclear physics, including the nuances of the strong nuclear force and the conditions required for different nuclear reactions, without resolving the underlying assumptions or dependencies on specific definitions.

Jorge Kluney
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Hello,

I was having a difficult time understanding some instances of nucleosynthesis. Two hydrogens (each with just 1 proton) come together to form deuterium (1 proton and 1 neutron)... but why does this happen as opposed to forming a di-proton (2 protons). I've been told that it has something to do with the strength of strong nuclear force. That if the force were stronger than it would be a di-proton as opposed to deuterium... but then the rate of stars burning would be too rapid.

Does one of the protons convert to a neutron while forming deuterium as opposed to a di-proton?
Thanks for any help.
 
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Jorge Kluney said:
Hello,
I was having a difficult time understanding some instances of nucleosynthesis. Two hydrogens (each with just 1 proton) come together to form deuterium (1 proton and 1 neutron)... but why does this happen as opposed to forming a di-proton (2 protons). I've been told that it has something to do with the strength of strong nuclear force. That if the force were stronger than it would be a di-proton as opposed to deuterium... but then the rate of stars burning would be too rapid.
Does one of the protons convert to a neutron while forming deuterium as opposed to a di-proton?
Thanks for any help.

The reason there is no stable di-proton has to do with the details of the nuclear force. The force between a neutron and a proton is slightly stronger than either the p-p force or the n-n force. (The technical reason has to do with "isotopic spin".) The n-p force is just barely strong enough to bind them into the deuteron, but the n-n and p-p forces are not strong enough to bind. The answer to your last question is that it is very rare for two protons to form a deuteron. The process would have to be something like p+p--> d+pion^+, which doesn't usually happen.
The deuterons in stars come from low energy, n and p coming together and binding, usually with the emission of a photon. The process is called
"radiate capture". It is similar to how electrons get captured by protons to form the hydrogen atom.
 
Thanks for that reply. It was very helpful.

In regards to the deuterium being composed of n-p. How does one of those protons (hydrogen) become a neutron? Does it need to gain energy (sorry if this is the wrong descriptive term)? Does one of the existing protons have one of its 'u quarks' convert to a 'd quark'?
Thanks again.
 
If you are going back to the early universe, neutrons were produced as easily as protons, so both were around to create a deuteron by the process n+p--> d+ photon. If you start with p-p, forming a deuteron is vey unlikely since p+p--> d+pion can only happen at relatively high energy where forming a deuteron is unlikely.
 
Thanks again!
So, there was already free amounts of neutrons to be used in forming deuteron. Were those neutrons (neutrons free being joined with a proton in deuteron) unstable? Did they quickly breakdown to a proton-electron-antineutrino if they weren't held in a nucleus with a proton?
 
The neutron lifetime is about 15 minutes, which is almost infinite on the time scale of early nucleosynthesis.
 

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