Can Protons and Electrons Combine to Form Neutrons?

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Discussion Overview

The discussion revolves around the relationship between protons, electrons, and neutrons, particularly in the context of neutron star formation and the processes involved, such as beta decay and electron capture. Participants explore theoretical aspects and implications of particle interactions in high-energy environments like supernovae.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether protons and electrons can combine to form neutrons, suggesting a simple mass comparison.
  • Another participant asserts that protons and electrons do not combine to form neutrons, citing their quark compositions.
  • A participant discusses the composition of matter in neutron stars, noting the presence of protons, neutrons, electrons, and neutrinos, while questioning the process that leads to neutron star formation.
  • It is proposed that fundamental particles can be converted into each other through interactions, specifically mentioning the conversion of an up quark and an electron into a down quark and a neutrino via W boson exchange.
  • A participant seeks clarification on the duration of beta decay in the context of neutron star formation, linking it to the rapid processes occurring during supernova events.
  • Another participant provides details about the electron capture process, explaining the energy dynamics involved and the conditions under which protons are converted to neutrons during the collapse of a white dwarf.

Areas of Agreement / Disagreement

Participants generally disagree on the possibility of protons and electrons combining to form neutrons, with some asserting it is not possible while others discuss related particle interactions. The discussion remains unresolved regarding the specifics of the processes involved in neutron star formation.

Contextual Notes

Participants express uncertainty about the exact nature of particle interactions and the conditions necessary for processes like beta decay and electron capture, indicating a reliance on specific energy levels and states of matter during neutron star formation.

Stephanus
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Dear PF Forum,
I have a question to ask.
Supernovae produce neutron star (or Black Hole).

This is what I summarize from wikipedia.
Proton
Composition: 2 up quarks, 1 down quark
Mass: 1.672621777(74)E-27 kg

Neutron
Composition: 1 up quark, 2 down quarks
Mass: 1.674927351(74)E-27 kg

Electron
Composition: Electron
Mass: 9.10938291(40)×10E-31 kg

1. Is P + e = N? Is it that simple?
Judging by its mass, altough slightly off.
2. Is Up Quark + e = Down Quark?

Thanks for any answer
 
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Stephanus said:
1. Is P + e = N?

No. As you note, p = uud and n = udd, in terms of quarks.

2. Is Up Quark + e = Down Quark?

No. Up and down quarks are both fundamental particles, not composed of other particles, as far as we know.
 
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jtbell said:
No. As you note, p = uud and n = udd, in terms of quarks.
No. Up and down quarks are both fundamental particles, not composed of other particles, as far as we know.

So, what makes neutron star?
Matter is we know it, consist atom. Proton, Neutron, Electron and I read somewhere, there are abundant neutrinos, too. Altough their combined mass are still much less than combined baryon mass in the universe.
So, if there are Proton, Neutron and Electron, and the result is Neutron star, what makes it?

Thanks.
 
Stephanus said:
So, what makes neutron star?
Mostly neutrons ...

That particles are fundamental does not mean that they cannot be converted into each other. An up quark and an electron may be converted into a down quark and a neutrino by exchanging a W boson. This is what happens in beta decay and when a neutron star is formed (many many many times of course).
 
Orodruin said:
Mostly neutrons ...

That particles are fundamental does not mean that they cannot be converted into each other. An up quark and an electron may be converted into a down quark and a neutrino by exchanging a W boson. This is what happens in beta decay and when a neutron star is formed (many many many times of course).
Thanks Orodruin for your answer, again.
As I know it. The process of producing neutron star is supernova, which happens in 1 seconds. How long is "beta decay"?

Thanks.
 
Stephanus said:
As I know it. The process of producing neutron star is supernova, which happens in 1 seconds. How long is "beta decay"?

The exact name of the interaction would be "electron capture" or one of the inverse beta decays. But still time of interaction won't tell you much. An energy approach can help. In particular the interaction is:
p + e^- \rightarrow n + \nu_e -0.8~MeV
This becomes energetically favorable around at the energies/momenta of the electrons when the white dwarf becomes gravitationally unstable to collapse. And by the end of the collapse, the protons in the core have been converted to neutrons. Neutrons then can't decay back because there is an electron/proton atmosphere in a degenerate state and so the resulting electrons/protons from a neutron beta decay can't find any state to exist in (Pauli-block due to Pauli exclusion principle)
 
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