Why does this quiz question say that protons and electrons do not combine to form neutrons?












8












$begingroup$


I read this somewhere:




Where are the protons and electrons in a neutron star? When the neutron star forms, most of the protons and electrons combine together to form neutrons.




But on a true/false quiz, I saw the question




A neutron is formed by an electron and a proton combining together and therefore it is neutral.




but the answer was false. Why are these not contradictory?






electrons nuclear-physics neutrons protons







share|cite|improve this question











$endgroup$








  • 8




    $begingroup$
    False. Such a combination of a proton and electron is indeed possible, but the process also involves an electron neutrino apart from the neutron. You cannot create a fermion such as neutron by simply putting together two other fermions such as proton and electron. Seach for the keyword "electron capture" for more information.
    $endgroup$
    – Tomáš Brauner
    9 hours ago






  • 2




    $begingroup$
    @TomášBrauner That seems like an answer to the question, rather than a comment.
    $endgroup$
    – rob♦
    9 hours ago






  • 1




    $begingroup$
    It is unclear what question you are asking. Is the title your question? Or do you want to know the proper reaction equation for the formation of neutrons in a neutron star? Or something else.
    $endgroup$
    – Bill N
    9 hours ago


















8












$begingroup$


I read this somewhere:




Where are the protons and electrons in a neutron star? When the neutron star forms, most of the protons and electrons combine together to form neutrons.




But on a true/false quiz, I saw the question




A neutron is formed by an electron and a proton combining together and therefore it is neutral.




but the answer was false. Why are these not contradictory?






electrons nuclear-physics neutrons protons







share|cite|improve this question











$endgroup$








  • 8




    $begingroup$
    False. Such a combination of a proton and electron is indeed possible, but the process also involves an electron neutrino apart from the neutron. You cannot create a fermion such as neutron by simply putting together two other fermions such as proton and electron. Seach for the keyword "electron capture" for more information.
    $endgroup$
    – Tomáš Brauner
    9 hours ago






  • 2




    $begingroup$
    @TomášBrauner That seems like an answer to the question, rather than a comment.
    $endgroup$
    – rob♦
    9 hours ago






  • 1




    $begingroup$
    It is unclear what question you are asking. Is the title your question? Or do you want to know the proper reaction equation for the formation of neutrons in a neutron star? Or something else.
    $endgroup$
    – Bill N
    9 hours ago
















8












8








8


1



$begingroup$


I read this somewhere:




Where are the protons and electrons in a neutron star? When the neutron star forms, most of the protons and electrons combine together to form neutrons.




But on a true/false quiz, I saw the question




A neutron is formed by an electron and a proton combining together and therefore it is neutral.




but the answer was false. Why are these not contradictory?






electrons nuclear-physics neutrons protons







share|cite|improve this question











$endgroup$




I read this somewhere:




Where are the protons and electrons in a neutron star? When the neutron star forms, most of the protons and electrons combine together to form neutrons.




But on a true/false quiz, I saw the question




A neutron is formed by an electron and a proton combining together and therefore it is neutral.




but the answer was false. Why are these not contradictory?






electrons nuclear-physics neutrons protons




electrons nuclear-physics neutrons protons






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited 5 hours ago









knzhou

44.3k11121213




44.3k11121213










asked 10 hours ago









Arifa AkhtarArifa Akhtar

562




562








  • 8




    $begingroup$
    False. Such a combination of a proton and electron is indeed possible, but the process also involves an electron neutrino apart from the neutron. You cannot create a fermion such as neutron by simply putting together two other fermions such as proton and electron. Seach for the keyword "electron capture" for more information.
    $endgroup$
    – Tomáš Brauner
    9 hours ago






  • 2




    $begingroup$
    @TomášBrauner That seems like an answer to the question, rather than a comment.
    $endgroup$
    – rob♦
    9 hours ago






  • 1




    $begingroup$
    It is unclear what question you are asking. Is the title your question? Or do you want to know the proper reaction equation for the formation of neutrons in a neutron star? Or something else.
    $endgroup$
    – Bill N
    9 hours ago
















  • 8




    $begingroup$
    False. Such a combination of a proton and electron is indeed possible, but the process also involves an electron neutrino apart from the neutron. You cannot create a fermion such as neutron by simply putting together two other fermions such as proton and electron. Seach for the keyword "electron capture" for more information.
    $endgroup$
    – Tomáš Brauner
    9 hours ago






  • 2




    $begingroup$
    @TomášBrauner That seems like an answer to the question, rather than a comment.
    $endgroup$
    – rob♦
    9 hours ago






  • 1




    $begingroup$
    It is unclear what question you are asking. Is the title your question? Or do you want to know the proper reaction equation for the formation of neutrons in a neutron star? Or something else.
    $endgroup$
    – Bill N
    9 hours ago










8




8




$begingroup$
False. Such a combination of a proton and electron is indeed possible, but the process also involves an electron neutrino apart from the neutron. You cannot create a fermion such as neutron by simply putting together two other fermions such as proton and electron. Seach for the keyword "electron capture" for more information.
$endgroup$
– Tomáš Brauner
9 hours ago




$begingroup$
False. Such a combination of a proton and electron is indeed possible, but the process also involves an electron neutrino apart from the neutron. You cannot create a fermion such as neutron by simply putting together two other fermions such as proton and electron. Seach for the keyword "electron capture" for more information.
$endgroup$
– Tomáš Brauner
9 hours ago




2




2




$begingroup$
@TomášBrauner That seems like an answer to the question, rather than a comment.
$endgroup$
– rob♦
9 hours ago




$begingroup$
@TomášBrauner That seems like an answer to the question, rather than a comment.
$endgroup$
– rob♦
9 hours ago




1




1




$begingroup$
It is unclear what question you are asking. Is the title your question? Or do you want to know the proper reaction equation for the formation of neutrons in a neutron star? Or something else.
$endgroup$
– Bill N
9 hours ago






$begingroup$
It is unclear what question you are asking. Is the title your question? Or do you want to know the proper reaction equation for the formation of neutrons in a neutron star? Or something else.
$endgroup$
– Bill N
9 hours ago












2 Answers
2






active

oldest

votes


















17












$begingroup$

You're asking about two distinct phenomena. The difference between them is subtle, and I think there is some context missing from the second question that you quote, which makes things more confusing than they need to be.




When the neutron star forms, most of the protons and electrons combine together to form neutrons




This is mostly correct. The process is known as "electron capture," and the full reaction is



$$rm p + e^- to n + nu_e$$



The other particle in the final state (represented by a nu) is a neutrino. The neutrino is an uncharged, very low-mass electron-like particle, in the same way that neutrons and protons are different charge states of the same sort of particle. So far as we know, in physics, the number of electron-like "leptons" and the number of proton-like "baryons" isn't changed in any physical process. The neutrinos play an important role in the dynamics of the stellar collapses where neutron stars are formed, but in some authors who write very elementary explanations of neutron stars will leave the neutrinos out of their descriptions. There are advantages and disadvantages to this approach; your confusion here is one of the disadvantages.




A neutron is formed by an electron and a proton combining together, therefore it is neutral: true or false? Answer: false




This is a fundamentally flawed true-false question, because it makes several statements at the same time, some of which are correct. The question I was expecting to find here, based on the title of your question, was more like




The neutron is an electron and a proton that are "stuck together" somehow. (Answer: false)




We have another name for an electron and a proton that are semi-permanently "stuck together," and the dynamics of that system are very different from the dynamics of the neutron.



When you "combine together" macroscopic objects in ordinary life, the things that you combined are still somehow present in the combination. But in particle physics, the situation is different. The electron-capture process that we're talking about here fundamentally changes both the baryon and the lepton parts of the system. To the extent that a neutron behaves like a composite particle, it behaves as if it is made out of quarks.






share|cite|improve this answer









$endgroup$













  • $begingroup$
    So where do the neutrinos come from, to facilitate the electron capture? I was under the impression that they're virtually massless particles that can travel through entire planets without interacting with anything; how do you get an entire star's worth of protons capturing them as they're decaying into a neutron star?
    $endgroup$
    – Mason Wheeler
    6 hours ago






  • 5




    $begingroup$
    @MasonWheeler: The neutrino is listed as a product, not a reactant.
    $endgroup$
    – user2357112
    6 hours ago










  • $begingroup$
    ...oh. OK, that makes more sense.
    $endgroup$
    – Mason Wheeler
    6 hours ago






  • 1




    $begingroup$
    @MasonWheeler although there is a process commonly called "inverse beta decay" where a proton "captures" an antineutrino and transmutes into a neutron while emitting a positron (anti-electron). There are neutrinos whizzing about everywhere, so they are always available for such reactions.
    $endgroup$
    – thegreatemu
    5 hours ago






  • 2




    $begingroup$
    @thegreatemu Partly true. Most of the background neutrinos don't have enough energy to drive inverse beta decay. This is a subject of vigorous discussion in the neutrino detection community.
    $endgroup$
    – rob♦
    5 hours ago



















7












$begingroup$

It's not exactly a myth that protons and electrons combine to form neutrons, but it's not very accurate. A proton and electron can react to produce a neutron, but a neutron isn't simply a composite particle consisting of a proton joined to an electron.



Protons and neutrons are hadrons, which means they consist of 3 quarks. A proton has 2 up quarks & 1 down quark, a neutron has 1 up quark and 2 down quarks. These quarks are bound together by gluons (and a bunch of virtual quarks, but don't worry about them for now).



When a proton & electron react an up quark in the proton is converted to a down quark, and the electron is converted to a neutrino. This process is mediated by a $W^+$ boson. I can't find a good diagram of this exact process, but here's a diagram from Wikipedia of a closely related process: the decay of a neutron into a proton, electron, and antineutrino.



neutron decay



The diagram for the proton + electron reaction is very similar, just reverse the time direction, and swap the $W^-$ to a $W^+$, and the antineutrino to a neutrino.






share|cite|improve this answer









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    2 Answers
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    2 Answers
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    17












    $begingroup$

    You're asking about two distinct phenomena. The difference between them is subtle, and I think there is some context missing from the second question that you quote, which makes things more confusing than they need to be.




    When the neutron star forms, most of the protons and electrons combine together to form neutrons




    This is mostly correct. The process is known as "electron capture," and the full reaction is



    $$rm p + e^- to n + nu_e$$



    The other particle in the final state (represented by a nu) is a neutrino. The neutrino is an uncharged, very low-mass electron-like particle, in the same way that neutrons and protons are different charge states of the same sort of particle. So far as we know, in physics, the number of electron-like "leptons" and the number of proton-like "baryons" isn't changed in any physical process. The neutrinos play an important role in the dynamics of the stellar collapses where neutron stars are formed, but in some authors who write very elementary explanations of neutron stars will leave the neutrinos out of their descriptions. There are advantages and disadvantages to this approach; your confusion here is one of the disadvantages.




    A neutron is formed by an electron and a proton combining together, therefore it is neutral: true or false? Answer: false




    This is a fundamentally flawed true-false question, because it makes several statements at the same time, some of which are correct. The question I was expecting to find here, based on the title of your question, was more like




    The neutron is an electron and a proton that are "stuck together" somehow. (Answer: false)




    We have another name for an electron and a proton that are semi-permanently "stuck together," and the dynamics of that system are very different from the dynamics of the neutron.



    When you "combine together" macroscopic objects in ordinary life, the things that you combined are still somehow present in the combination. But in particle physics, the situation is different. The electron-capture process that we're talking about here fundamentally changes both the baryon and the lepton parts of the system. To the extent that a neutron behaves like a composite particle, it behaves as if it is made out of quarks.






    share|cite|improve this answer









    $endgroup$













    • $begingroup$
      So where do the neutrinos come from, to facilitate the electron capture? I was under the impression that they're virtually massless particles that can travel through entire planets without interacting with anything; how do you get an entire star's worth of protons capturing them as they're decaying into a neutron star?
      $endgroup$
      – Mason Wheeler
      6 hours ago






    • 5




      $begingroup$
      @MasonWheeler: The neutrino is listed as a product, not a reactant.
      $endgroup$
      – user2357112
      6 hours ago










    • $begingroup$
      ...oh. OK, that makes more sense.
      $endgroup$
      – Mason Wheeler
      6 hours ago






    • 1




      $begingroup$
      @MasonWheeler although there is a process commonly called "inverse beta decay" where a proton "captures" an antineutrino and transmutes into a neutron while emitting a positron (anti-electron). There are neutrinos whizzing about everywhere, so they are always available for such reactions.
      $endgroup$
      – thegreatemu
      5 hours ago






    • 2




      $begingroup$
      @thegreatemu Partly true. Most of the background neutrinos don't have enough energy to drive inverse beta decay. This is a subject of vigorous discussion in the neutrino detection community.
      $endgroup$
      – rob♦
      5 hours ago
















    17












    $begingroup$

    You're asking about two distinct phenomena. The difference between them is subtle, and I think there is some context missing from the second question that you quote, which makes things more confusing than they need to be.




    When the neutron star forms, most of the protons and electrons combine together to form neutrons




    This is mostly correct. The process is known as "electron capture," and the full reaction is



    $$rm p + e^- to n + nu_e$$



    The other particle in the final state (represented by a nu) is a neutrino. The neutrino is an uncharged, very low-mass electron-like particle, in the same way that neutrons and protons are different charge states of the same sort of particle. So far as we know, in physics, the number of electron-like "leptons" and the number of proton-like "baryons" isn't changed in any physical process. The neutrinos play an important role in the dynamics of the stellar collapses where neutron stars are formed, but in some authors who write very elementary explanations of neutron stars will leave the neutrinos out of their descriptions. There are advantages and disadvantages to this approach; your confusion here is one of the disadvantages.




    A neutron is formed by an electron and a proton combining together, therefore it is neutral: true or false? Answer: false




    This is a fundamentally flawed true-false question, because it makes several statements at the same time, some of which are correct. The question I was expecting to find here, based on the title of your question, was more like




    The neutron is an electron and a proton that are "stuck together" somehow. (Answer: false)




    We have another name for an electron and a proton that are semi-permanently "stuck together," and the dynamics of that system are very different from the dynamics of the neutron.



    When you "combine together" macroscopic objects in ordinary life, the things that you combined are still somehow present in the combination. But in particle physics, the situation is different. The electron-capture process that we're talking about here fundamentally changes both the baryon and the lepton parts of the system. To the extent that a neutron behaves like a composite particle, it behaves as if it is made out of quarks.






    share|cite|improve this answer









    $endgroup$













    • $begingroup$
      So where do the neutrinos come from, to facilitate the electron capture? I was under the impression that they're virtually massless particles that can travel through entire planets without interacting with anything; how do you get an entire star's worth of protons capturing them as they're decaying into a neutron star?
      $endgroup$
      – Mason Wheeler
      6 hours ago






    • 5




      $begingroup$
      @MasonWheeler: The neutrino is listed as a product, not a reactant.
      $endgroup$
      – user2357112
      6 hours ago










    • $begingroup$
      ...oh. OK, that makes more sense.
      $endgroup$
      – Mason Wheeler
      6 hours ago






    • 1




      $begingroup$
      @MasonWheeler although there is a process commonly called "inverse beta decay" where a proton "captures" an antineutrino and transmutes into a neutron while emitting a positron (anti-electron). There are neutrinos whizzing about everywhere, so they are always available for such reactions.
      $endgroup$
      – thegreatemu
      5 hours ago






    • 2




      $begingroup$
      @thegreatemu Partly true. Most of the background neutrinos don't have enough energy to drive inverse beta decay. This is a subject of vigorous discussion in the neutrino detection community.
      $endgroup$
      – rob♦
      5 hours ago














    17












    17








    17





    $begingroup$

    You're asking about two distinct phenomena. The difference between them is subtle, and I think there is some context missing from the second question that you quote, which makes things more confusing than they need to be.




    When the neutron star forms, most of the protons and electrons combine together to form neutrons




    This is mostly correct. The process is known as "electron capture," and the full reaction is



    $$rm p + e^- to n + nu_e$$



    The other particle in the final state (represented by a nu) is a neutrino. The neutrino is an uncharged, very low-mass electron-like particle, in the same way that neutrons and protons are different charge states of the same sort of particle. So far as we know, in physics, the number of electron-like "leptons" and the number of proton-like "baryons" isn't changed in any physical process. The neutrinos play an important role in the dynamics of the stellar collapses where neutron stars are formed, but in some authors who write very elementary explanations of neutron stars will leave the neutrinos out of their descriptions. There are advantages and disadvantages to this approach; your confusion here is one of the disadvantages.




    A neutron is formed by an electron and a proton combining together, therefore it is neutral: true or false? Answer: false




    This is a fundamentally flawed true-false question, because it makes several statements at the same time, some of which are correct. The question I was expecting to find here, based on the title of your question, was more like




    The neutron is an electron and a proton that are "stuck together" somehow. (Answer: false)




    We have another name for an electron and a proton that are semi-permanently "stuck together," and the dynamics of that system are very different from the dynamics of the neutron.



    When you "combine together" macroscopic objects in ordinary life, the things that you combined are still somehow present in the combination. But in particle physics, the situation is different. The electron-capture process that we're talking about here fundamentally changes both the baryon and the lepton parts of the system. To the extent that a neutron behaves like a composite particle, it behaves as if it is made out of quarks.






    share|cite|improve this answer









    $endgroup$



    You're asking about two distinct phenomena. The difference between them is subtle, and I think there is some context missing from the second question that you quote, which makes things more confusing than they need to be.




    When the neutron star forms, most of the protons and electrons combine together to form neutrons




    This is mostly correct. The process is known as "electron capture," and the full reaction is



    $$rm p + e^- to n + nu_e$$



    The other particle in the final state (represented by a nu) is a neutrino. The neutrino is an uncharged, very low-mass electron-like particle, in the same way that neutrons and protons are different charge states of the same sort of particle. So far as we know, in physics, the number of electron-like "leptons" and the number of proton-like "baryons" isn't changed in any physical process. The neutrinos play an important role in the dynamics of the stellar collapses where neutron stars are formed, but in some authors who write very elementary explanations of neutron stars will leave the neutrinos out of their descriptions. There are advantages and disadvantages to this approach; your confusion here is one of the disadvantages.




    A neutron is formed by an electron and a proton combining together, therefore it is neutral: true or false? Answer: false




    This is a fundamentally flawed true-false question, because it makes several statements at the same time, some of which are correct. The question I was expecting to find here, based on the title of your question, was more like




    The neutron is an electron and a proton that are "stuck together" somehow. (Answer: false)




    We have another name for an electron and a proton that are semi-permanently "stuck together," and the dynamics of that system are very different from the dynamics of the neutron.



    When you "combine together" macroscopic objects in ordinary life, the things that you combined are still somehow present in the combination. But in particle physics, the situation is different. The electron-capture process that we're talking about here fundamentally changes both the baryon and the lepton parts of the system. To the extent that a neutron behaves like a composite particle, it behaves as if it is made out of quarks.







    share|cite|improve this answer












    share|cite|improve this answer



    share|cite|improve this answer










    answered 9 hours ago









    rob♦rob

    40.9k972168




    40.9k972168












    • $begingroup$
      So where do the neutrinos come from, to facilitate the electron capture? I was under the impression that they're virtually massless particles that can travel through entire planets without interacting with anything; how do you get an entire star's worth of protons capturing them as they're decaying into a neutron star?
      $endgroup$
      – Mason Wheeler
      6 hours ago






    • 5




      $begingroup$
      @MasonWheeler: The neutrino is listed as a product, not a reactant.
      $endgroup$
      – user2357112
      6 hours ago










    • $begingroup$
      ...oh. OK, that makes more sense.
      $endgroup$
      – Mason Wheeler
      6 hours ago






    • 1




      $begingroup$
      @MasonWheeler although there is a process commonly called "inverse beta decay" where a proton "captures" an antineutrino and transmutes into a neutron while emitting a positron (anti-electron). There are neutrinos whizzing about everywhere, so they are always available for such reactions.
      $endgroup$
      – thegreatemu
      5 hours ago






    • 2




      $begingroup$
      @thegreatemu Partly true. Most of the background neutrinos don't have enough energy to drive inverse beta decay. This is a subject of vigorous discussion in the neutrino detection community.
      $endgroup$
      – rob♦
      5 hours ago


















    • $begingroup$
      So where do the neutrinos come from, to facilitate the electron capture? I was under the impression that they're virtually massless particles that can travel through entire planets without interacting with anything; how do you get an entire star's worth of protons capturing them as they're decaying into a neutron star?
      $endgroup$
      – Mason Wheeler
      6 hours ago






    • 5




      $begingroup$
      @MasonWheeler: The neutrino is listed as a product, not a reactant.
      $endgroup$
      – user2357112
      6 hours ago










    • $begingroup$
      ...oh. OK, that makes more sense.
      $endgroup$
      – Mason Wheeler
      6 hours ago






    • 1




      $begingroup$
      @MasonWheeler although there is a process commonly called "inverse beta decay" where a proton "captures" an antineutrino and transmutes into a neutron while emitting a positron (anti-electron). There are neutrinos whizzing about everywhere, so they are always available for such reactions.
      $endgroup$
      – thegreatemu
      5 hours ago






    • 2




      $begingroup$
      @thegreatemu Partly true. Most of the background neutrinos don't have enough energy to drive inverse beta decay. This is a subject of vigorous discussion in the neutrino detection community.
      $endgroup$
      – rob♦
      5 hours ago
















    $begingroup$
    So where do the neutrinos come from, to facilitate the electron capture? I was under the impression that they're virtually massless particles that can travel through entire planets without interacting with anything; how do you get an entire star's worth of protons capturing them as they're decaying into a neutron star?
    $endgroup$
    – Mason Wheeler
    6 hours ago




    $begingroup$
    So where do the neutrinos come from, to facilitate the electron capture? I was under the impression that they're virtually massless particles that can travel through entire planets without interacting with anything; how do you get an entire star's worth of protons capturing them as they're decaying into a neutron star?
    $endgroup$
    – Mason Wheeler
    6 hours ago




    5




    5




    $begingroup$
    @MasonWheeler: The neutrino is listed as a product, not a reactant.
    $endgroup$
    – user2357112
    6 hours ago




    $begingroup$
    @MasonWheeler: The neutrino is listed as a product, not a reactant.
    $endgroup$
    – user2357112
    6 hours ago












    $begingroup$
    ...oh. OK, that makes more sense.
    $endgroup$
    – Mason Wheeler
    6 hours ago




    $begingroup$
    ...oh. OK, that makes more sense.
    $endgroup$
    – Mason Wheeler
    6 hours ago




    1




    1




    $begingroup$
    @MasonWheeler although there is a process commonly called "inverse beta decay" where a proton "captures" an antineutrino and transmutes into a neutron while emitting a positron (anti-electron). There are neutrinos whizzing about everywhere, so they are always available for such reactions.
    $endgroup$
    – thegreatemu
    5 hours ago




    $begingroup$
    @MasonWheeler although there is a process commonly called "inverse beta decay" where a proton "captures" an antineutrino and transmutes into a neutron while emitting a positron (anti-electron). There are neutrinos whizzing about everywhere, so they are always available for such reactions.
    $endgroup$
    – thegreatemu
    5 hours ago




    2




    2




    $begingroup$
    @thegreatemu Partly true. Most of the background neutrinos don't have enough energy to drive inverse beta decay. This is a subject of vigorous discussion in the neutrino detection community.
    $endgroup$
    – rob♦
    5 hours ago




    $begingroup$
    @thegreatemu Partly true. Most of the background neutrinos don't have enough energy to drive inverse beta decay. This is a subject of vigorous discussion in the neutrino detection community.
    $endgroup$
    – rob♦
    5 hours ago











    7












    $begingroup$

    It's not exactly a myth that protons and electrons combine to form neutrons, but it's not very accurate. A proton and electron can react to produce a neutron, but a neutron isn't simply a composite particle consisting of a proton joined to an electron.



    Protons and neutrons are hadrons, which means they consist of 3 quarks. A proton has 2 up quarks & 1 down quark, a neutron has 1 up quark and 2 down quarks. These quarks are bound together by gluons (and a bunch of virtual quarks, but don't worry about them for now).



    When a proton & electron react an up quark in the proton is converted to a down quark, and the electron is converted to a neutrino. This process is mediated by a $W^+$ boson. I can't find a good diagram of this exact process, but here's a diagram from Wikipedia of a closely related process: the decay of a neutron into a proton, electron, and antineutrino.



    neutron decay



    The diagram for the proton + electron reaction is very similar, just reverse the time direction, and swap the $W^-$ to a $W^+$, and the antineutrino to a neutrino.






    share|cite|improve this answer









    $endgroup$


















      7












      $begingroup$

      It's not exactly a myth that protons and electrons combine to form neutrons, but it's not very accurate. A proton and electron can react to produce a neutron, but a neutron isn't simply a composite particle consisting of a proton joined to an electron.



      Protons and neutrons are hadrons, which means they consist of 3 quarks. A proton has 2 up quarks & 1 down quark, a neutron has 1 up quark and 2 down quarks. These quarks are bound together by gluons (and a bunch of virtual quarks, but don't worry about them for now).



      When a proton & electron react an up quark in the proton is converted to a down quark, and the electron is converted to a neutrino. This process is mediated by a $W^+$ boson. I can't find a good diagram of this exact process, but here's a diagram from Wikipedia of a closely related process: the decay of a neutron into a proton, electron, and antineutrino.



      neutron decay



      The diagram for the proton + electron reaction is very similar, just reverse the time direction, and swap the $W^-$ to a $W^+$, and the antineutrino to a neutrino.






      share|cite|improve this answer









      $endgroup$
















        7












        7








        7





        $begingroup$

        It's not exactly a myth that protons and electrons combine to form neutrons, but it's not very accurate. A proton and electron can react to produce a neutron, but a neutron isn't simply a composite particle consisting of a proton joined to an electron.



        Protons and neutrons are hadrons, which means they consist of 3 quarks. A proton has 2 up quarks & 1 down quark, a neutron has 1 up quark and 2 down quarks. These quarks are bound together by gluons (and a bunch of virtual quarks, but don't worry about them for now).



        When a proton & electron react an up quark in the proton is converted to a down quark, and the electron is converted to a neutrino. This process is mediated by a $W^+$ boson. I can't find a good diagram of this exact process, but here's a diagram from Wikipedia of a closely related process: the decay of a neutron into a proton, electron, and antineutrino.



        neutron decay



        The diagram for the proton + electron reaction is very similar, just reverse the time direction, and swap the $W^-$ to a $W^+$, and the antineutrino to a neutrino.






        share|cite|improve this answer









        $endgroup$



        It's not exactly a myth that protons and electrons combine to form neutrons, but it's not very accurate. A proton and electron can react to produce a neutron, but a neutron isn't simply a composite particle consisting of a proton joined to an electron.



        Protons and neutrons are hadrons, which means they consist of 3 quarks. A proton has 2 up quarks & 1 down quark, a neutron has 1 up quark and 2 down quarks. These quarks are bound together by gluons (and a bunch of virtual quarks, but don't worry about them for now).



        When a proton & electron react an up quark in the proton is converted to a down quark, and the electron is converted to a neutrino. This process is mediated by a $W^+$ boson. I can't find a good diagram of this exact process, but here's a diagram from Wikipedia of a closely related process: the decay of a neutron into a proton, electron, and antineutrino.



        neutron decay



        The diagram for the proton + electron reaction is very similar, just reverse the time direction, and swap the $W^-$ to a $W^+$, and the antineutrino to a neutrino.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered 9 hours ago









        PM 2RingPM 2Ring

        2,7632819




        2,7632819






























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