Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How do you create protons, neutrons, and electrons from energy?

  1. May 18, 2008 #1
    Quick question, regarding mass-energy equivalence (e=mc2) and matter creation.

    Knowing that there are many concete visual examples of matter turning into energy using Einstein's equation, how do you use energy to create matter? If I'm not mistaken, I beleive electron-positron pairs are created using photons, but how does one use energy to create protons and neutrons? What are the "energy ingredients" in this process? Thanks!
     
  2. jcsd
  3. May 18, 2008 #2

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    Gluons, and quarks.

    For instance in an electron-positron collider, you can create a quark-antiquark pair that undergoes hadronization and gluon emission -> in those processes protons and neutrons (and other hadrons) can be created.

    Also in a proton-antiproton collider and in a proton-proton collider, you will get free quarks and gluons that will undergo hadronization.

    In particle physics, a photon is a particle.
     
  4. May 19, 2008 #3


    Protons and neutron are created by a process called Pair production.
    Pair production refers to the creation of an elementary particle and its antiparticle via Quantum Chromodynamics (QCD).

    Pair production can only occur if the photon has an energy exceeding the twice the rest mass(me) of an electron (1.022 MeV); the same applies for the generation of other higher energy leptons such as the muon and tau.

    [tex]m_e = 0.00051099891844 \; \text{GeV}[/tex]
    [tex]m_p = 0.9382720298 \; \text{GeV}[/tex]
    [tex]m_n = 0.9395655681 \; \text{GeV}[/tex]

    [tex]E_{\gamma} = 2 m_e = 0.00102199783688 \; \text{GeV}[/tex]
    [tex]E_{\gamma} = 2 m_p = 1.8765440596 \; \text{GeV}[/tex]
    [tex]E_{\gamma} = 2 m_n = 1.8791311362 \; \text{GeV}[/tex]

    [tex]\gamma( E_{\gamma} ) \rightarrow \; e^+ + e^-[/tex] - Beta Pair production
    [tex]\gamma( E_{\gamma} ) \rightarrow \; p^+ + p^-[/tex] - Proton Pair production
    [tex]\gamma( E_{\gamma} ) \rightarrow \; n^+ + n^-[/tex] - Neutron Pair Production

    In semiclassical general relativity, pair production is also invoked to explain the Hawking radiation effect.

    Pair production is also the hypothesized mechanism behind the Pair instability supernova type of stellar explosions, where pair production suddenly lowers pressure inside a supergiant star, leading to a partial implosion, and then explosive thermonuclear burning.

    Reference:
    Pair production - Wikipedia
    Quantum chromodynamics - Wikipedia
     
  5. May 19, 2008 #4
    Two comments:

    - In particle physics energy is not an entity by itself but a property of particles. You do not turn energy into particles but you turn one collection of particles into another collection of particles where energy and momentum conservation dictate that both collections of particles have the same energy and the same momentum. The example of two photons (or one photon and some atom) turning into an electron-positron pair is not an example of energy turning into electron and positron but an example of a collection of particles (photon+X) turning into a different collection of particles (e+ + e-). Not related to what I wanted to say but for completeness: In the photon+atom reaction, the result is e+ + e- + atom; the atom remains in the final collection and merely absorbs some energy and momentum.

    - In theory there is (at least usually) not THE process to create some target collection. For example you can create an electron-positron pair not only with photons but also with different reactions, the simplemost being a Z-boson decaying into electron and positron. You don't find many (for any practical solution you could even say "you don't find any") Z-bosons naturally existing but there's quite some (in theory an infinite amount of) possible configurations that could create the Z for you, e.g. shooting a suitable lepton-antilepton pair or a suitable quark-antiquark pair onto each other. So if you happen to read collection X is created from collection Y, then it should in this context not be read as Y being the only collection that can create X but read as Y being the best-achievable, the most common (in nature or applications), the easiest to understand or perhaps the only experimentally used collection to create X.
     
  6. May 19, 2008 #5

    jimgraber

    User Avatar
    Gold Member

    trewsx7,
    As has been said here, our most common way of "creating matter" from energy via E =mc^2 is a particle collider. For instance you can have e + e and lots of kinetic energy go to e + e + p + n and lots of other particles. You can think of this as converting kinetic energy to rest mass, or "creating matter from energy".
    Jim Graber
     
  7. May 20, 2008 #6
    Matter creation from photons only occurs in close proximity to atomic nuclei. It is said that a sufficiently energy photon (>1.022 MeV) can cause the production of an electron and a proton just as is stated in the Wiki article on pair production.

    The question I have about matter creation in this process is: How do we know/decide/measure if one of the neutrons within the core has or has not been "annihilated" or "converted" into the "so-called" created matter (electron and proton) from the interaction of the gamma ray with the atom?
     
  8. May 20, 2008 #7

    Nice explanation of particles possessing energy.

    My question on this is: If energy is not an entity on its own, and light is massless, then what should I think light is, if it is not an entity on its own?
     
  9. May 20, 2008 #8

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    Energy is a property of a system, not an entity on its own. A car which runs 100 miles/h have energy, due to E^2 = p^2 + m^2.

    A photon have energy according to E^2 = p^2 + m^2

    A photon is in particle physics, a massless particle. A photon in classic electrodynamics is a wave.

    I have to quote my professor in Quantum mechanics: "An electron is an electron. It have wave properties, and particle properties. But it is neither of those. An electron is an electron".

    A photon/light is an entity on its own, and has energy. But there is no equivalence between light and energy. Light is (a form of) energy, but energy is not light.

    Also, that was a quite off-topic question of yours Bucky, I think we have some old threads about this question "what is energy?". Perhaps have a look at those, or make a new thread in the appropriate subforum.
     
  10. May 20, 2008 #9
    That's a process I'm not familiar with...

    Protons, neutrons and other hadrons are complicated composite particles. It's best to think of pair production of quarks and antiquarks, followed by a process of hadronization (see en.wikipedia.org/wiki/Hadronization for a start), as described by malawi_glenn.
     
  11. May 21, 2008 #10

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    The photon might be able to pair produce a quark - anitquark pair, that will undergo hadronization. But neutrons are composite objects in the standard model, so you're right.

    Orion1: Can you try drawing the Feynman diagram for the process:
    [tex]\gamma( E_{\gamma} ) \rightarrow \; n^+ + n^-[/tex]

    Also, what is a positive and negative neutron?..
     
  12. May 21, 2008 #11
    That's all I was saying :wink:. [tex]\gamma \to n + \overline{n}[/tex] through pair production and hadronization is fine by me.
     
  13. May 21, 2008 #12

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    what are the odds that only [tex] n + \overline{n}[/tex] are produced? There are thousands of possible hadronization channels.

    The photon must produce quark-antiquark pairs.
     
  14. May 21, 2008 #13
    True, but at least I know what those symbols mean!
     
  15. May 21, 2008 #14

    Correction, the reaction listed on Post #3 should be:

    [tex]\gamma( E_{\gamma} ) + N \rightarrow \; \overline{e}^+ + e^- + N[/tex] - Positron + Electron Pair production
    [tex]\gamma( E_{\gamma} ) + N \rightarrow \; p^+ + \overline{p}^- + N[/tex] Proton + Anti-proton Pair production
    [tex]\gamma( E_{\gamma} ) + N \rightarrow \; n^0 + \overline{n}^0 + N[/tex] Neutron + Anti-Neutron Pair production

    Above their respective threshold energies, these are the most probable pair production reaction types because of conservation of mass, charge and colour.

    My esteemed colleagues, being experts at conservation laws, will now demonstrate in the next posts what conservation laws this reaction violates:

    Universe Pair production:
    [tex]E_{\gamma} = 2 m_U[/tex] - Universe rest mass
    [tex]\gamma( E_{\gamma} ) + N \rightarrow \; U + \overline{U} + N[/tex] - Universe + Anti-Universe Pair production

    Reference:
    Universe - Wikipedia
     
    Last edited: May 21, 2008
  16. May 21, 2008 #15

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper



    What??

    Can you draw a feynman diagram for:
    [tex]\gamma( E_{\gamma} ) + N \rightarrow \; p^+ + \overline{p}^- + N[/tex]

    And a reference to an article about neutron-antineutron photon pair production.

    -From your wiki reference on Pair production:
    "Pair production refers to the creation of an elementary particle and its antiparticle, usually from a photon (or another neutral boson"

    Now a neutron is not an elementary particle, neither the proton.

    It is just not a matter of conservation laws, it is how particle interacts. Not everything that are ok with some conservation laws are physical.
     
    Last edited: May 21, 2008
  17. May 21, 2008 #16
    No, pion production and other hadronic states involving light mesons are far more probable than the latter two. As malawi_glenn points out, there are thousands of possible final states that can result from the hadronization of quark-antiquark pair production (the more fundamental process), all of which conserve energy, charge and colour. As a rough rule of thumb, processes with larger available phase spaces (lighter particles, generally) will be more likely.
     
  18. May 21, 2008 #17

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    try to get only two pions from quark-antiquark pair production... (A)
     
  19. May 21, 2008 #18
    I never said anything about only two pions, though I did gloss over the complications that phase spaces increase both with the number of particles and with their momenta, while increasing the number of particles reduces the momentum available to each. I think we're in agreement.

    PS. Is there any way to turn off the auto-linking to "momentum"?
     
    Last edited: May 21, 2008
  20. May 21, 2008 #19

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    Yes I know that we agree, just wanted to point that out for Orion1 :-)
     
  21. May 21, 2008 #20

    The reaction is two-Photon annihilation into baryon + anti-baryon pairs and it is the the most probable PAIR PRODUCTION reaction types because of conservation of mass, charge and colour.

    The fundamental reaction is:
    [tex]\gamma + \gamma \rightarrow q + \overline{q}[/tex]

    The Baryon + anti-baryon reaction is:
    [tex]\gamma + \gamma \rightarrow B + \overline{B}[/tex]

    The feynman diagrams are listed in reference 1.

    Universe Pair production:
    [tex]E_{\gamma} = 2 m_U[/tex]
    [tex]\gamma( E_{\gamma} ) + \gamma( E_{\gamma} ) \rightarrow \; U + \overline{U}[/tex] - Universe + Anti-Universe Pair production

    Reference:
    Two-Photon Annihilation into Baryon-Antibaryon Pairs
     
    Last edited: May 21, 2008
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: How do you create protons, neutrons, and electrons from energy?
Loading...