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B High energy protons and electrons to gamma radiation

  1. Aug 31, 2016 #1
    Can high energy incoming protons and electrons be absorbed and their energies remitted by photons? If so what are the typical ranges of energies emitted and are they heading in the same direction as the original emission if we had a sheet of metal being bombarded by those protons and electrons?
  2. jcsd
  3. Aug 31, 2016 #2


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    They form particle showers, including photons but also other particles. Electrons produce electromagnetic showers, protons produce hadronic showers.
  4. Aug 31, 2016 #3


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    the basic possible interaction between an electron and a proton is the inverse beta decay, where the result is a neutron and an electron neutrino. It also happens spontaneously within some atoms (electron capture).
    In general protons and electrons cannot give just photons. Hadrons (such as protons) must be color neutral. By erasing a quark out of them (to annihilate with the electron) would result to a non-color neutral state... so indeed they give hadronic showers instead (which of course could additionally produce photons, eg the neutral pion decays). But there is a stronger reason:
    Now if you say "ok, I cannot erase one thing at a time, could I erase the whole proton at once?" again the answer is no. In fact the interaction:
    [itex]e + p \rightarrow \gamma + \gamma[/itex]
    is forbidden in the Standard Model of Particle Physics by the conservation of Lepton and Baryon Numbers...at the left hand side you have electron lepton number +1 while on the right hand side you have 0... similarily for the baryon number.
  5. Sep 1, 2016 #4
    On the other hand, high energy electrons hitting matter do emit their energy as photons, called x-rays but indistinguishable from gamma rays. They do not cease to exist, but they do stop in the electrode and are absorbed by electrode, becoming indistinguishable from the electrons that already were in Fermi sea.
  6. Sep 1, 2016 #5
    The answers up to now are all well and good, and personally really do say where the energy goes, however I would like to know, the radiation comes from one uniform direction onto say a plate, how much deflection should we see, if occurs, as in, electrons and protons come in a velocity vector parallel to the x axis towards the positive values of x and hit the plate, would the radiation continue the same trajectory it had before or some would be deflected?
    and what dictates this deflection (not on atom by atom scale, but the material being hit as a whole)?
  7. Sep 1, 2016 #6
    In a x-ray tube, where electron energies are small compared to rest mass of electrons and of target nuclei, photons are generally emitted in roughly all directions, and photons in unwanted directions are absorbed.
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