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Are photons affected by the strong force? The weak force?

  1. May 22, 2009 #1
    Can light travel through an atom? If yes, how will it emerge? If no, why not? Will it interact with any subatomic particles?
     
  2. jcsd
  3. May 22, 2009 #2
    I'm inclined to believe that photons, being the electromagnetic force carriers, aren't affected by any other forces. but then, this is not really my field. haha, excuse the pun.
     
  4. May 22, 2009 #3
    hahaha. I'm still a novice at physics, but i'm fascinated by it, and questions like these just seem to pop up into my head every now and then, for no apparent reason! Anyways, I thought photons might be affected by the electrons in the atom, as they might increase the electrons' energy to throw them out of the atom... photoelectric effect, anyone? But, assuming that the incident photons on an atom do manage to make it past the electron cloud without interacting with them, how would they react when they hit the nucleus?
     
  5. May 22, 2009 #4
    Many nuclei have photonuclear reactions, such as (photon,neutron) or (photon, alpha particle). For example, photons above about 20 MeV on oxygen-16 will knock a neutron out, leaving radioactive oxygen-15. The cross section is typically a few millibarns.
    For comparison, the nuclear size (radius) for oxygen is about R=1.3A1/3 x 10-13 cm = 3.2 x 10-13 cm, so geometric area = 0.33 barns.
     
  6. May 22, 2009 #5

    diazona

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    Yeah, but that's an electromagnetic interaction. Photons are not affected by the strong force.

    I think they would be affected by the weak force, since the W bosons (carriers of the weak force) are charged. I don't know enough offhand to describe that in detail, though.
     
  7. May 22, 2009 #6
    if the energy levels were high enough the electromagnetic and weak forces would unify, so it wouldn't be surprising if, in those conditions, and photon could conceivably be affected by the... well not really weak force, rather the elctroweak force
     
  8. May 23, 2009 #7

    malawi_glenn

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    Photons will not interact with those at these energy scales though, this is why one needs electroweak unification at very very high energies.
     
  9. May 23, 2009 #8

    malawi_glenn

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    photoelectric effect is not a atomic reaction, but a reaction in a solid where the electrons behaves as a collective.

    Here are some resources

    http://www.ndt-ed.org/EducationResources/CommunityCollege/RadiationSafety/theory/interaction.htm

    http://www.sciencemadness.org/lanl1_a/lib-www/la-pubs/00326397.pdf
     
  10. May 23, 2009 #9

    Vanadium 50

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    Of course it can. Can you see through glass?
     
  11. May 23, 2009 #10
    okay, so light travels through an atom.... let's go deeper into it. How? I want to know exactly how it passes through an atom... does it just go straight through the nucleus and the electrons, without anything affecting it? or does it pass through the vacuum inside an atom? Does it travel in a straight path? Is there any reflection/refraction/deviation?


    Yes, we can see through glass. If the answer was this simple, i wouldnt have posted it in the quantum mechanics section :biggrin: We can see through glass... then why cant we completely see through a photographic plate, or butterpaper, or a diamond?
     
  12. May 23, 2009 #11

    malawi_glenn

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    i) In QM, photons do not go straight lines, we don't have defined paths in quantum mechanics. Particles are not tiny tiny balls, and the atom is not a tiny tiny solar system. Photons do not "travel through atoms"

    ii) Interactions and processes are deterministic, the photon has a certain probability to interact with the atom/electron/nucleus. The probability is a function of energy and material etc.

    iii) Interactions in matter is not atomic feature but solid, the electronsm behave as collective -> constituting a energy band (in atom we have energy levels/lines)

    What you are asking doesn't make sense in a QM point of view. In QM sense we have two basic ingredients: 1) probability of outcome 2) energy bands

    Glass have an energy band in the optic spectra, wheras some other material don't.
     
  13. May 23, 2009 #12
    I did anticipate an answer like this :P So then, what field does this question make sense in? Is it even possible to answer my question using QM?
     
  14. May 23, 2009 #13

    malawi_glenn

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    yes QM, but in QM we don't have particles traveling around like tiny balls...
     
  15. May 23, 2009 #14
    okay, explain it using the QM model with waves, and the energy/material uncertainty, or whatever it is...
     
  16. May 23, 2009 #15

    malawi_glenn

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    i just told you the basics, the photon has a probability to interact with matter as a function of its energy.
     
  17. May 23, 2009 #16
    Photons can knock an electron out of a single atom of gas, with the only final state components being a photoelectron, and a recoil ionized atom. One example would be a 15-eV UV photon ionizing a gaseus hydrogen atom, with a photoelectron and a recoil proton in the final state.
     
  18. May 23, 2009 #17
    Can light travel through an atom? If yes, how will it emerge? If no, why not? Will it interact with any subatomic particles?

    Good question. Simple questions often have no simple answers. This is one. One could possibly write a book in reply. If you are looking for a purely quantum mechanical explanation read no further as I don't know theoretical QM at that level of detail. Your question is posed in classical terms but is under QM so I'm not sure if you realize the overlap between different fundamental theories. Quantum field theories for the strong nuclear force and the weak nuclear force have been developed, the former called quantum chromodynamics and might be of interest to you.

    A classical analogy would be to ask "does light travel through the earth sun complex?" think of the sun as the nucleus the earth as an electron....atoms are 99% (illustrative number only) empty like this system. so usually light DOES usually pass through an atom in this sense...it passes through the "vacuum" as you posted. (but it is NOT a vacuum). And the phton NEVER goes exactly STRAIGHT through because each photon IS deflected every so slightly by gravity...say of the nucleus, but that's not measureable.

    Another reasonable answer is that photons interact with materials (atoms) in a number of different ways which depends both on the energy of the photon and the nature of the material. Some materials reflect most light , others are translucent like glass (pass most light) yet can also "bend" (focus) light like a concave glass lense, other materials are opaque and others exhibit the photo electric effect. Each affects light (photons) a bit differently.
    In quantum mechanics, since a photon is likely to bring an atom into a firm state if it wasn't already ( collapsing the wave function in one interpretation) likely the photon can't "travel through" in the classical sense, but the actual result as noted by others is statistical in nature.

    The strong force affects quarks, the weak force radioactive decay, the electromagnetic force charged particles; a photon is none of these but IS affected by the gravitational force. See gravitational lensing which CAN be measured.

    You can also look up COMPTON SCATTERING in wikipedia, for example, for related interactions...and note the wave particle duality....
     
    Last edited: May 24, 2009
  19. May 24, 2009 #18

    malawi_glenn

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    But that we call Ionizing ;-)
     
  20. May 24, 2009 #19
    In some (most) physics books, photon scattering off an electron (with a photon in final state) is called Compton scattering, and photoelectric when there is no secondary photon. Accelerator builders are now acceleratiing H-minus beams; a single proton with two electrons. The H-minus atom has charge of minus one. A 2-eV photon (red laser) can knock off one electron, leaving a photoelectron and a neutral hydrogen atom. Would you call this a de-ionizing reaction? See
    http://neutrons.ornl.gov/aboutsns/how_sns_work.shtml [Broken]
     
    Last edited by a moderator: May 4, 2017
  21. May 25, 2009 #20

    malawi_glenn

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    What is the difference of photoelectric effect and ionization then?
     
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