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Free Neutrons - What interacts with them?

  1. Jan 8, 2007 #1
    Hey, I was wondering about possible interaction with free neutrons and if any have been seen experimentally. Here is a quote from hyperphysics:

    'A free neutron will decay with a half-life of about 10.3 minutes but it is stable if combined into a nucleus.'

    Can a photon interact with the free neutron before it undergoes its weak interaction decay?
     
  2. jcsd
  3. Jan 8, 2007 #2
    Hi order, it is possible for a photon and a neutron to interact. The neutron is electrically neutral and so low energy photons would not do the job. However, when the photons have high enough energy they can "see" the quarks that the neutron is composed of. Quarks do have electric charge and so interact with photons.
     
  4. Jan 8, 2007 #3
    The neutron also has a magnetic moment, weak though it is, so it will also interact through that mechanism. In fact, you can measure magnetization transitions using neutron scattering in this way.
     
  5. Jan 9, 2007 #4

    vanesch

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    The main interaction of (slow) free neutrons before decay is with certain nucleae, often through the strong interaction. This can be capture, (in)elastic scattering or genuine nuclear reactions. For instance, there is a big interaction cross section with Boron-10, Helium-3, lithium-6,gadolinium-157,-uranium-235, and these reactions are often used in a thermal neutron detector, because the reaction products are electrically charged and quite energetic, so easily detected by an ionisation-sensitive detector (charge collection, scintillation...).
     
  6. Jan 9, 2007 #5

    ZapperZ

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    Er... free neutrons are the ones that intract with uranium nuclei to initiate fission in our nuclear reactors. So yes, they can interact.

    Zz.
     
  7. Jan 9, 2007 #6

    disregardthat

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    Doesn't the neutron react with the uranium nuclei, and not a photon in nuclear reactors?
     
  8. Jan 9, 2007 #7

    ZapperZ

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    Who is addressing "photon" in nuclear reactors?

    Zz.
     
  9. Jan 9, 2007 #8

    disregardthat

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    The thread starter?

    He doesn't ask if the neutron interpheres with the nucleus, he asks if the neutron can interact with a photon.
     
  10. Jan 9, 2007 #9

    ZapperZ

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    Yeah, but in a nuclear reactor? I was the one who brought up the example in a nuclear reactor. The OP only wanted to know if neutrons interact with anything, and brought up a question of neutron interacting with a photon.

    Zz.
     
  11. Jan 9, 2007 #10
    Yes, you are both right. I first asked whether the free neutron could interact with anything, but then specifically asked whether a photon would interact with it. I should have wrote the fission example into my question as one example, since its the easy obvious one.

    My question was flawed, not your responses. I guess I really just wanted to know if a photon interacts with a free neutron, so then?
     
  12. Jan 9, 2007 #11
    Great answer Varn, ty.

    Maybe you can help me understand why Cadmium is such a good neutron absorber (ie. cadmium control rods in nuclear reactors)...
     
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