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Neutron beams

  1. Nov 9, 2014 #1
    DISCLAIMER: This thread is a repost of another thread in the Nuclear/Particle Physics forum since I cannot delete that thread but this forum is more appropriate since it is more of a question in Nuclear Engineering than in Nuclear Physical theory.

    So I have been reading about the operational principles of compact neutron generators(which use fusion, either D-D or D-T). And apparently all of the types mentioned generate isotropic neutrons by accelerating deuterium ions into a target containing lithium deteuride or a metal plate coated with tritium. Now I also realize that neutrons, having a magnetic moment, can be deflected and focused into a beam using a hexapole magnetic lens.
    So So this is the question I have for you experimental nuclear physics wonks: If a neutron source like the one I described has the deuterium beam target enclosed in a cylindrical magnet with an antiparallel magnetic field, does the constraint of the magnetic field have any effect on the direction of neutron emission? That is, can this technique be used to force neutrons emitted from the fusion reaction to flow outwards away from the target plate instead of isotropically in all directions? If this does not work, how else can a focused beam of neutrons be produced so that they can be collimated into a directional beam?
     
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  3. Nov 9, 2014 #2

    Astronuc

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    Orienting the spin of a neutron and directing the path of a neutron are two completely different things. Neutrons are not deflected in a magnetic field, or if they are, it's extremely weak - after all, neutrons are neutrally charged.

    A neutron beam is developed by collimating a source, that is usually isotropic.
     
  4. Nov 9, 2014 #3

    Finally the answer I've been looking for!

    In that case, for a compact neutron tube that generates neutron by colliding deuterons with LiD coated target one would need a neutron reflector(like Beryllium)that would bounce the neutrons flowing backward and perpendicular to the direction of deuteron flow in the forward direction and then use a hexapole magnet collimator.
     
  5. Nov 9, 2014 #4

    Astronuc

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    No, high energy neutrons do not bounce back. Fusion and fission neutrons are in the MeV range, with dt-produced neutrons having an energy around 14.1 MeV. They usually scatter with small angles, or at least angles less than 90 degrees. A fast neutron could conceivably hit a proton spot on and lose all it's energy, but it's not going to bounce backward, except possibly with the energy of the struck proton.

    Thermal neutrons in equilibrium with their environment can be scattered backward, or upward in energy, and cold neutrons could be knocked backwards, but one would lose a lot of neutrons while slowing down, unless one had a low cross section material, like liquid He.

    Their is some anisotropy with a deuteron beam on a target of d or t, but likely the incident energy of the deuterons is in the 5-100 keV range compared with MeV range of the fusion induced neutrons.
     
  6. Nov 10, 2014 #5
    What I'm also asking about is if there is any evidence for the possibility of generating anisotropic neutrons in the energy ranges you mentioned from fusion by means of a D-D accelerator fusion.

    Actually, I did my homework through google by searching for "anisotropic neutron emission" and found this. So I'm not sure if this device actually works and if its efficacy has been established by the principle involves magnetic alignment of the spins of the accelerated deuterons and the deuterium or tritium atoms in the deuteron beam target.
     
    Last edited: Nov 10, 2014
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