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Neutron production in (strong) magnetic field?

  1. Sep 22, 2015 #1
    I'm starting a new thread; it's not just about cyclotrons this time. The question is as follows: has anybody ever heard of or read about neutron production (=fusion reactions) when a beam of fuel nuclei, such as D+ or Li3+, is bent by a (strong) magnetic field, such as a bending magnet in an accelerator? The neutron production may not have been attributed to nuclear fusion, but people may rather have thought that it was due to spallation of the nuclei rather than actual fusion reactions.

  2. jcsd
  3. Sep 22, 2015 #2


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    Your question seems a little coy and vague. But oh well, onward.

    You can't get neutrons just from bending a beam in a magnetic field. You can only get it from collisions. So the beam has to hit something.

    When you get that situation there are lots of ways to get neutrons. Fission or spallation are each quite easy to produce. I would have to look up what reactions are easy to produce from these things hitting various targets. But I would guess that you could fairly easily get neutrons to spall out of a lead target with these. If the D's were fast enough and hit either D's or Tritium, you could probably get some fusion, which produces a toasty neutron. Again, I would have to look up what reactions are possible for Li, and what targets you would want.

    Lead can certainly spall neutrons when hit with neutrons. I would have to look up what it can do when hit by D or Li. But I'm guessing it can also spall from them. It's annoying because it means lead is not very satisfactory to shield from neutrons, especially if they start hot such as the 14 MeV neutrons you get from fusion of D-T.

    At least you can't get neutrons from bending in a magnetic field with any magnetic field humans are currently able to make. I suppose you could contemplate a magnetic field that changed abruptly fast enough to provide enough energy to pull the neutron out of a D. But certainly nothing humans have built can do that.
  4. Sep 22, 2015 #3


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    There is no sharp line between spallation and fusion. They can have very similar results, and splitting nuclear reactions in those two categories can be a bit arbitrary.

    The bending magnet has nothing to do with it. It can just influence where beam particles can hit other nuclei.
  5. Sep 22, 2015 #4


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    It's worth noting that the equality

    is not particularly true. For a couple of reasons: Not all neutron production is from fusion reactions (e.g. 9Be direct breakup, 9Be -> α + α +n) and not all fusion reactions result in neutron evaporation, or only neutron evaporation (e.g. fusion-fission, or fusion at low excitations resulting in a CN with excitations ~< 9 MeV, or fusion of light systems, which can result in p,α evaporation).
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