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Efficient Neutron Sources

  1. Apr 8, 2015 #1
    Hi All,

    I have a basic question. I am still new to nuclear engineering so this maybe a stupid question, but what is the typical energy efficiency of a neutron source? (I.E. power of neutrons emitted/power input for neutron generation)

    I recognize that the efficiency can depend on the neutron flux, especially since the power loss does not scale linearly with the neutron flux, but what is the typical energy efficiency of a neutron source with a particle flux of 1E14 to 1E15 neutrons per square cm?

    Finally, how are these neutrons generated if controlled materials (like U-235 or Pu-239) aren't used? (like photoneutrons, neutrons from deuterium fusion, etc.)

    I'm interested because I want to try using a DIY neutron source to store electrical energy by transmuting Th-232 into U-233 and then burning that U-233 in a pile.
  2. jcsd
  3. Apr 8, 2015 #2
    The main types of neutron sources are isotopic (usually SF from Cf-252), nuclear reaction like (alpha,n), fusion (usually D-T or D-D), fisson reactors or spallation of neutrons from a charged particle beam hitting a target.

    This is a terrible idea. Fission = fission products = highly radioactive. Read up on the "nuclear boyscout" who did what you are proposing. Radiation safety is non-trivial and there is a reason that radioactive materials are regulated. Respectfully if you don't know how different neutron sources work I don't think you have the expertise to do this type of project safely (let alone legally). Nuclear has enough PR problems without DIY experiments going wrong.
  4. Apr 8, 2015 #3
    I have read about David Hahn but it didn't say what the radiation level he worked with. I do remember he had no protection against suspended powders and did not place the experiment in a glovebox. Also, he did not do the experiment under supervision of someone experienced with handling radioactive materials. I was planning on using very small levels of activity (30,000 to 300,000 Bq) to test the idea in a controlled environment (I.E. behind plexiglass and respirators) with the radiation safety officer at my local university. I do know fission products give off continual radiation, but to my understanding if the total activity is kept low, and its done behind a barrier that only miniscule amounts of radiation can pass through, its totally fine to work with.

    Now coming back to the neutron source question, what is the typical energy efficiency of spallation neutron sources? Or the D-D or D-T fusion sources? (I know that probably depends on reactor type and design)
  5. Apr 9, 2015 #4
    A Neutron Source emits Neutrons which are not easy to Shield. Typically large thicknesses Water, Borated Concrete, or paraffin are used since they have to be thermalized before they can be absorbed. Neutron Sources are typically Cobalt 60, Californium 256, or the like. They are high intensity and not readily obtainable. I would suggest that you apply to one of the DOE Associated University Labs for a project, to make this happen.
  6. Apr 9, 2015 #5


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    Neutron sources do not have an energy efficiency quantifiable in this way because they use the radioactive decay of some isotope to generate neutrons. Although you could perhaps quantify its fuel efficiency, such a value would be mostly meaningless in this context.

    The energy efficiency of a Farnsworth Fusor would be extremely low - you need many kilowatts of power to generate small fluxes.

    That flux level would be on par with a 2 MW TRIGA research reactor at full power. A nuclear reactor does not have an energy efficiency, it is generating its own energy, and neutrons.

    The only way to create neutrons without a radioactive source would be a Fusor type device. Which would be extremely energy inefficient in terms of joules/neutron.

    You aren't describing "storing electrical energy" in any sense. You are describing a sub-critical nuclear reactor, which if powered by a Fusor neutron source, would be extremely energy inefficient. Meaning spending something on the order of 10 kilowatts of energy to get maybe a nanowatt of fission power back.
  7. Apr 11, 2015 #6

    jim hardy

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    Sounds like a breeder to me.

    It doesn't take very many neutrons to hurt you. This thread could fall under PFs "dangerous activities"

    I can see that your science is basically okay
    but you have no appreciation for scale. That'll come with experience.
    10^14 is roughly the flux at center of a PWR power reactor. You want twenty feet of concrete between you and that sort of flux.

    Here's what 10^12 nv does to water
    in my student days i measured flux in that little reactor by inserting copper wires into the core for a few seconds, then measuring how much they'd got activated.
    Sometimes i had to let them "cool off" for a day before handling them.
    As an undergrad i was well supervised.

    Take a course in Reactor Operation if your school has one.
    And don't be making neutrons in your kitchen.

    good luck in your studies.

    old jim
  8. Apr 11, 2015 #7


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    Not without a approval and a license (authorization) from the US NRC, and concurrence with state government. One is talking about utilization (and production of neutrons) of special nuclear material. One does not DIY!

    Typical non-fission neutron sources have neutron production rates that are fractions of a fissile source. Non-fissile neutron sources are used to produce detectable levels of neutrons when fission systems are 'shutdown', although some neutron sources do use 'spontaneous fissions' of transuranic nuclide. A flux of 1014 n/cm2-s and greater is pretty high, and that would mean lots of shielding.

    Transmuting Th-232 to U-233 is a special process requiring a reactor system, and that requires licensing by the US NRC.
    Last edited: Apr 11, 2015
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