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Neutrino flux

  1. Oct 9, 2008 #1
    Regardless of the measured flux, is the expected neutrino flux from the sun greater or less than the expected flux from nuclear reactors? I don't know if I'm using the word flux correctly. I mean number of neutrinos per square meter per second on the surface of the earth.
    Last edited: Oct 9, 2008
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  3. Oct 9, 2008 #2
    Neutrino flux from the sun is constant and neutrino flux from a nuclear reactor is inversely proportional to the square of distance. The flux from a typical reactor falls below the solar flux at the distance of a few hundred meters.

    Also, it's worth mentioning that sun produces neutrinos and nuclear reactors produce antineutrinos.
  4. Oct 10, 2008 #3
    Thanks hamster143.

    Neutrino flux from the sun should also be inversely proportional to the square of distance and the distance from the Earth to the Sun is not constant.

    Is it correct to assume that an experiment could be conducted close enough to a reactor so that the expected flux from the sun would be dwarfed by the flux from the reactor, say less than 5%? Specifically, I am interested in the effect of neutrinos on the half lives of atomic nuclei.
  5. Oct 10, 2008 #4


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    Have you tried google?
    I got many answers to your question using google in 2minutes.
  6. Oct 10, 2008 #5
    Thanks for the suggestion malawi_glenn. I got a bunch of reports about neutrinos being produced by the decay of nuclei. I'm looking for the opposite effect. What was your google query?
  7. Oct 10, 2008 #6


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    you mean "neutrino capture" or "inverse beta decay by neutrinos" (same thing, different names, altough what is usally meant my inverse beta decay is a nuclei capturing an electron or positron, producing a neutrino)

    You can google "solar neutrino flux" ,"reactor neutrino flux", "neutrino capture", "inverse beta decay", "The Reines-Cowan Experiments" (the first discovery of the neutrino) ,"solar neutrino production", "neutrino production", "Artificially produced neutrinos"

  8. Oct 10, 2008 #7
    What I am looking for is the effect on nuclear half lives of the presense of a flux of neutrinos. Of course, everything on earth is in the flux from the sun. Given that the flux from a reactor could potentially overwhelm the flux from the sun, I wonder if there is some experiment that has been done that exposes nuclei to the flux from a reactor. By simply moving the experiment closer and further away from the reactor, the amount of flux could be controlled and the half life could be shown as a (possibly constant) function of neutrino flux.
  9. Oct 10, 2008 #8


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    Well you can read about every neutrino experiment underground using reactors done so far to read about neutrino flux from sun vs. neutrino flux from reactor, then see if any experiment you are looking for has been done.

    What you basically is after is neutrino capture crossection of nuclei...
  10. Oct 10, 2008 #9
    The distance from the Earth to the Sun is, for all intents and purposes, constant. The primary effect (eccentricity of Earth's orbit) is on the order of 6%.

    Like I said, sun produces neutrinos and reactors produce antineutrinos, so you may see two independent effects due to one and the other.

    The very first experiment that proved the existence of antineutrinos was done at the reactor site, 11 m from the reactor.


    Neutrino-nucleus cross section is tiny. They were seeing three events per hour in 200 kg of water at 1000x the solar flux.
  11. Oct 10, 2008 #10
    Thanks again hamster143. Whether it is considered constant depends on the intents and the purposes. As I am interested in the square of the distance, am I correct that the effect would be on the order of .06 * .06 = .0036? Is a variation of this magnitude in the half-lives of nuclei measurable? Here is what I have in mind. First, establish the functional relationship between neutrino flux and half-life in experiments near a reactor. Vary the distance from the reactor in order to vary the neutrino flux. Once you know the function, apply it to seasonal fluctuations in half-lives. Perhaps this would provide a measure of solar neutrino flux.
  12. Oct 10, 2008 #11
    No, the variation of distance is 0.03 , the variation of flux is (1.03^2 - 1) ~ 0.06.

    But the effect on half-lives will likely be many orders of magnitude smaller, because it also depends on cross section.

    To give you an idea:

    Uranium 238 is a relatively stable isotope, with half-life of several billions of years. In a kilogram of uranium 238, there are 12,000 spontaneous decays per second.

    If uranium 238 can capture antineutrinos with the same cross-section as hydrogen in water, you can place that kilogram of uranium within 10 m from a nuclear reactor and it would only induce one additional decay every 10 hours. That effect is obviously so tiny that it's not even measurable.

    You seem to be suggesting that maybe the effect of neutrinos is much higher. You can try to verify that by setting shop near the reactor. Part of the problem is, in addition to neutrinos, reactors produce all other kinds of radiation. For example, neutrons.

    Instead of measuring half-life, you want to measure decays per second. Set up a system with a quantity of radioactive material, a Geiger counter, and some shielding. Uranium-238 (aka depleted uranium) is relatively easy to obtain. Put the whole system into a lead box to block cosmic rays and such, load it into a car. Find a nearby nuclear reactor. I don't know where you live. Here in Southern California, one can legally get within a couple hundred meters from the San Onofre reactor.
    Last edited: Oct 10, 2008
  13. Oct 10, 2008 #12
    Thanks again for all your help. I won't be conducting any experiments in the near future. However, perhaps there are some experimental physicists who have experience, access to resources, sensitive detection equipment, lab coats, etc., and clearance to set up shop near a reactor who could look for and measure the effect.
  14. Oct 11, 2008 #13


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    If you seriously want to encourage physicists to do this experiment, you need to write up a solid paper and get it published in a peer-reviewed journal, give presentations about it at conferences, etc. You have to give them some reason for doing it, i.e. some theory which predicts that they should see something, and makes some mathematical connection between parameters of the theory and the (hypothetical) measured effect.

    A web forum like this one has practically zero weight in influencing research.
    Last edited: Oct 11, 2008
  15. Oct 11, 2008 #14

    Does anyone actually know what the solar neutrino luminosity value is?

    I am searching for a power equation in SI Watts.

  16. Oct 11, 2008 #15
    This is catch-22 jtbell. I can't write up a solid paper and get it published in a peer-reviewed journal, give presentations about it at conferences, etc. any more than I can conduct the experiment myself. This forum may be a poor venue to spark curiousity, but it's all I've got.

    Here is a paper in arxiv from which my questions arise. The authors mention a possible effect of neutrinos on half-lives, but without saying so, they seem to be unaware if such an experiment ever took place. I'm curious to know if there has.

  17. Oct 12, 2008 #16


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    Here are some energy spectras, can find you more if you want. Have quite many pdf's on my computer.

    You should be able to work out the luminosity by knowing the flux of neutrinos at surface of the earth.
  18. Oct 12, 2008 #17


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    Of course neutrinos should affect nuclear half lives, but whether such experiment has been performed or not I can't promise you.
  19. Oct 12, 2008 #18


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  20. Oct 13, 2008 #19
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