is possible some elements absorb neutrons, without any nuclear reaction?

Discussion in 'Physics & Math' started by StMartin, May 2, 2008.

  1. StMartin Registered Senior Member

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    Is possible some elements (like Cadmium or Bohr) absorb neutrons, without any nuclear reaction in their atomic nucleus? If the answer is YES, then why there isn't any nuclear reaction?
     
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  3. Vkothii Banned Banned

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    Isotopes have halo neutrons, that appear to pair up and have "extra-nuclear" orbits. Isotopes decay after a while.
     
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  5. Pete It's not rocket surgery Registered Senior Member

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    Neutron absorber
    There is a nuclear reaction, but the result is only to form a heavier, stable isotope of the same element.
     
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  7. StMartin Registered Senior Member

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    Do they decay after some period? Is there big energy released?
     
  8. Vkothii Banned Banned

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    No, it's the weak interaction. The decay half-life depends on the isotope's atomic number - how strongly coupled the halo neutrons are, presumably.
     
  9. StMartin Registered Senior Member

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    So, there is not any fission in the atoms of neutron abosorbers, right?

    But why there is such an "explosive" reaction in the atoms of uranium-235 or elements used for fission?
     
  10. Vkothii Banned Banned

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    Uranium is a much bigger nucleus, it decays differently to most isotopes (I think). Have a look at fission reactions, and isotope decay. Uranium fission involves alpha particles...?
     
  11. StMartin Registered Senior Member

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    Uranium fission involves slow neutrons.

    Is half-life decay same with nuclear fission?
     
  12. StMartin Registered Senior Member

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    What is their period of decay, after receiving the neutron? Are control rods inside nuclear power plants often replaced because of this?
     
  13. Vkothii Banned Banned

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    ...here you go:
    --wikipedia.org
     
  14. StMartin Registered Senior Member

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    But why they absorb neutrons? What is their half life period?
     
  15. Vkothii Banned Banned

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    Are you asking the half-life of a neutron? It's about 15 min, but that depends how fast it's going.

    Asking why neutron absorption is a little like asking why electron orbitals...? These things are "matter" particles that interact, is all. We explain interactions in terms of these things.
     
  16. StMartin Registered Senior Member

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    No, I am asking what is the half life period of the absorbers of neutron?
     
  17. Vkothii Banned Banned

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    Try finding a table of isotopes somewhere, that's what an element that's absorbed a neutron or two is. The periodic table is a list of stable isotopes, or "things that represent the same thing". I think that's what "isotope" means, but don't hold me on that.

    "Isotope is best used when referring to several different nuclides of the same element; nuclide is more generic and is used when referencing only one nucleus or several nuclei of different elements. For example, it is more correct to say that an element such as fluorine consists of one stable nuclide rather than that it has one stable isotope."

    ..is what the last edit in wikipedia reckons.

    P.S. regarding your original question, "nuclear reaction" can mean quite different things apart from fission or fissile elements.

    After all, electrons interact with nuclei, they're bound by the charge, of the nucleus.
    But with just the "boundary" of a nuclide, and considering halo neutrons which are there somewhere "near" the denser conglomeration of protons and neutrons, or a stable nuclide core, because of neutron capture.

    "One example of a halo nucleus is 11Li which has a half life of 8.6 mS. It decays into 11Be by the emission of an antineutrino and an electron. Its cross-section of 3.16 fm is close to that of 32S, a much heavier nucleus. Its radius is close to that of 208Pb. It contains a core of 3 protons and 6 neutrons, and a halo of two independent and loosely bound neutrons.

    Nuclei which have a neutron halo include 11Be and 19C. A two-neutron halo is exhibited by 6He, 11Li, 17B, 19B and 22C. Two-neutron halo nuclei break into three fragments and are called Borromean because of this behavior. 8He and 14Be both exhibit a four-neutron halo." - from wikipedia, again.
     
    Last edited: May 4, 2008
  18. StMartin Registered Senior Member

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    And why in Uranium-238, there is fission with fast neutrons, and it absorbs slow neutrons, how come that?
     
  19. Vkothii Banned Banned

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    Well, I think it has to do with potential states and barriers, or "allowed" states. For example, an alpha particle is tightly bound in a uranium nuclide, but somehow tunnels through the barrier, and alpha decay occurs - very slowly, but it's like there's a constant tension on this alpha particle, pulling on it elastically, and eventually - given sufficient time, the probability of it being on the other side of the barrier approaches unity.
    Probability is like that.
     
  20. StMartin Registered Senior Member

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    When Uranium-238 is attacked with fast neutrons, do it absorb it ?
     
  21. StMartin Registered Senior Member

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    And can I ask, how can we keep the neutrons, which want to escape, in the chain reaction? In my book says that it can be done by neutron caputre or neutron diffusion. I don't understand what they mean. PLease help! Thanks.
     
  22. Vkothii Banned Banned

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    You've asked about neutron diffusion elsewhere, haven't you?

    Try to imagine what "diffusion" might mean in terms of neutrons: things diffuse by separating, rather than gathering or concentrating, so neutron diffusion is related to neutron density - like the density of gases that mix together. It's also a term used in scattering experiments, but scattering is just "interaction angle".
    More scattered means - you guessed it - more diffused.
     
  23. StMartin Registered Senior Member

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    And how can we prevent losing neutrons with neutron capture?
     

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