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Concept of boson and fermion applied to atoms and more

  1. Jul 8, 2012 #1


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    Sometime I read that the helium atoms can be considered as boson, but I don't understand why. I know that its nucleous has a spin of 2 (integer) and that its 2 electrons gives the atom a total spin of 3, an integer.
    But then why isn't hydrogen considered also as a boson? I think it's considered as a fermion, like the electron itself. Why? The total spin of the H atom isn't 1 (thus an integer)? It seems like only the nucleous is the only important thing in deciding whether an atom can be considered as a boson or fermion, why is it so? And if I have a molecule, how do I determine whether it's a boson or fermion?
    In Wikipedia one can read
    and also
    where the enphasis is mine.
    Can someone explain me when I can call a particle/atom/molecule a boson?
  2. jcsd
  3. Jul 8, 2012 #2
    It depends on spin. Composite particles with an even number of fermions is a boson with integer total spin. Particles composed of an odd number of fermions is a fermion with half-integer total spin.

    A proton by itself is a fermion ( 3 quarks). A hydrogen atom has four fermions- 3 quarks and an electron- and is considered a boson.

    A hydrogen molecule (H2) consists of two bosons and is a boson.

    That wiki page should read particle.
    Last edited: Jul 8, 2012
  4. Jul 8, 2012 #3


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    Ok thank you very, very much! So in a way I'm either a fermion or boson. :tongue:
  5. Jul 9, 2012 #4
    I'm also wondering about something related. So hydrogen molecules are bosons. However, when they interact, do they behave as bosons? Why does liquid hydrogen not display superfluidity as helium, both the 3 and 4 versions do?

    Is there a size scale at which composite bosons no longer display the properties of bosons?
  6. Jul 9, 2012 #5


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    Hydrogen freezes before it can get superfluid.
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