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A Bose-Einstein condensate of alpha particles

  1. Nov 8, 2005 #1
    Is it possible to make a Bose-Einstein (or Fermi-Dirac) condensate out of alpha particles alone? In other words, is the effective size of a nucleus, like that of a neutral atom, substantially affected by supercool temperatures?
     
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  3. Nov 9, 2005 #2

    mathman

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    I believe there would be serious practical difficulties. The electric charges would tend to make the aggregation of alpha particles (almost?) impossible.
     
  4. Nov 9, 2005 #3

    Gokul43201

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    I'm not sure I understand how the second question is the same as the first (or even how they are related). Could you explain what you mean by that ?
     
  5. Nov 9, 2005 #4
    Consider a Bose-Einstein condensate. The effective radii of its electron orbits are vastly increased over those of typical matter, but is the size of its nuclei likewise enlarged?
     
    Last edited: Nov 9, 2005
  6. Nov 10, 2005 #5

    Haelfix

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    I very much doubt you could ever make one, even in principle. The dipole moments and other higher order effects would tend to dramatically decrease the phase space for the requisite superposition amplitudes, making it vanishingly improbable.
     
  7. Nov 10, 2005 #6

    ahrkron

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    A BE condensate is usually made out of neutral particles, so I imagine here you are assuming that each of them is an atom.

    When you mention the "electron orbits", I imagine you are talking about the electrons of each atom composing the condensate. why would these electrons' orbits be increased? actually, I think the contrary would be true, since each particle of the condensate (each atom in this case) would be in its lowest energy state.
     
  8. Nov 10, 2005 #7

    ZapperZ

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    I think this is why Gokul was confused (and frankly, so was I). A question on "alpha particles" that includes "electron orbits"/atoms just don't mix well.

    Zz.
     
  9. Nov 10, 2005 #8
    Atoms in a B-E condensate are considered to be effectively many times their size as measured at room temperature, yes? I was wondering whether nuclei underwent a similar effect. Forget the alpha particles, think of an atomic nucleus, e. g. that of helium. Is its change in extent (uncertainty) significant when lowered to ultracool temperature? Maybe I should consider the mass of the electrons vs that of the nucleons.
     
  10. Nov 10, 2005 #9

    ahrkron

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    Can you provide a reference to that? I've been far from this kind of material for a long time. What are you referring to as their "effective" size?
     
  11. Nov 10, 2005 #10

    ZapperZ

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    There are very strange statements in here that make this very puzzling.

    Zz.
     
  12. Nov 10, 2005 #11

    mathman

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    It sounds like there is a lot of confusion here. You cannot make a B-E condensate out of charged particles (alpha particles and He4 nuclei are the same thing and are charged).
     
  13. Nov 10, 2005 #12
    Perhaps this will help explain the concept of "effective size increase" during the formation of a Bose-Einstein Condensate....
    At this web site by physicists Eric Cornell & Carl Wieman:
    http://www.fortunecity.com/emachines/e11/86/bose.html
    they explain how, ..."as a collection of atoms becomes colder, the size of the wave packet grows"...
    When individual atoms are sufficiently cooled, their wave packets begin to overlap, and when they reach the lowest possible energy state allowed by HUP, they coalesce into a single "macroscopic" wave packet, what is called the Bose-Einstein condensate.
    Now, as to the question of the thread, we can consider the alpha particle to be two [NP] deuterons each with unique wave functions bound to form {[NP]+[NP]}[also called Helium-4], this is predicted by a variety of cluster models of the atomic nucleus such as the Pauling Close Packed Spheron Model, the John Wheeler Resonating Group Method model, the Brightsen Nucleon Cluster Model. If then, we cool a collection of alpha particles, it would be predicted from the above statements by Cornell & Wieman that the wave packets of each [NP] cluster would increase in size, and when the lowest possible energy state is reached as allowed by HUP for Helium-4, it would seem to me that at least in theory, it may be possible to form a Bose-Einstein condensate, if we assume Helium-4 is composed of fundamental [NP] clusters as predicted by cluster models.
     
  14. Nov 10, 2005 #13

    ZapperZ

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    Being a "macro" particle does not mean that each of the atom/particle/whatever has increase its size. It is STILL the same particle, but now it has acquired a PHASE COHERENCE with other particles in such a way that a single state describes all of them.

    Secondly, as mathman has state, we do not have bare charged particles forming a condensate. The ONLY example we have so far are the formation of Cooper pairs of bound electrons in superconductors. But these can only occur due to the presence of an external "glue", such as phonons, that provide the mechanism for the formation of such pair. Free electrons in vacuum does not form any BE condensate. And I would venture that this would be even worse for alpha particles that has double the charge and a gazillion times larger in size.

    Zz.
     
  15. Nov 10, 2005 #14
    OK, can the wavefunctions of supercooled helium nuclei (not free alpha particles) overlap (phase cohere) like those of the helium electrons? Consider the temperature TN=(Me/MN)Te where the masses are those of an electron (e) and nucleon (N), and the temperatures those where the respective wavefunctions cohere proportionately. This follows from the Heisenberg uncertainty principle.
     
  16. Nov 10, 2005 #15

    Gokul43201

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    Note : It is possible to have a Bose gas of charged particles in high magnetic fields. Alexandrov has written several papers on this subject.
     
  17. Nov 10, 2005 #16

    ZapperZ

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    Again, what you have said here made very little sense. It's a hodge podge of disjointed concepts put together.

    Zz.
     
  18. Nov 10, 2005 #17

    ZapperZ

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    But we have no evidence of that so far, Gokul. The only evidence I have of the use of an external magnetic field to help in the BE condensation was the one from last year where fermionic atoms form Cooper-type pairing with the help of external magnetic field to allign their spins. Such things are certainly possible at the BEC-BCS crossover region since there's no coulombic repulsion to overcome.

    Zz.
     
  19. Nov 11, 2005 #18
    If you read the web link I cite from my post #12 on this thread, the use of magnetic fields as a second step to form a BE condensate (after a laser first step) is outlined, and I copy the text below in italics:
    To get around the limitations imposed by those random photon impacts, we turn off the lasers at this point and activate the second stage of the cooling process. This stage is based on the magnetic-trapping and evaporative-cooling technology developed in the quest to achieve a condensate with hydrogen atoms. A magnetic trap exploits the fact that each atom acts like a tiny bar magnet and thus is subjected to a force when placed in a magnetic field . By carefully controlling the shape of the magnetic field and making it relatively strong, we can use the field to hold the atoms, which move around inside the field much like balls rolling about inside a deep bowl. In evaporative cooling, the most energetic atoms escape from this magnetic bowl. When they do, they carry away more than their share of the energy, leaving the remaining atoms colder.
    The analogy here is to cooling coffee. The most energetic water molecules leap out of the cup into the room (as steam), thereby reducing the average energy of the liquid that is left in the cup. Meanwhile countless collisions among the remaining molecules in the cup apportion out the remaining energy among all those molecules. Our cloud of magnetically trapped atoms is at a much lower density than water molecules in a cup. So the primary experimental challenge we faced for five years was how to get the atoms to collide with one another enough times to share the energy before they were knocked out of the trap by a collision with one of the untrapped, room-temperature atoms remaining in our glass cell.
    Many small improvements, rather than a single breakthrough, solved this problem. For instance, before assembling the cell and its connected vacuum pump, we took extreme care in cleaning each part, because any remaining residues from our hands on an inside surface would emit vapours that would degrade the vacuum. Also, we made sure that the tiny amount of rubidium vapour remaining in the cell was as small as it could be while providing a sufficient number of atoms to fill the optical trap.
    Incremental steps such as these helped but still left us well shy of the density needed to get the evaporative cooling under way. The basic problem was the effectiveness of the magnetic trap. Although the magnetic fields that make up the confining magnetic "bowl" can be quite strong, the little "bar magnet" inside each individual atom is weak.This characteristic makes it difficult to push the atom around with a magnetic field, even if the atom is moving quite slowly (as are our laser-cooled atoms).
    In l994 we finally confronted the need to build a magnetic trap with a narrower deeper bowl. Our quickly built, narrow-and-deep magnetic trap proved to be the final piece needed to cool evaporatively the rubidium atoms into a condensate. As it turns out, our particular trap design was hardly a unique solution. Currently there are almost as many different magnetic trap configurations as there are groups studying these condensates.
     
  20. Nov 11, 2005 #19

    ZapperZ

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    I'm sorry, but how does this address the comment I did to your post? I know about magnetic cooling. It's covered in every undergraduate thermo text and courses. What you have laboriously cut and paste is a handwaving description of magnetic cooling. This does not do anything in terms of the physics of BE condensation. The fermionic gas that formed the be condensate did not use the external field to "pump" heat out of the gas, but rather use it as the external glue for the pairing formation. This is a completely different animal.

    Zz.
     
  21. Nov 11, 2005 #20
    With all due respect since I have little knowledge of how BE condensates are formed....the web link I cite does (at least to me) suggest that the pumping out of the heat (for the Rh atoms they worked with) requires the presence of BOTH an external magnetic field, plus a cooling source, unlike the Cooper Pairs of electrons example you cite. That is, the magnetic field is "required" to allow the heat to be pumped out of the Rh atoms they worked with to allow them to form a BE condensate, that is, no external magnetic field, no cooling of Rh atoms to form BE condensate possible.
    Also, Helium-4 (the alpha) is a boson (spin = 0) not a fermion, and thus in theory (I think) should follow Bose-Einstein statistical dynamics that would allow a BE condensate to form. The Pauli exclusion rule would not apply to packing as many Helium-4 bosons into a single energy level as one wishes. But please do correct my errors.
     
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