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Positive charge atomic form-factor

  1. Yes, I have.

    0 vote(s)
  2. No, I have not.

  1. May 31, 2009 #1

    I would like to learn if you've ever heard of the positive charge atomic form-factor before my asking this question. The positive charge atomic form-factor fnn'(q) stands at the nucleus charge Z and describes the positive charge cloud in atoms for elastic scattering at large angles (n→n). It also describes inelastic scattering channels - hitting nucleus by a projectile excites an atom (n→n'). The elastic and inelastic positive charge atomic form-factors are entirely determined with atomic wave functions ψn(r) and they have nothing in common with the Hofstadter form-factor describing the proper nucleus size. The positive "cloud" size may be very big if the initial and the final atomic states ψn(r) are excited and metastable, like in Rydberg atoms. This is just effect of the nucleus motion around the atomic center of inertia. Physically it is of the same nature as the negative (electron) charge atomic form-factor Fnn'(q). The numerical difference is just in the "could" sizes - the negative one is larger (an), the positive is smaller ((me/Mp)an for Hydrogen, for example). Correspondingly the scattering angles where these form-factors work differ essentially - at small and large angles.

    The details can be found in my article "Atom as a "dressed" nucleus" in arXiv (http://arxiv.org/abs/0806.2635).

    Do not hesitate to leave your answer and thanks for participating in this poll.

    Last edited: Jun 1, 2009
  2. jcsd
  3. Jun 2, 2009 #2
    You can also leave your opinion on whether the effect of the positive charge smearing in atoms seems to you as realistic as the negative charge smearing or not. Of course, if you have not studied this subject (scattering from atoms, atomic form-factors), leave nothing.

    Last edited: Jun 3, 2009
  4. Jun 7, 2009 #3
    The positive charge cloud in Hydrogen is of the same shape as usual atomic orbitals but scaled down to much shorter distances. See figures for 2p and 3p states. Isn't it beautiful? I added a couple of other pictures.

    Attached Files:

    Last edited: Jun 8, 2009
  5. Jun 7, 2009 #4
    isnt that just the nuclear shells?
  6. Jun 8, 2009 #5
    The term "nuclear" is associated with the strong interactions. It is better to say "a nucleus shell in atom".

    Yes, the positive charge cloud is an atomic nucleus shell.

    Last edited: Jun 8, 2009
  7. Jun 9, 2009 #6
    Final remark (it is explained in details in "Atom...") concerning observation of these atomic nucleus shells. It is possible in the elastic scattering processes when the initial and the final states of the target atom is the same: ψn(r)→ψn(r). We have to deal with fast charged projectiles whose de Broglie wave-length is smaller than the cloud size. And we have to scatter them at large angles.
    In these conditions a fast charged projectile transfers a big momentum to the nucleus so the atom can get easily excited (inelastic processes: ψn(r)→ψn'(r)). In reality it is difficult, without special experimental facility, to distinguish the elastic from inelastic processes. When one observes only the scattered projectiles, all cross section (elastic and inelastic events) are added up experimentally. It is called the inclusive cross section. It is easy to show that the inclusive cross section dσinclusive=∑dσn→n' is reduced quite accurately to the Rutherford cross section, as if the target nucleus were "free" and situated at the atomic center of inertia. This fact explains why the notion of point-like particle finds the "experimental" support. In specially designed experiments one can distinguish the elastic dσn→n from inelastic cross sections and obtain the figures presented above.

    The journal version of "Atom..." is available at the Central European Journal of Physics site: http://www.springerlink.com/content/h3414375681x8635/?p=14dbc7f5eda74d6886686dc5b899036d&pi=0

    Last edited: Jun 9, 2009
  8. Jun 29, 2009 #7
    The poll ends up today.
    Last edited: Jun 30, 2009
  9. Jul 1, 2009 #8
    The poll had 870 visitors, they left 0 replies "Yes" and 5 replies "No", that is it.
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