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Minimum wavelength of light and electrons? Microscope related.

  1. Feb 7, 2008 #1
    I noticed that websites usually say that the maximum effective magnification of a light microscope is 2000x, so electron microscopes are used for greater resolution due to their shorter wavelength, but don't photons in the gamma ray range have an even shorter wavelength, allowing them to see individual atoms?
     
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  3. Feb 7, 2008 #2

    mathman

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    Microscopes in general are designed on the basis of what is visible. Therefore the magnification is limited by the wavelength of light. Gamma rays cannot be seen by the human eye - you need to use appropriate detectors, not light microscopes.
     
  4. Feb 7, 2008 #3
    While the photons do have a smaller wavelength, they have a much greater energy, and this affects the measurement process greatly. Because they have such a large energy, they end up altering and possibly destroying the samples they look at. Once you get too large an energy, the photons will begin knocking off electrons (or if one were to try to use gamma rays, taking out whole nuclei) and stop giving you a good, focused image.
     
  5. Feb 7, 2008 #4

    Claude Bile

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    Also, no suitable optics exist to focus Gamma rays on to an image plane.

    Claude.
     
  6. Feb 7, 2008 #5
    At those high energeis, the gamma rays act more like particles then the waves we know and love.
     
  7. Feb 7, 2008 #6
    Is it possible a microscope like this could be created in the future though, for looking at things in more detail than an electron microscope albeit for a very short time before they became too damaged, perhaps even individual atoms?

    Also, do the electrons act as beta radiation and damage the cells themselves, I thought beta radiation was more ionising and damaging than gamma? Is gamma more or less damaging to the molecules than the electrons at the same wavelengths?
     
  8. Feb 7, 2008 #7

    gel

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    Surely its even worse for electrons than with photons. Simply combining [itex]p\lambda=h[/itex] and [itex]E^2=p^2c^2+m^2c^4[/itex] gives [itex]E=c\sqrt{h^2\lambda^{-2}+m^2c^2}[/itex]. So massless particles have the lowest energy for a given wavelength.

    Sounds likely to me. I've no idea how electron microscopes work, but I guess they must focus the electrons with an electromagnetic field, which isn't possible with light. Why don't lenses work with gamma rays?
     
  9. Feb 7, 2008 #8
    The lense has to be transparent to that frequency of light. For example, glass is quite transparent to visible light, while opaque to thermal IR. Silicon, on the other hand, is transparent to IR and opaque to visible light. Admittedly I do not know the transparencies of different materials to gamma radiation, but as it has such a high energy, as it passes through materials it is most likely going to interact and make a good number of elementary particles.

    As for looking at things briefly, you would need very many focused gamma rays, wihch would probably destroy your sample. It would be like trying to figure out the shape of an aluminium goose with a 22.

    Electron microscopes are a little more damaging at those wavelengths, yes, but they can be produced fairly easily. If you want to go smaller, you can turn to a scanning/tunnellig microscope for extremely detailed looks, easily finding details smaller then an atom. They have used EM waves to picture a single atom, but from what I remember the picture was a green dot a few pixels across on a black background.

    Now, if you want to get fairly technical, in Bose-Einstein Condensates, the many atoms there share one wave function, effectively making one atom in many places. We have pictured these with light, as well as many other techniques. In the process of taking the picture, we destroy the condensate, but it works.
     
  10. Feb 8, 2008 #9

    Andy Resnick

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    The rule of thumb for microscopy, any microscopy, is that the limit to magnification ("useful magnification") is about 1500 times the numerical aperture. Numerical aperture also sets the limit on the smallest resolvable detail.

    One way to increase the numerical aperture is to decrease the wavelength: UV microscopy, electron microscopy, etc. Aberration correction becomes difficult, but three has been some recent breakthroughs in correcting e-microscopy beams.

    Gamma rays are near impossible to refract; gamma-ray telescopes use grazing-angle incidence to focus the particles and look like gigantic mirrored tubes-at least the satellites do.

    Billiard balls have an even shorter deBroglie wavelength- but treating them as waves and focussing a billiard-ball microscope would be quite the engineering challenge. Never mind the damage done to any putative sample... care to volunteer? :)
     
  11. Feb 10, 2008 #10

    Claude Bile

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    Electron microscopes use magnetic lenses to focus and scan the beam.

    Claude.
     
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