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Methods for determination of structure of solid?

  1. Dec 10, 2009 #1
    Hi, just a basic question , what are the main methods of determining the structure of a solid in order to test its genuinety i.e. gold....
    if i were to be given a piece of gold, how would i check that it is genuine gold?

    could i use x ray diffraction (If so what measurements /tests would i need to take), line spectra technique etc????
    and what destructive methods could i use to figure this out?

    thanks!
     
  2. jcsd
  3. Dec 10, 2009 #2

    alxm

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    I suppose X-ray diffraction could be used, but it wouldn't be the easiest way. (being that the information gained is more related to the geometric structure than the electronic structure)

    But certainly X-rays. XRF, X-ray fluorescence would be my choice. It'd be destructive if you did it on, say, an organic molecule, but not on a lump of metal. Bombard the sucker and look for the characteristic lines of the different elements, basically.
     
  4. Dec 10, 2009 #3
    Tests that use surface tests are not sufficient to differentiate between gold and gold-plated tungsten. Density is a good test but does not rule out tungsten.

    X-ray fluorescence is better, but still the x-ray penetration is shallow. The conductivity of gold is much better than tungsten, but because of eddy currents, the test frequency would have to be very low. If you put a gold bar in a solenoid and measure the complex impedance (both inductance and resistive losses) vs frequency, this would be a valid signature (tungsten has twice the bulk resistivity of gold) and can be done quickly (The real and imaginary components of the solenoid impedance are related by the Kramers Kronig relations). I have measured the quality of big (including superconducting) magnets this way down to 5 Hz.

    Put a neutron source near gold and activate it to Au-198, which has a 2.7 day half life, and detect the gammas. Neutrons have a very good penetration, and a decay gamma has a 1088 KeV energy (about the best energy for escaping from gold).

    Drill a hole through it, or melt it.

    [added] One source on the web proposes using large neodymium magnets to make an eddy current test conceptually similar to sliding a neodymium magnet down a copper tube. This would probably require several (2? 4?) large neodymium magnets in a steel frame. The gold would resist sliding through the magnets about 2x more than the tungsten would, but not quite as much as copper or silver.

    Bob S
     
    Last edited: Dec 10, 2009
  5. Dec 23, 2009 #4
    Depth profile with secondary ions mass spectrometry.

    regards
    RJ
     
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