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Where can I get C14 data for cellulosic material?

  1. Mar 2, 2009 #1
    The cosmic radiation that creates C14 from nitrogen which then converts into radiated CO2 and is absorbed into plants during photosynthesis can be used for Carbon 14 dating but the data relating to the concentration in plants is hard to find. If a company is claiming to make renewable fuel from cellulosic material, the carbon in the fuel should have the same isotopic ratio as the feedstock. Does anyone know of feedstock tests others have done?

    Also can anyone comment about the radioactive carbon in cellulosic material and how it may react different from the normal carbon 12? Are Carbon 14 bonds stronger than Carbon 12?
     
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  3. Mar 2, 2009 #2

    mgb_phys

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    The concentration in plants will be (almost) exactly the same concentration as in th eair - that's how the whole C14 dating works, while the plant it alive the ratio is in equilibrium with air.
    The bond strengths should be very similair, there is very little chemical difference between isotopes (in gases there is a slight difference form the differing density).

    Why does this matter for a biofuel application?
     
  4. Mar 3, 2009 #3
    I am just wondering if the radio isotopic carbon might be more likely to become an uncompressed gas or a biofuel liquid during the pyrolysis process.
     
  5. Mar 3, 2009 #4

    Chronos

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    Provide reference to papers asserting C14 exists in space. I challenge this claim. It would be a remarkable discovery if true.
     
  6. Mar 3, 2009 #5

    Chalnoth

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    No. There are no chemical differences between C12 and C14. The only small differences are as a result of the different masses, which means that in order to differentiate between the two we use mass spectrometry, which is a method of separating out atoms of different masses to very high accuracy.

    Basically you first ionize the atoms, send 'em through a magnetic field, and the more massive the atom, the less it is deflected, so the different isotopes come out at different places on the detection apparatus on the other side of the magnet.
     
  7. Mar 3, 2009 #6
    I found the below graph at wikipedia:
    600px-Radiocarbon_bomb_spike.svg.png
    Now I need to figure how to convert pMC/percent to a moles % or anything I can comprehend.
     
  8. Mar 3, 2009 #7

    Chalnoth

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    The problem is that graph is scaled to the natural level, so you'd have to know the natural level of C14 in the atmosphere (the excess was caused by nuclear testing).
     
  9. Mar 4, 2009 #8

    mgb_phys

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    C14 is (according to wiki) about 1 ppt of C12, or 600billion atoms/mole of carbon.
    The accurate ratio is hard to find because most standards work in terms of decay rate rather than proportion.
    Be careful - most of the Carbon-Dating sites thrown up by google are young earth creationists or others trying to disprove carbon dating.
     
  10. Mar 4, 2009 #9

    Vanadium 50

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    Really? I'd imagine that they used a mass spec rather than trying to count decays. I get a count rate of 0.2 Bq/g for (modern) carbon, which is very small, and very hard to measure.
     
  11. Mar 4, 2009 #10

    mgb_phys

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    Everyone use MS/AMS now, but it seems that they all still think in terms of Bq/g - even if the instrument is really counting atoms it is calibrated in terms of decay rate.
     
  12. Jun 1, 2009 #11
    So since mass of the elements somewhat affects the bond strength how might the reactions differ?

    Would you say that if there is a reaction with a different limiting reactant, the weaker bonds would be broken before the stronger ones and depending on the amount of the other limiting reactant, the stronger bonded elements may not get used in a reaction?
     
  13. Jun 1, 2009 #12

    Chalnoth

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    As the gravitational force is more than 10^-40 times weaker than the electromagnetic force, its effects on bond strengths can be safely neglected for all practical purposes.
     
  14. Jun 1, 2009 #13
    How about if the system is in a vacuum - would there be zero gravity and the gravitational forces canceled out?
     
  15. Jun 1, 2009 #14

    Chalnoth

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    The external gravitational field has some small effect upon the behavior of large structures (which in molecular terms would be things like cells: we're still talking tiny here), as well as a statistical effect on the overall distribution of the various isotopes. But it hardly has any impact on chemical bonds.
     
  16. Jun 3, 2009 #15
    In which ways may these isotopes be separated?
     
  17. Jun 3, 2009 #16

    Chalnoth

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    The way they're typically separated to day is through the following process:

    1. Strip the electrons from the atoms.
    2. Send the nuclei through a magnetic field. The paths of the nuclei will deflect by an amount dependent upon their mass. Count the amount that deflect by amount X verses those that deflect by amount Y to get a measurement of the ratio between the two.

    This is but one method, by the way. People have come up with a large number of similar techniques for mass spectrometry. You can read up more on the subject here:
    http://en.wikipedia.org/wiki/Mass_spectrometry
     
  18. Jul 7, 2009 #17
    How do you determine the difference of bond strengths between C12-C12 and C12-C14?
     
  19. Jul 7, 2009 #18

    Chalnoth

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    Well, an easy way would be to just sit down and calculate it: the electromagnetic interaction for C12-C12 is identical to the one for C12-C14. Only the gravitational interaction is different. So we'd be talking a difference roughly around one part in 1040 times the bond strength of C12-C12.

    But if you wanted to actually measure it experimentally, well, an easy way would be to prepare two gases with different amounts of each isotope, and examine their bond strengths separately. I don't think you could measure the difference in this case, as I'm not aware of any experiment that is sensitive to one part in 1040.
     
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