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Precision measurements of atomic mass.

  1. Apr 11, 2015 #1
    Hello

    I have been trying to find out how the data for the atomic mass of different isotopes is processed. I am vaguely familiar with mass spectrometry and other techniques used for the measurements and I know that the experimental results are coordinated by the Atomic Mass Data Centre.

    I am particularly interested in atomic hydrogen but how is the data processed? What measurements are needed and how is the data processed to calculate the mass of hydrogen in, for example, its ground state. I think I know the answer but I would like confirmation.

    I have a rather large paper on the subject of mass measurement coordination but I find it a very heavy read and I think it assumes a lot of prior metrological knowledge on the part of the reader.

    Thank you.
     
  2. jcsd
  3. Apr 11, 2015 #2

    Simon Bridge

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    The data is "processed" by someone looking at it and making notes on paper ... but I suspect that is not what you are after.
    The output of a mass spectrometer is usually a wiggly line on a printout or a screen.

    Perhaps you want to know how putting ions through a magnetic field ends up as a wiggly line on a screen?
    In which case it would help if you described as much of the process as you have figured out so far and we can correct misconceptions, fill in any important gaps, and finish it off for you.
     
  4. Apr 11, 2015 #3
    Thank you for your reply,
    I'm roughly familiar with with the principle of mass spectrometry and other experimental techniques used but what I want to know is how the results are coordinated. The Atomic Mass Data Centre receive results from a large number of experiments and these are processed by the centre so as to calculate mass data of the type which is published by organisations such as NPL and NIST.
    I want to know how the atomic mass of hydrogen is calculated. What raw data for masses is needed and how is this data converted to calculate the mass of the neutral hydrogen atom? I'm fairly confident I know (knew) the answer, and I think it's simple but when I tried to confirm it using, what I assume to be the latest and most precise data available the numbers were close but didn't match, even within the limits of uncertainty.
     
  5. Apr 11, 2015 #4

    Simon Bridge

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    Oh you want to know how the results from a large number of experiments turns into the official number?
    A commitee works out which results to use and how to handle them. Usually there is a standard measurement method that gets decided on.
    This is the same for all weights and measures.

    If that is not it then perhaps you should show us what you did that did not turn out as you hoped?
     
  6. Apr 12, 2015 #5
    Thank you again Simon,
    I tried the numbers again but this time with the aid of the Nist programme that converted between different energy units. I think I miscalculated the conversions first time round. This time there was the match I expected.
     
  7. Apr 13, 2015 #6

    Simon Bridge

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    Oh well that would do it - well done :)
     
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