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How did Meitner calculated the amount of energy lost...

  1. Oct 27, 2015 #1
    It's my first time here, so I'm not sure if this is the right place to post it. If I post it in the wrong section, then I'm sorry.

    Anyways, I just have a curious question. Based on this video I watched --> ""

    at around 1:40:42 , I really want to know how she actually calculated the amount of energy lost during the nuclear fission of the uranium atom by using E=mc^2. I'm just curious that's all because the video doesn't show the actual calculation. So, if one of you guys can show the process of the mathematics, that would be great!

    Thx!
     
  2. jcsd
  3. Oct 27, 2015 #2

    russ_watters

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    Staff: Mentor

  4. Oct 28, 2015 #3

    Borek

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    She says clearly that the two nuclei (produced in the fission) are lighter than the original nucleus of uranium by about 1/5 of the proton in mass. When you know this number it is just plug and chug
     
  5. Oct 28, 2015 #4

    russ_watters

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    Yeah - it was what she said right before that, before she calculated that result that I couldn't understand. Sounds like "let me do a packing friction calculation", but I don't think that's right....
     
  6. Oct 28, 2015 #5
    Yes, that's what she says.
    It seems to be sort of jargon of early nuclear physicists. :smile:
    See here, for example:
    https://en.wikipedia.org/wiki/Nuclear_binding_energy

    At the end of the section "measuring binding energy"
     
  7. Oct 28, 2015 #6

    OmCheeto

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    LISE MEITNER: "Wait, let me do a packing fraction calculation. The two nuclei are lighter than the original uranium nucleus by about one-fifth of a proton in mass".
    [ref: Nova transcript]

    I can't find the original letter that sparked the conversation, sent on 19 December, 1938, but I did find the paper published a few months later:

    Concerning the Existence of Alkaline Earth Metals Resulting from Neutron Irradiation of Uranium
    published 6 January 1939

    I'm afraid I can't follow it.

    Wiki gives a clue:
    I knew the theory behind mass defect, but not the history of its discovery.
    Very interesting.
    But how they determined the details, is still beyond me.
     
  8. Oct 28, 2015 #7

    OmCheeto

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    I plugged and chugged and came up with 169 mev, based on wiki's most convenient: U236 fission into Ba141 + Kr92 + 3 Neutrons image

    Specifics available upon request. :angel:

    ---------------------
    [edit]
    And given that I'm prone to forgetting where everything is:
    file: pf.random.homework.problems.numbers
    tab: fission of U236
     
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