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Radioactive isotope with a half-life of 48,000 years

  1. Nov 21, 2005 #1
    Is it possible to identify such an isotope? What are my choices if I wanted such a long half-life product. (Ultimately, I need it to activate a timing switch....!) :smile:

    Thanks, anyone for any pointers.

    AA
     
  2. jcsd
  3. Nov 22, 2005 #2

    Astronuc

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    Staff: Mentor

    Doesn't appear to be a radionuclide with a half-life of 48,000 years, but some are close.

    Try these - look at nuclides with green color

    http://wwwndc.tokai.jaeri.go.jp/CN04/CN024.html
    Nuclide Half-life (years)
    Pa-231 - - 32800 yr
    Th-230 - - 75400
    Pu-239 - - 24100 (forget it)

    http://wwwndc.tokai.jaeri.go.jp/CN04/CN021.html
    Pb 202 - - 52500 yr (probably as close to 48000 as one will get)

    http://wwwndc.tokai.jaeri.go.jp/CN04/CN009.html
    Nb- 94 - - 20300 yr

    http://wwwndc.tokai.jaeri.go.jp/CN04/CN005.html
    Ni- 59 - - 76000 yr

    http://wwwndc.tokai.jaeri.go.jp/CN04/

    Perhaps one could try a linear combination of one or two which would appoximate a radionuclide with half life of 48,000 years.
     
  4. Nov 24, 2005 #3
    I'll take the Plutonium 239 and use its 'quarter-life', i.e. when 75% of the original mass has been depleted through radioactive emissions, the timing switch will be triggered... exactly 48,200 years later. :wink:
     
  5. Nov 24, 2005 #4

    enigma

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    I don't know if you are being serious or not, AA Institute.

    Do take note of what Plutonium 239 is typically used for.
     
  6. Nov 25, 2005 #5
    I know what you're thinking.... No, it won't be like 'Silent Running' where the guy blew himself to kingdom come - :rofl:

    No, in my case, the Pu-239 is going to trigger a revival sequence for crew in hibernation <cut - don't want to give the story away!> :smile:
     
  7. Nov 25, 2005 #6

    Morbius

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    AA Institute,
    "Silent Running" - one of the WORST sci-fi movies - EVER!!!

    There's the part where the first cargo ship launches one of the forest
    capsules into space with its nuclear self-destruct bomb - KABOOM!!!
    Bruce Dern hears the explosion - and can't stand the sound of his
    beloved forests being destroyed.

    Did any of the idiots that made that film realize that sound doesn't
    travel in space due to the lack of a medium [air] to carry the sound waves?

    Dr. Gregory Greenman
    Physicist
     
    Last edited: Nov 25, 2005
  8. Nov 25, 2005 #7

    Morbius

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    AA,

    If you're asking if it's possible to identify isotopes with half-lives or
    48,000 years OR LONGER - the answer to that is YES.

    For example, Potassium-40 [K-40]

    http://sutekh.nd.rl.ac.uk/cgi-bin/CoNquery?nuc=K40

    has a half-life of nearly 1.3 BILLION YEARS.

    Dr. Gregory Greenman
    Physicist
     
  9. Dec 24, 2005 #8
  10. Dec 25, 2005 #9

    Astronuc

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    Staff: Mentor

    Regarding Rb-87, one has to read the data carefully at - http://www.chemsoc.org/chembytes/ezine/2002/corfield_jan02.htm.

    The half-life is given as 48,000m years (this can be misleading), where m = million, i.e. the half-life is 48 billion years, which for a radionuclide is more or less stable.

    The other concern is how to determine at sometime in the future, e.g. the precise time, i.e. 48,000 years. The activity at 48,000 years is 'very close' to the activity at 47,500 or 48,500 years. The question is - how precise does one have to be?

    One could use several isotopes of different, but similarly long half-lives, and perhaps look at the activity ratios.

    The longer the half-life, the less precise the measurement of time.
     
  11. Dec 26, 2005 #10
    Yes, thank you--my error--I missed the "m". I think the OP is left only with "ratios" of isotopes to get to 48,000 y 1/2 life for dating.
     
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