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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.

  2. jcsd
  3. Nov 22, 2005 #2


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    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 [Broken]
    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 [Broken]
    Pb 202 - - 52500 yr (probably as close to 48000 as one will get)

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

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

    http://wwwndc.tokai.jaeri.go.jp/CN04/ [Broken]

    Perhaps one could try a linear combination of one or two which would appoximate a radionuclide with half life of 48,000 years.
    Last edited by a moderator: May 2, 2017
  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


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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


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    Dearly Missed

    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
    Last edited: Nov 25, 2005
  8. Nov 25, 2005 #7


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    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]


    has a half-life of nearly 1.3 BILLION YEARS.

    Dr. Gregory Greenman
    Last edited by a moderator: Apr 21, 2017
  9. Dec 24, 2005 #8
    As shown below from the web link, the decay of Rb-87 to Sr-87 has a 1/2 life of 48,800 years--this should work well for your needs of 48,000 y. http://www.chemsoc.org/chembytes/ezine/2002/corfield_jan02.htm [Broken]
    System Material Half-life/years Age range/years
    Rb-87-Sr-87 Minerals (eg mica) 48,800m 60-4500m
    And, this site:
    indicates that one can measure to age of exactly 48,000 years using ratio of C14 / C12.
    Last edited by a moderator: May 2, 2017
  10. Dec 25, 2005 #9


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

    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.
    Last edited by a moderator: May 2, 2017
  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.
    Last edited by a moderator: May 2, 2017
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