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How scientists test assumptions.

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  • JonF
    replied
    Actually, radon is part of the system. It's an intermediate in the decay chains of 238U, 232Th, and 235U.

    We can describe the "evolution" of a decay chain system over time by a set of coupled differential equations, one for each isotope in the chain. Each equation includes the rate of production of the isotope from decay of its parent (if there is one) which depends on the amount of its parent, and includes the rate of destruction of the isotope (if it's not stable) which depends on the amount of that isotope. This is pretty messy, but fortuitously in the three systems named above the half-life of the top of the chain is much longer than the half-life of the longest-lived intermediate. In those cases the system approaches "secular equilibrium" asymptotically. (After 5-20 half-lives of the longest lived intermediate you might as well say it's gotten there.) In secular equilibrium the production rate of each intermediate is exactly equal to its destruction rate and exactly equal to the destruction rate of the top isotope in the chain and exactly equal to the production rate of the final stable isotope.

    Therefore, for each atom of the top isotope that is destroyed one atom of the final stable isotope is produced. This is exactly the same as if the top isotope decayed directly to the final isotope except the produced atom is not the same atom as the destroyed atom. We don't care about labeling individual atoms in the math, so we can ignore all the differential equations and treat any system old enough to be in secular equilibrium as a simple A decays to B system. (There are methods for younger systems that measure the distance from secular equilibrium.)

    But if there is another significant term in any of the equations, e.g. a leakage term, all bets are off. I don't know off hand what quantitative effect it would have but there would be one. Without looking I presume there is good reason for Valley et al to ignore this possibility.
    Last edited by JonF; 03-02-2014, 07:47 AM.

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  • rwatts
    replied
    Originally posted by 37818 View Post
    Thanks.

    Note this reference too: http://www.minsocam.org/ammin/AM40/AM40_481.pdf
    Thanks for the reference, although as shuny writes, it's perhaps somewhat irrelevant here because radon gas is not part of the dating system. I did note this paragraph however (emphasis mine):-

    "The radon leakage of the Contact Lake specimenis high even at room temperature. By analogy with other similar specimens, taking into account the average temperature estimated at 150oC., the actual integrated leakage should approach 15/6 which would bring the 206/238 and 207 /206 ages into line with the 207/235. This suggests that leaching of uranium or lead has been negligible. "

    I'm not sure, whether or not it is this you were wishing to bring to my attention.

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  • shunyadragon
    replied
    Originally posted by 37818 View Post
    Thanks.

    Note this reference too: http://www.minsocam.org/ammin/AM40/AM40_481.pdf
    I do not believe this applies to case of zircons.

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  • 37818
    replied
    Originally posted by rwatts View Post
    The paper behind this article looks as if it would be a fascinating read (including a long slog of looking up and trying to understand definitions):-

    http://www.livescience.com/43584-ear...ls-zircon.html

    In essence, it seems as if, using new technology, geologists have been able to track the distribution of daughter lead (due to radio active decay) in a zircon, thereby firming up the idea that it does not necessarily leak out of the containing crystal. Evidence has been that zirons are closed systems. These geologists counted atoms to demonstrate this to be the case in a few of the crystals at least.

    Thanks to poster mountaineer_elf from another forum.
    Thanks.

    Note this reference too: http://www.minsocam.org/ammin/AM40/AM40_481.pdf

    Leave a comment:


  • LostSheep
    replied
    Very cool article!

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  • shunyadragon
    replied
    Nice reference!!

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  • rwatts
    started a topic How scientists test assumptions.

    How scientists test assumptions.

    The paper behind this article looks as if it would be a fascinating read (including a long slog of looking up and trying to understand definitions):-

    http://www.livescience.com/43584-ear...ls-zircon.html

    In essence, it seems as if, using new technology, geologists have been able to track the distribution of daughter lead (due to radio active decay) in a zircon, thereby firming up the idea that it does not necessarily leak out of the containing crystal. Evidence has been that zirons are closed systems. These geologists counted atoms to demonstrate this to be the case in a few of the crystals at least.

    Thanks to poster mountaineer_elf from another forum.
    Last edited by rwatts; 02-25-2014, 01:32 PM.

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