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Re: Radiocarbon Dating



Brandon, etc.:

    The method that I remember (besides thermoluminescence), is the
measurement of the ratio of the radioactive material to its decay elements.
For example, Uranium (U-235 or U-238) runs into the Thorium series then
breakdowns into Radium and Radon, and finally, into Lead (the stable
isotope).

    If you find U-235 in your volcanic tuft, and you also find (stable) Lead
associated directly with it, you can work out how old the deposit is, by
comparing the amount of U-235 with the amount of Lead.  If the sample is 75%
U-235 and 15% Lead (and 10% other), then you know that the sample is
approximately 300 mya.  (This is a very rough and very crude estimate - done
off the top of my head).  About half of the half of the original amount (1/2
* 1/2 = 1/4) of U-235 has decayed into other materials - meaning that only
half of its half life has passed - therefore: ~300 mya.

    Josh Smith could probably give you more detailed and (more) correct
information, if he happens to be checking the list.  If I could find one of
my documents (which I seem to have buried somewhere), I could be slightly
more precise myself.  :-)

        Allan Edels

-----Original Message-----
From: Haist, Brandon <brandonc@advant.com>
To: dinosaur@usc.edu <dinosaur@usc.edu>
Date: Saturday, December 05, 1998 7:41 PM
Subject: Re: Radiocarbon Dating


>Yes, the before mentioned bood "The Handy Science Answer Book" says the use
>of elements are:
>
>Uranium-238 ~half life=4.5 billion years
>
>Uranium-235 ~half life=704 million years
>
>Thorium-232 ~half life=14 billion years
>
>Rubidium-87 ~half life=48.8 billion years
>
>Potassium-40 ~half life=1.25 billion years
>
>Samarium-147 ~half life=106 billion years
>
>These are said to be used in dating techniques of gas formation light
>emission (called thermoluminescence).
>
>What are some other forms of dating?
>~Brandon Haist
>
>
>