Quote:
Originally posted by Jayjay
I'm going to do a google search on K/Ar and Ar/Ar right after posting this, but I wonder if there's an easy and short explanation what the problem with K/Ar is, and why Ar/Ar doesn't have this problem? I did some reading at talkorigins on these methods once, but I never did grok what the fundamental difference between the two was...
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Alright, I found a nice answer to this question
in here:
Quote:
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In the argon-argon method the rock is placed near the center of a nuclear reactor for a period of hours. A nuclear reactor emits a very large number of neutrons, which are capable of changing a small amount of the potassium-39 into argon-39. Argon-39 is not found in nature because it has only a 269-year half-life. (This half-life doesn't affect the argon-argon dating method as long as the measurements are made within about five years of the neutron dose). The rock is then heated in a furnace to release both the argon-40 and the argon-39 (representing the potassium) for analysis. The heating is done at incrementally higher temperatures and at each step the ratio of argon-40 to argon-39 is measured. If the argon-40 is from decay of potassium within the rock, it will come out at the same temperatures as the potassium-derived argon-39 and in a constant proportion. On the other hand, if there is some excess argon-40 in the rock it will cause a different ratio of argon-40 to argon-39 for some or many of the heating steps, so the different heating steps will not agree with each other.
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07-01-2003, 04:09 PM
