Talk:Argon-argon dating

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Which radiation is used to produce ³⁹Ar from ³⁹K ? The original ³⁹K/⁴⁰K ratio of the sample has to be known in advance, else you have to do Potassium-Argon dating. 193.171.121.30 14:00, 16 December 2005 (UTC)

I believe it is gamma radiation; and you do not have to know the ³⁹K/⁴⁰K ratio in advance, as you can do a correction for it with the internal Ar ratios of the sample, and a correction for Chlorine-37, etc, etc. You also need a flux monitor to calculate the radiation flux (or J-constant) of the reactor which describes the efficiency of the irradiation. Generally this is a crystal of the Bishops Tuff or other natural, well-dated mineral.

Rolinator 09:25, 21 December 2005 (UTC)

Thanks for the answer, but I still don't see how you get the age without knowing the ⁴⁰K/³⁹K ratio. The ⁴⁰Ar concentration should be

c_Ar-40 = c_{K-40,original} * (1 - exp(-t/τ))

or expressed in terms of the current potassium content:

c_Ar-40 = c_K-40 * (exp(t/τ) - 1)

OTOH we have

c_Ar-39 = J*c_K-39

There are only 2 equations but the 3 unknowns c_K-39, c_K-40 and t. What am I missing about the internal Ar ratios?

Concerning the kind of radiation, I think it should rather be beta radiation because ³⁹Ar decays to ³⁹K by emitting a beta particle (you need a negative charge for the transmutation, and I have never heard about gamma radiation inducing electron capture). 193.171.121.30 12:41, 21 December 2005 (UTC)

This press release states that it is actually the conversion ⁴⁰K -> ³⁹Ar by neutron irradiation. Then of course there is no need to know anything about ³⁹K. 193.171.121.30 02:03, 20 January 2006 (UTC)

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Hi all. I removed an erroneous/misleading statement in the opening paragraph. I will hopefully soon find time to put something proper in it's place rather than just deleting things and leaving the butchered article. Cheers Rickert 19:07, 3 February 2006 (UTC)

Corrected my butchering. Still a long way to go.Rickert 23:08, 13 March 2006 (UTC)