Talk:Argon–argon dating

Precision vs. Accuracy in opening sentence

The opening sentence makes the claim that Ar/Ar offers greater accuracy than K/Ar. Precision is likely greater, but since absolute ages (accuracy) depend on the monitor standards, accuracy falls by the wayside. I'm curious to hear other thoughts on this.

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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)[reply]

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

how old

In geology, how old would the rock or lava be in argon-argon dating? Black Tusk 13:21, 8 September 2007 (UTC)[reply]

Hey guys, I noticed the 'relative dating only' section is pretty limited and contains some inaccuracies. I'm making some small adjustments to bring it up to standard. — Preceding unsigned comment added by Knijneburg (talk • contribs) 09:11, 20 August 2013 (UTC)[reply]

39-Ar production by neutron irradiation from 39-K

A recent edit suggested that it is 40K, not 39K, that is changed to 39Ar during irradiation prior to Ar/Ar analysis for dating. This is incorrect, and the original version has been reinstated.

The terrestrial 39K/40K is constant for any given point in time, therefore knowledge of the 39K/40Ar can also give the 40K/40Ar. During Ar-Ar dating, 39K is converted to 39Ar by irradiation with fast neutrons in a neutron capture, proton emission reaction. I hope this helps. Rickert (talk) 11:40, 5 January 2008 (UTC)[reply]

possible update

There was a recent update on argon-argon dating that slightly changes the dating (by 0.1%). I would like to add that, but I am also utterly new to this. So I would like to give warning of intent, and give everyone a chance to brace themselves before I jump in. Or even to warn me off, or offer sage advice. :-) J. Johnson (talk) 00:27, 26 November 2008 (UTC)[reply]

Done. J. Johnson (talk) 22:41, 1 December 2008 (UTC)[reply]