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)

how old

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

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)

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)

Thanks, it does help. I wish that the text would mention that and would write out the equation. I guessed that there was proton emission taking place but it is nice to have it in text. Also, more discussion about the nuclear physics would be nice. Does 39 K capture a neutron and turn to 40 K? Does 40 Ar capture a neutron and turn into 41 Ar. Vmelkon (talk) 23:53, 22 December 2014 (UTC)

The reaction is 39K(n,p)39Ar, an example of an (n-p) reaction. --Kent G. Budge (talk) 22:03, 8 October 2020 (UTC)

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)

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

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. — Preceding unsigned comment added by Joelgombiner (talk • contribs) 02:16, 17 October 2013

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Lack of references

There are four references given for this Wiki page; however none are included in the intro section where a number of claims are made (most accurate ...), none present in the methods section, and none present in the 'age equation' section. Astrophysicalchemist (talk) 14:57, 19 February 2023 (UTC)