Geochronology/Argon–argon dating

The age of a sample is given by the age equation:

$t={\frac {1}{\lambda }}\ln(J\times R+1)$

where λ is the radioactive decay constant of ⁴⁰K (approximately 5.5 x 10⁻¹⁰ year⁻¹, corresponding to a half-life of approximately 1.25 billion years), J is the J-factor (parameter associated with the irradiation process), and R is the ⁴⁰Ar*/³⁹Ar ratio. The J factor relates to the fluence of the neutron bombardment during the irradiation process; a denser flow of neutron particles will convert more atoms of ³⁹K to ³⁹Ar than a less dense one.

One problem with argon-argon dating has been a slight discrepancy with other methods of dating. A correction of 0.65% is needed.

See also

• Potassium–argon dating
• Radiocarbon dating
• Uranium–lead dating
• Uranium-thorium dating

External links

• WiscAr Geochronology Laboratory, University of Wisconsin-Madison
• UC Berkeley press release: "Precise dating of the destruction of Pompeii proves argon-argon method can reliably date rocks as young as 2,000 years"
• Argon Isotope Facility of the Scottish Universities Environmental Research Council
• Open University Ar/Ar and Noble Gas Laboratory
• Argon Laboratory / Australian National University

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