# Geochronology/Argon–argon dating

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

where λ is the radioactive decay constant of ^{40}K (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 ^{40}Ar*/^{39}Ar 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 ^{39}K to ^{39}Ar than a less dense one.

One problem with argon-argon dating has been a slight discrepancy with other methods of dating.^{[1]} A correction of 0.65% is needed.^{[2]}

## See also

edit## References

edit- ↑ Renne, P. R. (1998). "Absolute Ages Aren't Exactly".
*Science***282**(5395): 1840–1841. doi:10.1126/science.282.5395.1840. - ↑ Kuiper, K. F.; Deino, A.; Hilgen, F. J.; Krijgsman, W.; Renne, P. R.; Wijbrans, J. R. (2008). "Synchronizing Rock Clocks of Earth History".
*Science***320**(5875): 500–504. doi:10.1126/science.1154339.

## External links

edit- 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