Krypton is a noble gas with eight isotopes, 6 stable and 2 radioactive. The stable isotopes are considered separately with the noble gases. Natural variation in the abundance of these isotopes can be useful in determining paleo recharge temperatures of groundwater. ⁸⁵Kr is a cosmogenic nuclide that is produced in the atmosphere and through nuclear fuel processing. It has a short half-life and can be used to date recent groundwater recharge.

• Cost of Analysis
  
• Origin
  
• Measurement Techniques
  
• Hydrological Applications
  
• Other applications
• References and Further Reading
• Internet Resources

Cost of Analysis (return to top)

No laboratories currently offer ⁸⁵Kr analysis as a standard procedure.




Origin (return to top)

Natural
⁸⁵Kr is created naturally in the atmosphere when cosmic rays hit ⁸⁵Kr. ⁸⁵Kr reaches the earth's surface through precipitation (as a solute in the rain). This natural cosmogenic production of ⁸⁵Kr is extremely small.

⁸⁵Kr is also created naturally through the spontaneous, neutron-induced fission of uranium and thorium in the earth's crust. This production accounts for an even smaller percentage of the amount of ⁸⁵Kr on earth.

Anthropogenic
Atmospheric nuclear testing during the 1940's through 1963 contributed to a significant increase in the level of atmospheric ⁸⁵Kr. But the majority of ⁸⁵Kr in the atmosphere and on the earth's surface is a result of nuclear fuel reprocessing, beginning in the 1940's. ⁸⁵Kr is an abundant fission product of uranium and plutonium and is released into the atmosphere during stages of nuclear fuel handling. Because of this, the ⁸⁵Kr activity in the atmosphere has continuously increased since the 1950's.

Measurement Techniques (return to top)

Counting Rate
⁸⁵Kr can be measured by through decay counting techniques. The water sample must be degassed, the Kr separated and concentrated for analysis. Given the low concentration of ⁸⁵Kr, a few hundred liters of groundwater are needed for analysis and counting times of ~1 week are required for each sample.


Hydrological Applications (return to top)

⁸⁵Kr can be used to date young groundwater. Due to the fast decay rate and minimal natural production in the earth, the absence of ⁸⁵Kr verifies that groundwater is older than 1950.

If ⁸⁵Kr is combined with an additional radioactive isotope with a similar half-life (such as ³H), one can gain additional confidence in results. Under the correct hydrologic conditions (as in aquifers that have high permeablility or shallow circulation), isotopes can be used in combination to trace groundwater flow paths and verify flow models.

The main disadvantages in using ⁸⁵Kr are large sample size requirements and high costs due to the specialized measurement methods. Its short half-life and increasing concentrations in the atmosphere make ⁸⁵Kr a potential replacement for ³H as tritium levels continue to decline.

(See paper by Torsten Lange (University of Freiberg) for more information on the hydrological uses of ⁸⁵Kr)

Other applications (return to top)

⁸⁵Kr can trace the effect atomic facilities have on the surrounding environment.

References and further reading (return to top)

• Cook, P.G., and D.K. Solomon, Recent advances in dating young groundwater: chlorofluorocarbons, ³H/³He, and ⁸⁵Kr, J. of Hydrology, 191: 245-265, 1996.



• Ekwurzel, B., P. Schlosser, W.M. Smethie Jr., L.N. Palmer, E. Busenberg, R.L. Michel, Dating of shallow groundwater: comparison of the transient tracers ³H/³He, Chlorofluorocarbons, and ⁸⁵Kr, Water Resour. Res., 30(6): 1693-1708, 1994.



• Florkowski, T., and K. Rozanski, Radioactive noble gases in the terrestrial environment, in Handbook of environmental isotope geochemistry, ed. by P. Fritz and J.Ch. Fontes, Elsevier, Amsterdam, 1986.



• Forster, M., H.H. Loosli, and S. Weise, ³⁹Ar, ⁸⁵Kr, ³He^- and ³H isotope dating of ground water in the Bocholt and Segeberger Forst aquifer systems, in Progress in Hydrogeochemistry, ed. by G. Malthess, F. H. Frimmel, H. D. Schulz, and E. Uschowski, pp. 467-475, Springer-Verlag, Berlin, 1992.



• Lehmann, B., H. H. Loosli, D. Rauber, N. Thonnard, and D. Willis, ⁸¹Kr and ⁸⁵Kr in groundwater, milk river aquifer, Alberta, Canada, Applied Geochem. 6: 419-423, 1991.



• Loosli, H.H., Lehmann, B.E., and W.M. Smethie, Noble gas radioisotopes, in Environmental Tracers in Subsurface Hydrology, ed. by P.G. Cook and A.L. Herczeg, Klewer, Boston, 2000.



• Ludin, A.I., and B.E. Lehmann, High-resolution diode-laser spectroscopy on a fast beam of metastable atoms for detecting very rare krypton isotopes, Applied Physics, B, 61: 461-465, 1995.



• Weiss, W., H. Sartorius, and H. Stockburge, H., Global distribution of atmospheric ⁸⁵Kr, in Isotopes of Noble Gases as Tracers in Environmental Studies, IAEA, Vienna, pp. 29-62, 1992.

Internet resources (return to top)

Mook, W.G., and J.J. de Vries, Environmental Isotopes in the Hydrological Cycle: Principles and Applications, vol. 1: Introduction - Theory, Methods, Review, 2001.

Lawrence Berkeley National Laboratory, Nuclear Science Division, Berkeley Laboratory Isotopes Project, Isotopes of Krypton.

Lange, Torsten, Investigations on water regimes and transport processes of substances in waste and mining dumps and natural aquifers by environmental isotopes - applying ⁸⁵Kr as an alternative isotope in hydrogeology.

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