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Cosmogenic Isotope Studies - Scientific Technique

Cosmogenic Isotope Dating at BAS

Cosmogenic isotopes (e.g. Beryllium-10 and Aluminium-26) are created when elements in the atmosphere or earth are bombarded by cosmic rays that penetrate the atmosphere from outer space. The accumulation of these isotopes within a rock surface can be used to establish how long it has been exposed to cosmic radiation, rather than being shielded by ice or sediment. Exposures of surfaces from between a few thousand to about 10 million years old can be dated by the measurement of the Be-10 and Al-26 isotopes. More detailed information is given in Gosse and Phillips (2001) and Bierman et al. (1999).

The cosmogenic preparation laboratory at BAS

As a rock surface is bombarded by cosmic rays, Be-10 and Al-26 are created in the quartz crystals. A laboratory has been set up at the British Antarctic Survey headquarters in Cambridge to prepare samples of pure quartz for cosmogenic isotope analysis. The rocks collected from the field area are crushed and a quartz rich fraction is physically separated from the rest of the minerals using the low density of quartz compared to the other things in the rock. This fraction is then cleaned in the lab to remove another low density mineral called feldspar. The pure quartz can then be chemically treated to collect the Be-10 and Al-26 for analysis on an Accelerator Mass Spectrometer. NERC has one of these machines at the Scottish Universities Environmental Research Centre in East Kilbride, near Glasgow. Contact Dr. Joanne Johnson or Dr. Morag Hunter for further information.

References

Bierman, P.R., Marsella, K.A., Patterson, C., Davis, P.T., and Caffee, M., 1999. Mid-Pleistocene cosmogenic minimum-age limits for pre-Wisconsinan glacial surfaces in southwestern Minnestoa and southern Baffin Island: a multiple nuclide approach. Geomorphology, v. 27, p.25-39.

Gosse, J.C. and Phillips, F.M., 2001. Terrestrial in situ cosmogenic nuclides: theory and application. Quaternary Science Reviews, 20(14): 1475-1560.