What are 10Be, 9Be and 7Be?

10Be and 7Be are radioactive isotopes of beryllium that are produced in the Earth’s atmosphere and surface, through reactions induced by highly energetic cosmic rays. The radiometric half-lives of these cosmogenic isotopes are 1.36 million years (10Be) and 53.3 days (7Be), which makes them useful, especially 10Be, to various branches of the geosciences.

Detectable amounts of 10Be and 7Be exist in rainwater, snow, and surface water. Whereas 7Be is too short-lived to accumulate in the large reservoirs of the ocean and ocean floors, 10Be is found also in shallow and deep ocean sediments. 9Be, the only stable isotope of beryllium, is sourced from erosion of continental rock material and land surfaces.

Beryllium isotope profiles in an Antarctic soil from the Taylor Valley. Graham, I.J., Ditchburn, R.G., Claridge, G.C.G., Whitehead, N.E., Zondervan, A. & Sheppard, D.S., 2002. Dating Antarctic soils using atmosphere-derived 10Be and nitrate. Royal Society of NZ Bulletin 35: 429-436 (proceedings of 8th International Symposium on Antarctic Earth Sciences, Wellington).

Beryllium isotope profiles in an Antarctic soil from the Taylor Valley. Graham, I.J., Ditchburn, R.G., Claridge, G.C.G., Whitehead, N.E., Zondervan, A. & Sheppard, D.S., 2002. Dating Antarctic soils using atmosphere-derived 10Be and nitrate. Royal Society of NZ Bulletin 35: 429-436 (proceedings of 8th International Symposium on Antarctic Earth Sciences, Wellington).

The isotope abundance ratio, i.e. 10Be/9Be (atom/atom) is used for dating ferromanganese nodules and manganese crusts on ocean floors (growth rates are determined from the ages), and to estimate sedimentation rates during the past c. 15 Ma. 10Be has also been used in the study of other processes, such as atmospheric precipitation, loess formation, near-shore sediment transport, and surface exposure dating (SED) of rocks where 10Be has been produced in situ.

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