Beryllium-10

Beryllium-10 (¹⁰Be) is a radioactive isotope of beryllium. It is formed mainly by the cosmic ray spallation of oxygen. Beryllium-10 has a half-life of 1.39 × 10⁶ years,^[2] and decays by beta decay to stable boron-10 with a maximum energy of 556.2 keV. It decays through the reaction ¹⁰Be→¹⁰B+e. Light elements in the atmosphere react with high energy galactic cosmic ray particles. The spallation of the reaction products is the source of ¹⁰Be (t, u particles like n or p):

¹⁴N(t,5u)¹⁰Be; Example: ¹⁴N(n,p α)¹⁰Be

¹⁶O(t,7u)¹⁰Be

Plot showing variations in solar activity, including variation in ¹⁰Be concentration which varies inversely with solar activity. (Note that the beryllium scale is inverted, so increases on this scale indicate lower beryllium-10 levels).

Because beryllium tends to exist in solutions below about pH 5.5 (and rainwater above many industrialized areas can have a pH less than 5), it will dissolve and be transported to the Earth's surface via rainwater. As the precipitation quickly becomes more alkaline, beryllium drops out of solution. Cosmogenic ¹⁰Be thereby accumulates at the soil surface, where its relatively long half-life (1.387 million years) permits a long residence time before decaying to ¹⁰B.

¹⁰Be and its daughter product have been used to examine soil erosion, soil formation from regolith, the development of lateritic soils and the age of ice cores.^[2] It is also formed in nuclear explosions by a reaction of fast neutrons with ¹³C in the carbon dioxide in air, and is one of the historical indicators of past activity at nuclear test sites.

References