Beryllium-10

Beryllium-10 (¹⁰Be) is a radioactive isotope of beryllium. It is formed in the Earth's atmosphere mainly by cosmic ray spallation of nitrogen and oxygen.^[3][4][5] Beryllium-10 has a half-life of 1.387 million years and decays by beta decay to stable boron-10 with a maximum energy of 556.0 keV. It decays through the reaction ¹⁰Be→¹⁰B + e⁻. Light elements in the atmosphere react with high energy galactic cosmic ray particles; at such energies nucleons are knocked out almost at random, and any nucleus lighter than the original can remain.

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).

Beryllium-10

General
Symbol	10Be
Names	beryllium-10
Protons (Z)	4
Neutrons (N)	6
Nuclide data
Natural abundance	trace
Half-life (t1/2)	1.387×106 years[1]
Spin	0+
Binding energy	64976.3±0.08 keV
Decay products	10B
Decay modes
Decay mode	Decay energy (MeV)
β−	0.5560[2]
Isotopes of beryllium Complete table of nuclides

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 does not limit its residence time there.

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.^[6] 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. ¹⁰Be decay is a significant isotope used as a proxy data measure for cosmogenic nuclides to characterize solar and extra-solar attributes of the past from terrestrial samples.^[7]

The rate of production of beryllium-10 depends on the activity of the sun. When solar activity is low (low numbers of sunspots and low solar wind), the barrier against cosmic rays that exists beyond the termination shock is weakened (see Cosmic ray#Cosmic-ray flux). This means more beryllium-10 is produced, and it can be detected millennia later. Beryllium-10 can thus serve as a marker of Miyake events, such as the 774–775 carbon-14 spike. There can be an effect on climate^[8] (see Homeric Minimum). While other cosmogenic isotopes experience similar cycles, the high rate of production, long half-life, and relative immobility in the environment make this most suitable for this purpose.

See also

• Surface exposure dating

Lighter: Beryllium-9	Beryllium-10 is an isotope of beryllium	Heavier: Beryllium-11
Decay product of: lithium-11 (β−, n)	Decay chain of beryllium-10	Decays to: boron-10