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Beryllium-10 is the longest-lived of the seven known unstable isotopes of Be; it results mostly from the interaction of cosmic radiation, primarily neutrons, with a variety of target atoms by spallation, the splitting of nuclei (Lal 1988). It can also be produced at very low levels by radio-disintegration of U and Th (Sharma and Middleton 1989). Although all radioactive Be isotopes are produced in the atmosphere via cosmic-ray reactions (Arnold 1956; Lal and Peters 1967; Morris et al., Chapter 5, this volume), in this paper, we are most interested in 10Be produced in rock, which we refer to as in situ-produced. Such in situ-produced 10Be is a cosmic-ray dosimeter functioning as a quantitative monitor of near-surface residence time. In some geologic situations, 10Be can be used as a chronometer, allowing one to estimate the duration of surface exposure. In other settings, 10Be can be used as a tracer allowing one to estimate the rate, distribution, and behavior of Earth surface processes.
Rates of 10Be production are very low in rocks exposed at Earth’s surface, <101 to >102 atoms g−1 y−1 resulting in typical in situ-produced 10Be concentrations, termed activities, of 103 to 107 atoms g−1. The development of accelerator mass spectrometry (AMS) in the 1980s allowed routine measurement of 10Be at levels typical of rocks exposed near Earth’s surface (Elmore and Phillips 1987). Analytical refinements in the 1990s lowered detection limits by an order of magnitude, allowing dating of exposure periods <<103 years in favorable geologic and geographic situations (simple exposure histories at high altitude and latitude).
Most in situ 10Be is measured in quartz mineral separates where the primary spallation target is O (Lal and Arnold 1985 …