Silicon-32 as a tool for dating the recent past

Silicon-32, with a half-life of approximately 140 years, has the potential to fill the dating gap that lies between those chronologies based on the shorter-lived isotopes of (3)H and (210)Pb, and those based on the longer-lived (14)C. Silicon-32 is produced in the atmosphere by cosmic ray bombardment of argon, and falls out on the Earth's surface in precipitation. Silicon-32 methods may be used to date siliceous sediments and sponges, groundwater and glacier ice. Measurement of (32)Si concentrations in these archives is, however, not straightforward. Two methods are available: radioactive-decay counting of the activity of the daughter nucleus, (32)P, and accelerator mass spectrometry, but in both cases the detection of (32)Si pushes the boundaries of the technique. Even the half-life of (32)Si is not known to a precision of better than +/- 10%. In this paper, we review efforts to determine the isotope's half-life, survey the detection methods and discuss the applications of (32)Si chronology. We show that at least some of the chronometric potential of this radioisotope is close to being realised as a result of recent improvements in methods of measurement. (C) 2009 Elsevier Ltd. All rights reserved.