Silicon has nine isotopes, with mass numbers from 25-33. 28Si
(the most abundant isotope, at 92.23%), 29Si (4.67%), and 30Si
(3.1%) are stable; 32Si is a radioactive isotope produced by
argon decay. Its half life, after much argument, has been determined to
be approximately 276 years (DeMaster,1980), and it decays by beta emission
to 32P (which has a 14.28 year half-life) and then to 32S.
Silicon isotopic ratios are compared to the NBS 28 standard for measurement.
32Si has seen use in dating biogenic silica, primarily in sea
shells. This nuclide might be very useful for determining sedimentation
rates of marine sediments containing biogenic silica. 32Si concentrations
in rainwater vary seasonally. Dansgaard et al. (1966) found a relationship
between 32Si and 90Sr, indicating that 32Si
could be used to date glacial activity.
Source of text: This review was assembled by Dan Snyder,
primarily from Faure (1986).
||>Dansgaard, W., Clausen, H. B., and Aarkrog, A. (1966). "Evidence
for bomb-produced silicon". J. Geophys. Res., 71: 5474-
||DeMaster, D. J. (1980). "The half-life of 32Si determined
from a varved Gulf of California sediment core." Earth and Planet.
Sci. Letters, 48: 209-217.
||Faure, G. (1986). Principles of Isotope Geology, Second Edition.
John Wiley and Sons, New York. 589 pp.
||Hoefs, J. (1987). Stable Isotope Geochemistry, Third Edition.
Springer-Verlag, New York. 241 pp.