EXPLORING THE USE OF GAMMA-RAY SPECTROMETRY TO NON-DESTRUCTIVELY DETERMINE THE ABSOLUTE AGE OF FOSSILS

The enrichment of uranium in fossils is well documented, but most techniques used to produce absolute ages require partial destruction of specimens. By applying a new method of gamma-ray spectrometry to known radioactive samples, our team is seeking to determine the absolute age of fossils ranging from 13,000YBP- 54MYBP. Uranium ions commonly substitute for calcium ions in the bioapatite crystal lattice of bones. Bioapatite geochemical substitutions are dependent on the assumption that uranium is introduced rapidly post-mortem, enrichment occurs early in diagenisis, and bones and teeth remained closed with respect to uranium during geologic time. For this research, the isotopes ²³⁵U and ²³⁸U and various daughters including ²²⁴Ra, ²²⁶Ra, and ²¹⁴Pb, will be the focus for pulse height analysis of the gamma-ray spectrum produced by each specimen. Preliminary analysis using peak height ratios indicate that when the areas of peaks corresponding to daughter isotopes are added together, compared to the areas under peaks corresponding to parent isotopes, and plotted against logarithmic values of age, a nearly linear graph is produced. The consistent manner in which the peaks change from 13,000YBP to 54 MYBP shows phenomenologically that the different spectra serve as an indicator of time, and thus can produce estimate age dates.