Modification and decay of radiation defects in tooth enamel
EMSL Project ID
2529
Abstract
Stable carbonate radicals created in tooth enamel by ionizing irradiation from soil are used in dating palaeontological artefacts up to Megayears. The number of radicals as measured with electron spin resonance (EPR) is taken proportional to the acquired dose. Thermal decay of radicals (fading) is not taken into account. Recent works (e.g. [O.I.Scherbina, A.B.Brik, Appl. Radiat. Isot.,52, 1071, 2001; A.Skinner et al., Quat.Sci.Rev. 20, 1027, 2001]) have shown that EPR spectra of enamel change with age expressing modifications in the structure of hydroxyapatite crystals. Our working hypothesis is that CO2-radical-molecules can move from their initial sites of orthorhombic or axial symmetry to the more symmetric sites (e.g. tumbling in occluded water)[G. Liidja, Phosphorus Res. Bull., 10, 341, 1999; Proc. Estonian Acad. Sci. phys.-math., 50, 227, 2001]. A careful study of Q-band EPR spectra of stepwise heated enamel should reveal whether transformations of radicals could be described by Arrhenius type plots. If the answer is positive, it can be used to improve EPR dating reliability. The planned investigation needs a well functioning Q-band EPR spectrometer. It is known that quantitative measurements in Q band are complicated as compared to X-band work, but our preliminary investigations have shown that the spectral resolution in X-band is not high enough to resolve the complicated band structure of irradiated bioapatite even when using sophisticated deconvolution methods. Samples: Irradiated and grained enamel in quarz vials (about 5 to 10 mg). Measurements: Q-band ?EPR spectra in continuous regime at room temperature but at several microwave power values. Specific needs: A small furnace for heating samples between measurements (controlled temperatures up to +400 deg Celsius +-2C). Data acquisition: Users laptop (Toshiba Satellite 2180CDT equipped with ORIGIN 6.0) directly or via the EMSL computer system.
Project Details
Project type
Exploratory Research
Start Date
2002-10-01
End Date
2003-10-24
Status
Closed
Released Data Link
Team
Principal Investigator
Related Publications
Poster presentation at the annual meeting of the American Society for Bone and Mineral Research