Lead-radium dating improved
Mass spectrometry improves lead-radium dating
CJFAS - Publication year 1999
Application of an ion-exchange separation technique and thermal ionization mass spectrometry to 226Ra determination in otoliths for radiometric age determination of long-lived fishes
To improve the accuracy and precision of radiometric age determination using lead-210:radium-226 disequilibria in otoliths of fishes, a technique was developed incorporating an ion-exchange procedure followed by isotope-dilution thermal ionization mass spectrometry (TIMS) to determine radium-226. This technique counts ionized radium atoms directly; therefore, the uncertainty of the technique is superior to conventional radio-decay dependent techniques. Calcium and barium are major components of the otolith matrix that can interfere with TIMS analysis of radium. To remove these interferants, an ion-exchange separation procedure was developed. This procedure was tested by applying it to otolith samples from three fish species in three separate radiometric ageing studies. The resultant separations and TIMS determinations indicate that the procedure efficiently separates radium from calcium and barium. Measured radium-226 activities for each species were similar to previous radiometric ageing studies, with the exception of one sample. When results were compared with traditional radium-226 determination techniques, radon emanation and α-spectrometry, the separation procedure with isotope-dilution TIMS had significant advantages. Samples over three times smaller than attempted in other studies were processed with decreased uncertainty and processing time.
Andrews, A.H., K.H. Coale, J.L. Nowicki, C. Lundstrom, Z. Palacz, E.J. Burton, and G.M. Cailliet. 1999. Application of an ion-exchange separation technique and thermal ionization mass spectrometry to 226Ra determination in otoliths for radiometric age determination of long-lived fishes. Canadian Journal of Fisheries and Aquatic Sciences 56: 1329–1338.
Publication:
This was one of two papers that resulted from my Master of Sciences in Marine Science through Moss Landing Marine Laboratories (California State University).
M.S. Thesis:
Image of whole juvenile otolith from a Pacific grenadier (left) used as a guide in the core extraction from adult otoliths (right) to the proper size and mass. Lead-radium dating was not possible as a complete application to otolith cores prior to mass spectrometry.
