Determination of Thorium-230 and Protactinum-231 in Ocean Waters by Isotope-Dilution Mass Spectrometry

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9415562 BACON The primary objective of this project is to develop a new procedure for the chemical analysis of seawater that will permit the naturally occurring radionuclides thorium-230 (half-life 75,000 years) and protactinium-231 (half-life 32,000 years) to be measured in the same sample. The new procedure will employ mass- spectrometric techniques of measurement and is intended to replace currently used procedures based on alpha-spectrometry. It is expected that significant improvements in sensitivity, precision, and speed of analysis will be realized. The reasons for the special focus on this particular pair of radionuclides are that (1) they provide unique information about the flux of particular matter in the oceans and the scavenging processes that regulate the level of a number of chemical species, and (2) they can be important tools for deciphering the sedimentary record of climate over the last glacial cycle. Improved data on the distributions of the two radionuclides will permit better testing and validation of their use as oceanographic tracers. After the new procedures are perfected, a study of the distribution of thorium-230 and protactinium-231 in the western North Atlantic Ocean will be undertaken. This part of the project will provide a full-scale demonstration of the new procedures and is expected to reveal features of the distribution that cannot presently be resolved.