A METHOD FOR RAPID INSITU EXTRACTION AND LABORATORY DETERMINATION OF TH, PB, AND RA ISOTOPES FROM LARGE VOLUMES OF SEAWATER
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abstract
An in situ pump and six channel extraction system, operating typically at 351 min-1, can not only filter seawater samples but also extract dissolved Th, Pb and Ra isotopes from large volumes of seawater at six different depths on a single lowering. By gamma counting the ash residues of three cartridges (one particle extractor and two nuclide extractors), we can determine 234Th and 210Pb concentrations in the particulate and dissolved phase. Extraction efficiencies for 234Th from the dissolved phase average 93 5% and for 210Pb average 90%. At the same time we can determine radium isotopic ratios precisely, but, at present radium concentrations can only be established by the determination of 226Ra in a 30-1 cohort sample. This system can be deployed easily from ships having an A-frame. It eliminates the problems of transporting and processing large volumes of samples and involves relatively little manual labor and analytical time. We have tested and used this device repeatedly in the Gulf of Mexico. Our preliminary results agree well with values of 234Th and 210Pb concentrations and 228Ra/226Ra activity ratios reported in the literature for the Gulf of Mexico. 1993.
