Decay/ingrowth uncertainty correction of ~(210)Po/~(210)Pb in seawater

摘要

Due to increasing application of ~(210)Po/~(210)Pb in studying particle dynamics, a consistent procedure and calculation to derive accurate and precise result of ~(210)Po and ~(210)Pb in seawater should be proposed in the framework of intercalibration by GEOTRACES. The associated uncertainty of radioactivity, which is a significant component of data report, plays a vital role in intercomparison and should be well evaluated. Although measurement uncertainty of laboratory result was well defined in ISO standards and IAEA technical documents, the decay/ingrowth uncertainty correction from laboratory result to in-situ result was less studied. It was demonstrated that the relative uncertainty of in-situ ~(210)Pb activity was independent of elapsed time and equal to relative uncertainty of laboratory measuring ~(210)Po activity at second spontaneous deposition date. The relative uncertainty of in-situ ~(210)Po activity decreases with in-situ activity ratio of ~(210)Po to ~(210)Pb and increases with elapsed time between sampling date and separation date, relative uncertainty of laboratory measuring ~(210)Po activity at first spontaneous deposition date and relative uncertainty of in-situ ~(210)Pb activity. It was more important to improve precision of ~(210)Po at first spontaneous deposition date than that of ~(210)Po at second spontaneous deposition date. To obtain a desirable relative uncertainty of in-situ ~(210)Po activity, the maximum allowing elapsed time for ~(210)Po, which was important for sampling strategy making and quality assurance, was calculated by in-situ activity ratio of ~(210)Po to ~(210)Pb and precision of analytical method for ~(210)Po. The methodology of decay/ ingrowth uncertainty correction could also be applied for other radionuclide pairs (~(234)Th/~(238)U, ~(90)Y/~(90)Sr, ~(210)Bi/~(210)Pb), sample matrixes (aerosols), and disciplines.