Sampling and Analytic Schemes for U-, Th-series and Be Isotopes

Teh-Lung Ku and Shangde Luo

  1. Sampling

    (a) Type of samples
    Dissolved and particulate radionuclides in ca. 1,500 liters of water collected by in situ pumps equipped with a filtration system and Fe-Mn adsorber.
    Dissolved radioactive and stable elements in 30 liter samples (rosette sampler). Sediment trap samples.

    (b) Cruises: Two survey cruises.

    (c) Stations: 13 stations along the 140° W line.

    (d) Approximate sampling depths: 0, 25, 50, 95, 140, 215, 340, 440, 535, 630 and/or 800 m.
  2. Analyses

    (a) In situ (MULVFS) pump samples:
    Radionuclides collected on the Fe-Mn adsorber will be leached off in acid solution. After addition of spikes and removal of Fe and Mn, the samples will be analyzed by gamma spectrometry for Be, Ra, and Th. Then, Th, Th, and Be will be measured by alpha spectrometry and accelerator mass spectrometry. After about one year, Ra will be measured via the ingrown Th using alpha spectrometry. Particulates on the filter paper (> 1µm) will be digested with acids and measured for Be, Th, Th and Pb by gamma spectrometry. Particulate Th, Po, Be, as well as Th (redundancy measurement), are measured by alpha spectrometry and accelerator mass spectrometry.

    (b) Rosette-sampler samples:
    About 1 liter of water each will be analyzed for dissolved Be (by gas chromatography) and Th (by mass spectrometry). For the remainder of samples (~20 l), Ra will be measured by the Rn emanation method or by gamma spectrometry.

    (c) Sediment trap samples:
    Sediment trap samples are dried and counted for gamma ray activities (Be, Th, Pb, and Th). They are then digested with acid and measured for Th, Po, Be, and Th (redundancy measurement) by alpha spectrometry and accelerator mass spectrometry.
  3. The samples for dissolved and particulate radionuclides collected by in situ pump will be provided by Dr. J. Biship. The sediment trap samples will be furnished by Drs. S. Honjo and J. Dymond.

  4. Intercalibration and interlab comparison:

    Th and Pb data derived by gamma spectrometry for particulate (filtered and sediment-trap) and soluble fractions will be compared with those measured by the University of Washington group using the beta counting methods. Sandards prepared from `old' sediments are to be used to calibrate alpha and gamma counting systems, by comparing pairs of nuclides in secular equilibrium, such as U with Th, and Pb with Po. Interlaboratory calibration is planned for the measurements of Pb, Po, Th, Th and Be.