The international reference system for beta-particle emitting radionuclides: Validation through the pilot study CCRI(II)-P1.Co-60.

The Bureau International des Poids et Mesures (BIPM) is developing a new transfer instrument to extend its centralized services for assessing the international equivalence of radioactive standards to new radionuclides. A liquid scintillation counter using the triple/double coincidence ratio method is being studied and tested in the CCRI(II)-P1.Co-60 pilot study. The pilot study, involving 13 participating laboratories with primary calibration capabilities, validated the approach against the original international reference system based on ionization chambers, which has been in operation since 1976. The results are in agreement and an accuracy suitable for purpose, below 5×10-4, is achieved. The pilot study also reveals an issue when impurities emitting low-energy electrons are present in the standard solution, which have a different impact on liquid scintillation counting compared to other primary measurement methods.

Test of a digitizer to process the pulse signal from the 3 photomultiplier tubes of a TDCR liquid scintillation counter.

The BIPM is developing a new service for international key comparisons in radionuclide metrology. The system, called ESIR, is based on a liquid scintillation counter using the Triple-to-Double Coincidence Ratio (TDCR) technique. The aim is to produce an international reference that can be reproduced over several decades of time in order to compare the calibration capabilities of National Metrology Institutes (NMIs). The maintainability of the electronics performing the signal processing is a challenge. To ensure the long-term sustainability of the electronics, the strategy is to set up redundant systems including at least one digital electronics module. The analogue modules developed in the 1990s and 2000s are less and less maintained and digital electronics are increasingly available on the market. In this context, a digitizer was tested and its suitability for the TDCR measurements compared to the currently used module based on an analogue front-end. This first implementation directly linking the photomultiplier anode to the CAEN digitizer without any analogue preconditioning shows a significant loss of detection efficiency and a lower signal to noise ratio observed on distributions of single photoelectrons. Although the TDCR method can correct for these efficiency losses, the loss of symmetry between the channels is too great to provide a sufficiently robust measurement. The use of low-pass filters upstream of the ADC will be considered to make this digital measurement system more reliable.

Fossil evidence for serpentinization fluids fueling chemosynthetic assemblages.

Among the deep-sea hydrothermal vent sites discovered in the past 30 years, Lost City on the Mid-Atlantic Ridge (MAR) is remarkable both for its alkaline fluids derived from mantle rock serpentinization and the spectacular seafloor carbonate chimneys precipitated from these fluids. Despite high concentrations of reduced chemicals in the fluids, this unique example of a serpentinite-hosted hydrothermal system currently lacks chemosynthetic assemblages dominated by large animals typical of high-temperature vent sites. Here we report abundant specimens of chemosymbiotic mussels, associated with gastropods and chemosymbiotic clams, in approximately 100 kyr old Lost City-like carbonates from the MAR close to the Rainbow site (36 °N). Our finding shows that serpentinization-related fluids, unaffected by high-temperature hydrothermal circulation, can occur on-axis and are able to sustain high-biomass communities. The widespread occurrence of seafloor ultramafic rocks linked to likely long-range dispersion of vent species therefore offers considerably more ecospace for chemosynthetic fauna in the oceans than previously supposed.

Separation of sedimentary micron-sized particles for palaeoceanography and calcareous nannoplankton biogeochemistry.

A protocol is described for separating sub-20 microm-sized particles contained in sedimentary rocks into size fractions. Geochemical data from manually isolated foraminifera are commonly used in the interpretation of marine palaeoenvironments; problems associated with the isolation of calcareous nannofossils hampers their geochemical exploitation. However, geochemistry performed on calcareous nannofossil monotaxic assemblages should provide more meaningful data sets than those generated from the highly heterogeneous bulk carbonate. This protocol is based on cascade filtering steps, using polycarbonate membranes with well-calibrated pores. Strong ultrasonic treatment can further be applied to selectively reduce the size of particles for greater enrichment. Obtained residues frequently comprise near-monotaxic nannofossil assemblages. The application of this technique, which can be achieved within less than 2 days, has provided distinct fractions of coccoliths, calcareous dinoflagellate shells and also diagenetic monocrystals. This protocol is designed for application in reconstructing the history of water-column physicochemistry and diagenesis. It also has the potential to provide insights into the biogeochemistry of calcareous nannoplankton, including vital effects.