Effect of labile hydrogens on measurement of tritium preserved in hydrogens of cellulose

Isotopic fractionation of tritium in biological systems

Isotopic fractionation of tritium is a highly relevant issue in radiation protection and requires certain radioecological considerations. Sound evaluation of this factor is indeed necessary to determine whether environmental compartments are enriched/depleted in tritium or if tritium is, on the contrary, isotopically well-distributed in a given system. The ubiquity of tritium and the standard analytical methods used to assay it may induce biases in both the measurement and the signification that is accorded to the so-called fractionation: based on an exhaustive review of the literature, we show how, sometimes large deviations may appear. It is shown that when comparing the non-exchangeable fraction of organically bound tritium (neOBT) to another fraction of tritium (e.g. tritiated water) the preparation of samples and the measurement of neOBT reported frequently led to underestimation of the ratio of tritium to hydrogen (T/H) in the non-exchangeable compartment by a factor of 5% to 50%. In the present study, corrections are proposed for most of the biological matrices studied so far. Nevertheless, the values of isotopic fractionation reported in the literature remain difficult to compare with each other, especially since the physical quantities and units often vary between authors. Some improvements are proposed to better define what should encompass the concepts of exchangeable and non-exchangeable fractions.

A method for the determination of low-level organic-bound tritium activities in environmental samples

The authors discuss some of the difficulties encountered when analyzing organically bound tritium (OBT) and describe a sensitive method for low-level OBT determination in biological samples. The methodology, which combines suitable sample treatment, a combustion apparatus for large-sized samples and low-background liquid scintillation counting, provides exclusively carbon-bound tritium measurement. Two key points of this methodology are described and illustrated. The first one is the stage of removal of the exchangeable organic tritium. The efficiency of this stage, carried out by mixing powdered dry samples with tritium-free water, is evaluated. The second key point is the set of precautions taken at any stage of the treatment to avoid contamination of the samples by ambient atmospheric moisture. The detection limit of the method is about 0.5 Bq kg(-1) of dry material. Low-level applications of this methodology are given with estimation of the OBT/HTO ratios.