Sironić, Andreja; Krajcar Bronić, Ines; Kožar Logar, Jasmina; Krištof, Romana
(2019)
Organically bound tritium (OBT) interlaboratory comparison results.
In: Popić, Jelena; Coha, Ivana; Krajcar Bronić, Ines; Knežević Medija, Željka, (eds.) Zbornik radova Dvanaestog simpozija Hrvatskog društva za zaštitu od zračenja. Zagreb, Hrvatsko društvo za zaštitu od zračenja, pp. 364-369
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Abstract
Samples from two international interlaboratory exercises on activity of organically bound tritium (OBT) in biological material were analysed by laboratories at the Jožef Stefan Institute (JSI) in Ljubljana and at the Ruđer Bošković Institute (RBI) in Zagreb.
In the 4th International OBT exercise a sample of dried grass from a vicinity of the Nuclear Power Plant Cernavoda, Romania, was distributed among the participants of the OBT group of interested laboratories. In the 5th International OBT exercise a dried fish from vicinity of Chalk River Nuclear Power Plant, Canada, was distributed and the results were obtained from 24 laboratories. The JSI Laboratory runs OBT analyses on regular basis. For the RBI Laboratory the 4th exercise served as guidance for adaption of the sample preparation procedure and the 5th one served as a confirmation on suitability of sample preparation procedure for OBT.
The activity of OBT in a sample is measured in water produced by oxidation of organic material and can be expressed as Bq/l of combustion water. It can also be calculated as Bq/kg of dried material by using hydrogen percentage. The consensus values provided by the organizers were: (479 ± 15) Bq/l of combustion water, (247 ± 8) Bq/kg of dried sample and (5.67 ± 0.01) % of hydrogen for grass sample, and (32.8 ± 3.7) Bq/l combustion water, (22.6 ± 5.5) Bq/kg of dried sample and (7.66 ± 0.01) % of hydrogen for the fish sample.
The results from the JSI and RBI laboratories were evaluated by z-score and statistical tests. The JSI laboratory provided satisfactory results in both exercises, while the RBI laboratory had questionable (z-score) and non-acceptable ( value) results in the 4th exercise, while both values were acceptable in the 5th exercise. The main reason for the poor performance on the 4th exercise was identified as a large reported uncertainty, mainly due to variation in the preparation procedures while searching for the optimal conditions and to large dilution factors during measurement in LSC. Based on the experience gained in the 4th intercomparison exercise, the sample preparation procedure at RBI was adapted and optimized, and the results of the 5th exercise were satisfactory.
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