A characterization of radioactivity recovery rate of a pretreatment method is important to the radioactivity analysis. The recovery rate determines minimum detectable activity of the radioactivity analysis process which can represent a performance and reliability of the analysis result. In the case of paper, radioactive materials may be packaged, or they may contain tritiated vapor or ^14^CO~2~ if they have been exposed to a long time in the reactor environment. The combustion method has been widely used for detection of tritium (^3^H) or radiocarbon (^14^C) because it can simultaneously collect the both radionuclides and has high recovery rate. The combustion method is separating hydrogen and carbon atoms from a sample while slowly raising the temperature to a high temperature (\< 800 ℃), and simultaneously supplying air or oxygen to oxidize them and collecting them in the form of H~2~O and CO~2~, respectively. In general, the H~2~O is collected using dilute nitric acid and the CO~2~ is collected using an amine-based solution. This amine solution has been reported to be unstable because the collection structure is changed when too much CO~2~ is collected. Based on this, the recovery rates of paper sample were evaluated while the loaded amount of paper sample was changed by 1.0, 1.5 and 2.0. A diluted tritium standard source (Eckert&Ziegler) and ^14^C standard source solution (Perkin Elmer) were prepared and their radioactivities were 80.7 and 45.0 Bq/g, respectively. The source solutions were dropped on the sample boats with the paper sample by 0.5 mL each. The sample boats were loaded on a commercialized combustion and sample collecting system (Pyrolyser-Trio Furnace System, Raddec Ltd.) and heated up to 800 ℃. 0.1 M nitric acid and Carbo-Sorb E (Perkin Elmer) were used as collecting solution. Two scintillation vials were prepared for each sample. One vial was measured immediately, the other was shaken to give a physical impact and left for about 24 hours before mixing with the scintillation cocktail. The sample vial was prepared by mixing 8 mL of nitric acid and 12 ml of scintillation cocktail (Goldstar, Triskem) for ^3^H, and 5 mL of Carbo-Sorb E and 15 mL of the scintillation cocktail for ^14^C. The scintillation vials were measured using a liquid scintillation counter (Quantulus 1220, Perkin Elmer). The recovery rates when the scintillation vials were immediately prepared were 99.1±0.5, 97.9±0.6 and 99.3±0.6% for ^3^H, and 100.9±0.9, 93.8±0.9 and 91.5±0.9% for ^14^C, respectively. The recovery rates when the scintillation vials were prepared after leaving were 96.2±0.5, 99.1±0.8 and 93.9±0.6% for ^3^H and 97.2±0.9, 90.2±0.9 and 69.2±0.8% for ^14^C, respectively. In the case of ^3^H, there was no distinct relationship between loaded mass and recovery rate. Though there was a case (1.5 g) of increasing recovery rate after leaving, their correlation is ambiguous. For ^14^C, there was clear a relationship of loaded mass and the recovery rate, while the recovery rate was lowered when the mass of the sample was larger. Moreover, loss of radioactivity after leaving and giving the physical impact was intensified when the mass of the sample was larger. According to the stoichiometry, the bonding type of the captured CO~2~ can change, and the recovery rate may be drastically reduced due to unstable bonding at certain amount of captured CO~2~. Further work will be carried out on the detailed principles behind these findings in relation to the moles of hydrogen and carbon in the paper samples and bonding structure in the collection solution.


Radioactivity Recovery Rate of Paper Sample for 3h and 14c Based on the Combustion Method

Division / Sponsors: 
Power Division & Nuclear Engineering Division (NED)

Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

International Conference on Nuclear Engineering
Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

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