Optimisation of CO2 absorption and liquid scintillation counting method for carbon-14 specific activity measurement in atmospheric air. (June 2021)

• Record Type: Journal Article
• Authors: Bharath, S.; Arya Krishnan, K.; D'Souza, Renita Shiny; Rashmi Nayak, S.; Ravi, P.M.; Sharma, Rajveer; Kumar, Pankaj; Chopra, Sundeep; Karunakara, N.
• Is Part Of: Applied radiation and isotopes. Volume 172(2021)
• Publication Date: 2021-06
• Subjects: Carbon-14 (14C) -- Optimisation -- Liquid scintillation counting (LSC) -- Atmospheric air monitoring -- Saturation; Radiology -- Periodicals; Radiation -- Industrial applications -- Periodicals; Nuclear chemistry -- Periodicals; Internet resource; Periodical; 660.298
• DOI: 10.1016/j.apradiso.2021.109685
• Languages: English
• ISSNs: 0969-8043

Abstract

Abstract: A method for the determination of 14 C activity in the ambient air was optimised with the development of a simple setup for the regeneration of CO2 from carbonate sample and saturating the absorber in <45 min for direct determination of activity by liquid scintillation counting (LSC). Atmospheric CO2 was trapped in NaOH solution and precipitated as BaCO3 by adding BaCl2 . The carbonate sample was taken in a newly designed regeneration system, subjected to acid hydrolysis, and the absorber (CarboSorb-E) was saturated with the CO2 regenerated from carbonate sample. This allowed optimisation of CO2 absorption by the absorber (up to ~ 2.3941 g of CO2 /10 mL with an average of 2.1688 g) and a minimum detectable activity value of 14 Bq kg −1 C for a counting time of 300 min (8 Bq kg −1 C for 1000 min) was achieved with Quantulus - 1220 LSC system. The necessity of (i) the measurement of the total volume of air sampled, (ii) the determination of trapping efficiency for CO2 in the NaOH, recovery of 14 C in chemical processing of BaCO3, and subsequent regeneration and absorption processes, and (iii) independent determination of carbon content in the air for expressing the results in terms of 14 C specific activity (Bq kg −1 C), are avoided in this method. The method is capable of yielding accurate results, in a considerably shorter time when compared to previously reported methods, with a deviation of <2.2% from the target value (with a relative standard deviation of 1.1%, and a relative error of 0.53%) when ambient air samples from clean air region (region not affected by local anthropogenic sources of 14 C) are analysed. Validation of the method was performed by (i) analysing BaCO3 sample derived from ambient air by accelerator mass spectrometry, and (ii) analysing the CO2 produced from the combustion of IAEA C3 reference material. Upon validation, the suitability of the method for determining small excess 14 C specific activity in the vicinity of a nuclear power plant was demonstrated. Highlights: Method based on CO2 absorption in absorber & LSC counting for the determination of a 14 C in the atmospheric air was optimised. A simple system was developed for the regeneration of CO2 from carbonate sample & the saturation of the absorber in <45 min. MDA value of 14 Bqkg −1 C for a counting time of 300 min was achieved. Small excess a 14 C in the vicinity of the nuclear power plant was quantified successfully.