Determination of¹⁴C in environmental materials: Combination of CO₂ absorbent and a large-volume low-background liquid-scintillation counter

Abstract

Commerically available CO₂ absorbent and its scintillator were used to determine¹⁴C in environmental materials. Absorption of CO₂ by the CO₂ absorbent was quantitative, and strong and stable fixation was confirmed by no release of CO₂ from the CO₂ absorbent for a long period after absorption. The¹⁴C activity was measured by a large-volume low-background liquid-scintillation counter and the counts were quite stable for two weeks. Counting efficiency and background counts varied with the amounts of CO₂ absorbed, indicating a change of quenching level with absorption of CO₂. The different quenching levels were, however, normalized with external standard channel ratio (ESCR). Specific activity of¹⁴C in the present shell was evaluated for samples with different amounts of CO₂ absorbed and were consistent with each other within the counting error, suggesting validity of the present method. Contemporary¹⁴C level in the environmental materials, 95% CO₂ saturated sample, could be measured with 4% counting error (2σ) by 1000 min counting time.