T01_P05

DETERMINATION OF CARBON-14 SPECIFIC ACTIVITY IN SOIL AND SEDIMENTS BY TUBE COMBUSTION AND LIQUID SCINTILLATION COUNTING METHOD

Krishnan K A¹,  S B¹, N K¹

¹Centre for Advanced Research in Environmental radioactivity (CARER), Mangalore, India

Carbon-14 (¹⁴C) is a pure beta emitter and occurs naturally in the environment due to cosmic ray induced production in the atmosphere. ¹⁴C is also released into the atmosphere by nuclear fuel cycle facilities and gaseous discharges from all types of nuclear power plants (NPPs).  Oxidation of the samples in a combustion system, trapping the produced CO₂ in an amine-based absorber, and subsequent liquid scintillation analysis (LSA) is a proven method for samples with high carbon content, such as terrestrial plants. However, for soil and sediment matrices, which are considered poor carbon pools, improved methods are to be adopted for combustion since a large mass of these samples is to be combusted to produce sufficient CO₂ for saturation of the absorber.

This paper reports an improved method in which the conventional tube furnace system is used for combusting soil and sediment samples collected from the clean air region and from the vicinity of a NPP. The produced CO₂ was absorbed in NaOH, precipitated as BaCO₃, and CO₂ was regenerated by acid hydrolysis of BaCO₃ in a specially designed regeneration setup and trapped in an amine-based absorber, mixed with a liquid scintillator, and subjected to LSA. Validation of the method was performed by combusting IAEA C3 reference material. The method is capable of yielding accurate results with a deviation of <2.2 % from the target value.Upon validation, the suitability of the method for the determination of small excess ¹⁴C activity in the vicinity of a nuclear power plant was demonstrated.