MEASUREMENT OF AMBIENT CARBON-14 BY USING THE GEL SUSPENSION COUNTING METHOD

For monitoring the ambient 14C, the CaCO3 suspension counting method was established in this work. In the preparation of CaCO3 powder, a two-stage sampler with 3 mol L-1 NaOH absorbent was designed to collect the ambient CO2 at a sampling flow rate of 1 L min-1, and then the CaCO3 was precipitated by adding saturated CaCl2 solution. By using 2 g of CaCO3 powder, 4 mL double-distilled water and 14 mL scintillation cocktail, the lower limit detection could reach 20.0 mBq m-3 by using a commercially available low background liquid scintillation counter. Co-comparison experiments showed that the activity concentration of 14C measured by the gel suspension counting method consisted well with the results of other three methods. It indicates that the CaCO3 suspension counting method is also a practical method for routine monitoring of ambient 14C.