A comparative evaluation of 222Rn sealing materials for 226Ra analysis by gamma spectrometry

The accuracy of indirect measurements of 226Ra using gamma spectrometry critically depends on sealing techniques that prevent the escape of 222Rn (radon) generated within the sample. This study introduces a novel sealing method designed to overcome the limitations of conventional Rn sealing techniques. The Rn sealing performance of five sealing materials-silicone sealant, modified silicone sealant, butyl sealant, polyurethane sealant, and epoxy adhesive-was evaluated by sealing sample containers filled with Rn-containing water samples using each of the five materials, measuring Rn over time, and comparing experimentally estimated halflife of Rn for each sealed container with its physical half-life. Among the five sealing materials evaluated, the experimentally estimated half-life of Rn in samples sealed with modified silicone sealant, butyl sealant, polyurethane sealant, and epoxy adhesive, excluding silicone sealant, closely matched the physical half-life of Rn, demonstrating their reliable sealing performance. To verify the validity of the sealing method, the activity concentration of 226Ra was estimated in IAEA-434 phosphogypsum, a certified reference material, sealed with five different sealing materials. The results showed that for the four sealing materials, excluding silicone sealant, the measured values were statistically consistent with the certified value of IAEA-434, confirming the validity of the sealing method using these materials. The proposed sealing method enables accurate analytical results without requiring the complete filling of the measurement container, allows for visual inspection of the sample's filling state, and facilitates sample reuse for further analyses. These advantages make it a practical approach for the routine analysis of NORM and environmental samples.