Development and validation of reference materials for tritium radioactivity analysis comparison programs

To enhance regional preparedness for radiological emergencies and improve the reliability of internal dose assessments, this study developed and validated tritium-spiked urine samples and low-level tritium reference materials. These materials were produced as part of a collaborative program within the Asia Dose Assessment Expert Network, aiming to standardize analytical methods for internal tritium exposure across Korea, China, and Japan. Urine samples were prepared by adding certified tritium reference material to a processed urine matrix, followed by rigorous evaluation of homogeneity and stability. Results from repeated measurements confirmed uniform distribution (maximum deviation within ±10 %) and minimal volatility over a three-month period. Analytical reliability was verified via blind testing using both direct and distillation measurement methods, with the root mean square error (RMSE) values of 5.06 % and 10.5 %, respectively. In parallel, low-level tritium reference materials targeting 5 Bq/kg were produced through a six-step gravimetric dilution using a certified tritium stock solution. Homogeneity and activity concentration were assessed using one-way ANOVA and considering a quench correction with a low-level liquid scintillation counter. The standard uncertainty of detection efficiency was estimated at 1.5 % (68 % confidence level), and comparison with the internal standard method showed an efficiency bias of only 0.2 %. The validated reference materials and quality evaluation protocols presented in this study provide a robust foundation for harmonizing tritium bioassay techniques in East Asia. These outcomes are expected to support future efforts in standardizing internal exposure assessment methods and establishing a regional cooperative monitoring framework.