A study of production of radioactive environmental reference materials used for proficiency testing program in Taiwan

• Seven kinds environmental materials were used to establish the production of the RMs.
• Spiking the traceable standard radioactive source to the blank substance.
• Each sample was carefully evaluated for its uncertainty.
• The performance of the RMs was estimated with the Proficiency Testing program report.
• The ability of the environment RMs in the configuration is quite good.

To realise radioactive environmental reference materials in Taiwan, seven environmental materials of soil, water, vegetation, meat, airborne particles (filter paper), milk and mushroom samples that are frequently encountered were used to establish the preparation of the reference materials. These seven environmental materials were collected, checked for freedom from radioactivity and prepared according to their properties. The preparation was carried out by using activity about 10–100 times that of the minimum detectable activity (MDA) in routine measurements in the radioactive standard used to spike the inactive material and this standard is traceable to national ionising radioactivity standards (TAF, 2004). To demonstrate sample traceability to the added standard, each sample was carefully measured and its uncertainty evaluated.Based on the recommendations of ISO Guide 35 for evaluation of reference materials and with the above assessment and verification procedures, the uncertainties (k=1) of the spike activity used in making reference materials were: 60Co≤4.6%, 134Cs≤4.7%, 137Cs≤5.0%, total β≤0.6% and 3H≤1.3%.