An intercomparison on low-level radionuclide measurements in ground-level aerosol monitoring.

After the nuclear reactor accident of Chernobyl, the measuring system IMIS (Integrated Measurement and Information System for Monitoring the Environmental Radioactivity and Detecting Emissions from Nuclear Plants) was implemented in Germany. IMIS is a nationwide comprehensive measuring system which permanently monitors the radioactivity in all important environment media in the whole federal territory. At approx. 40 sites, the activity concentration of radioactive substances is measured in air and precipitations. 12 of these locations are survey stations for trace monitoring of radionuclides in the air. The legal bases of IMIS request regular inter-comparison analyses on reference materials prepared for quality assurance by the Federal coordinating laboratories in cooperation with PTB. In order to meet that requirement in the field of trace survey measurements in ground-level air, the Federal Office for Radiation Protection (BfS) and the Physikalisch-Technische Bundesanstalt (PTB) have conducted an inter-comparison with dust-loaded aerosol reference filters in 2005. The inter-comparison was organized in the framework of a co-operation of 6 trace survey stations from Austria, Germany and Switzerland. The paper describes the preparation of the real, dust-loaded aerosol filters, the procedure and device used for spiking the filters with a mixed activity standard solution containing Na‑22, Y‑88, Sr‑89, Sr‑90, Sb‑125, Ba‑133, Cs‑134, and Am‑241. The results and examples of uncertainty budgets will be presented and the conclusions drawn will be discussed