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Setting-up of a low-level radon reference chamber


In order to calibrate measuring devices for the determination of the Rn-222 activity concentration in air in the range below 1000 Bq/m3 in a traceable way, a low-level radon reference chamber was set up. This chamber consists of a traced-back volume for the generation of the reference atmosphere, a facility for the generation and transfer of defined activity, and a highly sensitive transfer standard for the maintenance and the dissemination of the unit.

The setting up of a radon emanation measuring facility for the transfer of defined activity has been completed and is now available as an additional primary procedure for the realization of the unit of activity concentration in Bq/m3.

With this measurement procedure, constant reference atmospheres are generated. For this purpose, the radon emanated from a radium-226 activity standard is transferred, via a noble-gas-tight circuit, into a reference volume. Traceability of the activity concentration is thus realized via the radium activity A(Ra-226), the emanation degree χ and the volume V.

In order to determine the emanation power of the radium-226 activity standard, an emanation measuring facility based on γ spectrometry was developed. Within the scope of the doctoral dissertation on the Development of a low-level radon reference chamber, several emanation sources were produced and characterized. The eight existing emanation sources of different activity allow stable reference atmospheres from 150 Bq/m3 to 1900 Bq/m3 to be generated so that now, also commercially available measuring instruments can be used to carry out a long-term calibration (t > 5 days).