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Setting-up of a Low-level Radon Reference Chamber Started


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 is currently being set up. For the dissemination of the unit at such low radon activity concentrations, a high-sensitivity transfer standard is being developed.

The reference volume of 0.5 m3 is based on a standard vacuum chamber. First measurements over a period of 8 days have shown absolutely no leakage of rare gas within the scope of a relative measurement uncertainty of ≤ 0.4 %. The data in the range above 1 kBq/m3 are in agreement with the data of the previous calibration fields (radon reference chamber, 50 l reference chamber).

An ADC board for the processing of the signals from the amplifier is one of the components of the high-sensitivity transfer standard which is to be developed for the dissemination of the unit. An FPGA module is located on the board, which processes the signal from the A/D converter further. A graphic user interface is generated by means of the Lab View software. The signals are represented and can be described with mathematical functions. High-frequency fractions are removed from the signal by software filters, so that the actual useful signal is clearly emphasised. Subsequently, the data is stored and analysed. An optimised pre-amplifier is being built on the basis of the results of first measurements which were performed using multi-wire pulse ionisation chambers. In addition, the data analysis within the software has been improved in order to filter noise signals.

Based on the results achieved up to now, it can be expected that the new calibration field will be available for customers in two years.