The PTB Contribution to the 1999 EURADOS Intercomparison of National Early Warning Systems

Abstract

The PTB operates an underground laboratory for dosimetry and spectrometry (UDO). It is situated at the Asse salt mine near Braunschweig, at a depth of 925 m below ground. Due to the low air kerma rate of less than 0.7 nGy.h -1 inside the laboratory, UDO is an excellent place for investigating the inherent background of radiation detectors and for providing 'background free' calibrations of highly sensitive environmental monitoring systems. The UDO laboratory has been involved in several EC-sponsored intercomparisons of environmental dose rate meters, electronic dosemeters, thermoluminescence dosemeters (TLDs) and spectrometers. The laboratory facilities and its role in the 1999 intercomparison of environmental monitors used in national networks of early warning systems, sponsored by EURADOS, are described. The experiments performed during this intercomparison gave the participants from seven countries the opportunity to determine the inherent background of their equipment as well as its linearity at very low dose rates, generated by different 137 Cs sources. In addition, the participants measured the photon energy dependence of their detector responses using collimated photon radiation fields produced by 241 Am, 57 Co, 137 Cs and 60 Co sources. The dose rates of these calibration fields are traceable to the PTB's primary standard measuring devices. Initial results of the measurements performed at UDO during this EURADOS intercomparison are presented.