A Ultra Low Level Radionuclide Laboratory to Support the Comprehensive Nuclear Test Ban Treaty Organisation (CTBTO)

The Protocol of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) calls for Radionuclide Laboratories certified by the Technical Secretariat to support the international monitoring system (IMS) for verification of the Treaty. Therefore a Radionuclide Laboratory at the Austrian Research Centers Seibersdorf (RL3) was installed. To achieve the demanded minimum detection limit of 5 µBq/m³ for Ba-140 (537 keV), the RL3 was constructed as a low level laboratory. The background of a high-purity Germanium detection system (HP-Ge) has been reduced by developing an active and passive detector shielding. The entire system is encapsulated in an iron-castle and placed into a fall-out shelter. The influence of radion was reduced by the installation of an air-conditioning system. The final court rate, achieved over the energy interval from 40 keV to 2700 keV, amounts to 0.18 cps. The reduction factor, compared with the outdoor count rate, is approximately to 10³. Hence, the demanded detection limit for Ba-140 will be achieved by using a minimum measurement time of 24 hours.