Long term comparison of methods to sustain energy calibration in low level gamma-ray spectroscopy and investigation of possible sources for drift.

Two methods to compensate the gain drift of low level gamma-ray spectrometers are compared. For a period of 4 years, source injection and pulser method have been applied in parallel. The long term stability of a reference peak, injected by a precision pulser, has been validated by periodical source injection to sustain the energy calibration. The pros and cons of both methods and the advantage of active vs. passive energy calibration are discussed. The main cause for gain drift and the critical components have been identified.

Enhancing sensitivity of portal monitoring at varying transit speed.

The sensitivity of a portal monitoring system has been improved by introducing speed dependent integration time in the data processing of the count rate signal. Characterization and first tests have been performed using a pneumatically driven (137)Cs point source, before deploying the system to a test point at a railway junction near Vienna. At 14m/s the MDA could be reduced by a factor of two and at 28m/s by a factor of three compared to a fixed integration time of 1s, whereas high sensitivity at low speed remained unaffected.

Optimization of an active anti cosmic veto shielding.

The active veto shielding of a low-level gamma spectrometer has been optimized to reduce the background in the interval 20-2700 keV by a factor of nine. The signal to noise ratio was increased, due to the reduction of electromagnetic interference coming from the power line, by using an uninterruptible power supply and specially designed line filters. The overall performance of the veto shielding was improved by using time spectroscopy to find the optimum time duration for the coincidence window.

A ultra low level laboratory for nuclear test ban measurements.

The radionuclide laboratory at the Austrian Research Centers Seibersdorf (ATL03) was installed to support the international monitoring system for verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT and Text of the establishment of a Preparatory Commission for the Comprehensive Test-Ban-Treaty Organization, 1996). Therefore, the background of a high-purity germanium detection system has been reduced by developing a high sophisticated active and passive detector shielding. The entire system is encapsulated in an iron-castle and placed into a fall-out shelter. The final count rate, achieved over the energy interval from 40 to 2700 keV, amounts to 0.18 counts s(-1) kg(-1) (Ge).