Geant4 Monte Carlo simulations for sensitivity investigations of an experimental facility for the measurement of tritium surface contaminations by BIXS

Abstract

A new experimental facility was built at the Tritium Laboratory Karlsruhe (TLK) to investigate tritium surface contamination on arbitrary solid samples. With the TRIADE facility samples can be exposed to tritium in a pressure range of 10−7–102Pa and a temperature range of 170–470K. Surface contamination which accumulate on the sample by adsorption or absorption processes of T2 are determined by β-induced X-ray spectrometry (BIXS). To quantify the amount of surface contamination and to study systematic effects of the setup Monte Carlo simulations have been performed. Detection efficiencies for tritium adsorption on all inner surfaces of the setup were determined. From that, a minimum detectable activity on the sample surface of 600Bq/cm2 has been calculated which can be translated into a minimum measurable surface contamination of 5.5×10−4 monolayer for ideal (100) gold surfaces. First tritium measurements with a gold-coated beryllium sample at exposure pressures of 5×10−3Pa showed an increasing background signal. After a dosage of p×t=(1.6±0.1)×10−2Pah the background signal was 1.10±0.04cps. Assuming an ideal plane (100) gold surface the results found can be translated into a surface contamination of ≈5.4×104Bq/cm2. Further measurements must be performed as a linear increase of the count rate with the applied dosage was observed.