Stuttgart 2012 – wissenschaftliches Programm
Q 42.2: Vortrag
Donnerstag, 15. März 2012, 10:45–11:00, V38.04
Durability of optical coatings in high purity tritium gas — •Sebastian Fischer and Kerstin Schönung — for the KATRIN collaboration. Karlsruhe Institute of Technology, Institute for Technical Physics - Tritium Laboratory, Karlsruhe, Germany
The aim of the Karlsruhe Tritium Neutrino (KATRIN) experiment is the model-independent measurement of the anti-neutrino mass. KATRIN measures the endpoint region of the electron energy spectrum of tritium beta decay where a non-vanishing neutrino mass has an influence on the shape of the spectrum. The beta electrons are produced in a windowless gaseous tritium source. In order to reach the design sensitivity of 200 meV/c2 (90% C.L.) the tritium concentration of the inlet gas is continuously monitored by a laser Raman system with 0.1% statistical uncertainty. The system uses an optical measurement cell which is located in-line in the tritium loop of KATRIN.
Tritium resistant optical coatings on all windows surfaces of the measurement cell are necessary to maintain a reliable and almost maintenance-free nonstop operation of the Raman system over 5 years of KATRIN measurements. However the up to now employed electron-beam deposited coatings were damaged after about 3 months of contact with a high purity tritium gas atmosphere (∼ 200mbar, > 90% purity). Therefore commercially available coating types are currently being tested in a dedicated COAting Test EXperiment (COATEX) by repeated exposures to tritium gas and subsequent measurements of their optical properties. In this talk an overview of COATEX will be given and results from the first series of exposures presented.