AMS depth profiling of humidity in silica

Depth profiling measurements of light elements by Accelerator Mass Spectrometry (AMS) have been performed at the Forschungszentrum Rossendorf. Using the AMS facility at the 3 MV Tandetron accelerator, tritium depth profiles in carbon samples have been measured which had been exposed to the plasma at the first wall of the fusion experiments ASDEX-Upgrade in Garching/Germany, JET Culham/GB and TFTR Princeton/USA. Additionally, our AMS facility at the 3 MV Tandetron has been applied to depth profiling of humidity penetrated into as-implanted SiO2 layers. For this aim, Ge+ and Si+ ion implanted SiO2 layers (1014-1016 cm-2) were exposed to an artificial atmosphere with H218O humidity. AMS allows the discrimination of isobar atomic and molecular ions, thus depth profiles of O-, (OH)- and (H2O)- molecular ions could be investigated. By measuring the 18O or the H species of these molecular ions, the process of humidity penetration in as-implanted SiO2 has been studied. The high tritium inventory of the samples from the European fusion experiment JET required a dedicated AMS facility to prevent contamination of the versatile 3 MV Tandetron. Therefore, an SF6-insulated 100 kV tandem accelerator has been developed and applied to high dose tritium measurements. This facility has been also tested for depth profiling of light elements in radioactive samples.