Gas system

The measurement of the singlet capture rate in hydrogen gas not only requires the production of ulta-pure and monoisotopic protium on the level of $c_{Z>1}\sim 10^{-8}$, but this purity must also be maintained and monitored throughout the whole period of data taking. In order to meet these requirements we have built and tested an elaborate gas handling apparatus based on chemical purifying methods and equipped with chromatographic analysis systems. Also the circulation of the protium during the running combined with removal of impurities is in preparation. The protium is produced by electrolysis of deuterium-depleted water combined with Palladium filtering. All this equipment and the test results of its performance are described in several sections of this chapter.

Maintaining the ultra-high purity level of 10$^{-8}$ turns out to be at least as difficult as reaching these levels, because many commonly used materials employ outgassing rates exceeding within short periods the tolerated levels of contamination. Especially water vapour, N$_2$, CO, O$_2$, CO$_2$ and Hydrocarbons (usually in this order) are the main gases to be kept under control. We have done extensive vacuum, baking and material tests described in the following chapter.

Our general conclusion is that the whole hydrogen part of our apparatus must be designed of bakeable and low evaporation material, like metals, metal oxydes and glasses, and the evacuation must be performed using an UHV suitable oil free vacuum system. Our proposed final setup is designed according to these specifications, and our test results indicate that we can meet the stringent requirements of high purity.