The influence of deuterium exposures on subsequent outgassing rate of an UHV system

The accuracy of results in experiments where a well-processed UHV system is exposed to hydrogen depends on the hydrogen absorption rate and kinetics of subsequent spontaneous release from the system itself. In experiments to date, the sensitivity required to detect very low rates has been achieved only when tritium has been used as a tracer gas. Unfortunately, tritiated water from the surface prevails among released gas species which is not expected for well-outgassed surfaces. In the present studies, UHV system behaviour at 303 K during three deuterium exposures of duration 92 and 72 h at an initial pressure of 1 mbar was explored. The rate of decrease of pressure was constant during the whole of these periods as monitored by non-ionizing vacuum gauges. It corresponded to an effective sticking probability of the order of 1×10-12 and resulted in absorption of 5×1014 D atoms/cm2. The release kinetics were observed for several days starting immediately after deuterium had been pumped from the system. Initially, the deuterium release rate exceeded the background hydrogen outgassing by more than three orders of magnitude. These results demonstrate that extremely high sensitivity for deuterium absorption and release can be achieved with a precise pressure measuring technique otherwise attributed exclusively to tritium scintillation methods.