Ultra cold neutron life times in glow discharge cleaned bottles

Lifetimes of ultra cold neutrons in tubes made of various materials have been increased with improvement of surface cleanliness. With glow discharge cleaning in vacua of only 10-4 - 10-3 torr. life times for long storage periods were obtained that differ by less than a factor of 3 for quartz. Surface recontamination is slow at the achieved level and approaches a stable value well below that before cleaning. A temperature dependence of ultra cold neutron reflection loss rates was observed. A direct correlation between reflection losses and the surface hydrogen concentration was established. We conclude that for smooth surfaces of materials with low reaction cross section, losses are mainly caused by upscattering on tightly bound hydrogen. The probability is discussed that the remaining losses are due to still incomplete cleanliness of the surface caused by hydrogen recontamination from the bulk and the atmosphere. (orig.)