We report experiments testing the question whether or not ultra-cold neutro
ns (UCN) stored in traps with total-reflecting walls are temporarily adsorb
ed to the walls. A hypothetical profess of sticking to the walls is theoret
ically intriguing but it can apparently make plausible the puzzling observa
tions made in UCN storage experiments over the years. (C) 2000 Elsevier Sci
ence B.V. All rights reserved.