The method of radiative capture analysis with ultra-cold neutrons (UCN) was
used to investigate the UCN interaction with the surface of the materials
usually employed in UCN physics. The values and upper limits which were obt
ained for the capture probabilities for homogeneous media were in accordanc
e: with the standard theory. New results for alloys confirmed the existence
of a selective enhancement effect. (C) 2000 Elsevier Science B.V. All righ
ts reserved.