  We develop a quasi-analytical theory for the quantum reflection amplitude of
Bose-Einstein condensates. We derive and calculate the decay-width of a
Bose-Einstein condensate. A general relation between the time-dependent
decay-law of the system and its quantum reflection amplitude allows us to
explain the quantum reflection anomaly of Bose-Einstein condensates present in
BEC-surface systems as a direct consequence of the repulsive particle
interaction.
