Comment on "Giant absorption cross section of ultracold neutrons in   Gadolinium"
  Rauch et al (PRL 83, 4955, 1999) have compared their measurements of the Gd cross section for Ultra-cold neutrons with an exptrapolation of the cross section for thermal neutrons and interpreted the discrepancy in terms of coherence properties of the neutron. We show the extrapolation used is based on a misunderstanding and that coherence properties play no role in absorption. 
J. Felber, R. Gaehler, R.Golub