Experimental data shows anomalously large Ultra Cold Neutrons (UCN) reflection losses and that the process of UCN reflection is not completely coherent. UCN anomalous losses under reflection cannot be explained in the context of neutron optics calculations. UCN losses by means of incoherent scattering on material defects are considered and cross-section values calculated. The UCN capture cross-section on material defects is enhanced by a factor of 10^4 due to localization of UCN around defects. This phenomenon can explain anomalous losses of UCN.
@article{arxiv.nucl-ex/0408010,
title = {UCN anomalous losses and the UCN capture cross-section on material defects},
author = {A. Serebrov and N. Romanenko and O. Zherebtsov and M. Lasakov and A. Vasiliev and A. Fomin and I. Krasnoshekova and A. Kharitonov and V. Varlamov},
journal= {arXiv preprint arXiv:nucl-ex/0408010},
year = {2009}
}