Improved measurement of the neutron absorption cross section for very low velocities

The absorption cross section of natural Gd and isotopic enriched 157Gd for ultra-cold neutrons (UCN) as a function of the velocity has been measured within a time-of-flight-experiment. Particular attention is paid to small velocities in the region of a few m/s. This is intended to determine the validity of the 1/v1/v-law governing absorption cross sections in this region and the resulting divergence at v=0v=0. The experiment does not show any significant violation of 1/v1/v for v>3 m/sv>3 m/s.