[en] The tangential beam T 7 of the BR-2 reactor is equipped with a slow chopper facility which is designed for the measurement of neutron cross-sections in the energy range from 2 to 150 meV. The chopper facility has operated since 1967 by the Central Bureau for Nuclear Measurements in cooperation with the Studicentrum voor Kernenergie. So far, the chopper facility was used in the framework of the programme on the measurement of neutron data for nuclear fission reactor design. Typical experiments are well documented by the work of A. Deruytter on: ''The accurate fission cross-sections of ²³⁵U and ²³⁹Pu from 0.002 to 0.15 eV and the reference value at 2.200m/s''. Measurements of this type are the basis for normalization of numerous measurements performed in relative units in this and higher energy ranges and furthermore contribute to a more consistent insight and error reduction in many related thermal reactor data such as fission ratio's, neutron yield per absorption, etc. (author)