Modifications of the EFF-2 9Be evaluation

The EFF-2 9Be evaluation cross sections has been modified by changing its representation of energy-angle correlated neutron distributions stemming from the (n,2n) reaction. The presence of a sharp peak on top of a continuum distribution is a feature not encountered in other existing evaluations. Therefore processing tools cannot easily deal with this feature. A solution was found by representing part of the (n,2n) cross section as inelastic scattering (followed by neutron deexcitation) through the 2.429 MeV level in 9Be. Processing with existing tools leads to correct scattering matrices, but care has to be taken to ensure that the total (n,2n) cross section is obtained by explicit summation of two components indicated by MT16 and MT51. (author). 8 refs., 1 fig