Evaluation of the fast neutron cross sections of 56Fe including complete covariance information

A new evaluation of all important neutron cross sections of 56Fe was performed in the neutron energy range 0.85-20 MeV, that is for the whole energy range above the resonance region. The evaluation combines the results of nuclear model calculations and the complete existing experimental data base in order to obtain the most accurate description of the cross sections possible within our present knowledge. The evaluation was performed in the following way: The cross sections from the EFF-2 file (results of model calculations) and their estimated covariances are used as prior information which is successively improved by adding experimental data and applying Bayes' theorem to obtain the posterior information. For this process the code GLUCS was used. As the results we obtained evaluated cross sections and their covariances for a chosen set of 12 independent cross sections. On the average the uncertainties of these cross sections are smaller by a factor of 2 to 3 than the uncertainties in the recent evaluated files ENDF/BVI and EFF-2. There are considerable correlations between the uncertainties for different cross-section types. This is a natural consequence of the existence of accurate experimental data on 'redundant''cross sections which enter as constraints into the described least - squares analysis. Our results confirm that the uncertainties for ENDF/B-VI and EFF-2, though derived by rather qualitative methods, are essentially correct. (orig.)