Evaluations of the fast neutron cross sections of 182,183,184,186W and 181Ta including complete covariance information

Abstract

New evaluations of all important neutron cross sections of 182,183,184,186 Wa nd 181 Ta were performed from the upper end of the resonance region (2.2-12keV) up to 20MeV. The evaluation combines the results of recent nuclear model calculations (prior) and the complete existing experimental data base by means of the Bayesian code GLUCS06 in order to obtain the most accurate description of the cross section (posterior) within our present knowledge. As result of this work we obtained improved file 3 (cross sections) and file 33 (covariances) data for all important reactions of fast neutrons with the mentioned nuclides. Whenever necessary and possible fine structure of cross sections (at low neutron energies) was superimposed on the GLUCS results for the cross sections in a final evaluation step. For the isotopes of W complete new evaluated general purpose files in ENDF-format were produced by combining our evaluation results (files 3 and 33) with existing resonance data from JENDL 3.3 and file 4 and 6 data (energy-angle distributions for secondary particles) from our prior. These evaluations have been accepted for the Joint European Fission and Fusion File JEFF-3. For Ta a complete new evaluated file based on the described evaluation of cross sections and covariances will be produced in near future and submitted to JEFF-3.