Evaluation of covariance data of JENDL

Iwamoto, Osamu  

One of the main topics of JENDL-4.0, was the enhancement of covariance data. Especially for actinides, they were evaluated and adopted to the all data of resonance parameters, reaction cross sections, fission neutron spectra, and the number of fission neutrons. The covariance matrices were evaluated based on experimental data and evaluation methodology of the evaluated data. The fission cross sections, for which experimental data were abundant, were evaluated using least-square method resulting in the most probable value as well as a covariance matrix. For the cross sections that were evaluated using nuclear model calculations, the covariance matrices were obtained using model parameter sensitivities. The methods and results of the covariance evaluations in JENDL-4.0 will be presented with recent progress of ongoing efforts on the covariance evaluation of non-actinides of JENDL-4.0.