What Is the Real PFNS of ²³⁵U at Thermal Point?

Abstract

The traditional assumption of prompt fission neutron spectra (PFNS) integrated over emission angle applies for any calculation of the neutron interaction inside fissile material. Only these evaluated data are included in any neutron data library. But this is not correct. Prompt fission neutrons have very strong angular energy distribution relative to fission fragment (FF) direction. The FFs have anisotropy relative to direction of incident neutrons. What is the influence of this assumption or simplification? Results of Monte Carlo simulation are submitted in this paper. The incorporation of “real” angular energy distribution changes the yield of ²³⁸U fission, and this difference may be compensated by changing the average energy of PFNS in the traditional approach. This effect is connected with correlations between different characteristics of interacted neutrons inside the environment. An additional type of correlation between multiplicity and energy of fission neutrons, named ν-E correlation, is also discussed.

Keywords:

• Fission
• neutron
• spectrum

Acknowledgments

I thank F.-J. Hambsh for sending the data for FF anisotropy and S. Grimes for reading the manuscript and for discussion.