New Experimental 235U(n,f) Prompt Fission Neutron Spectrum and Old Disagreement between Microscopic and Macroscopic Data

Abstract

A measurement of the 235U Prompt Fission Neutron Spectrum (PFNS) was performed at the Budapest Nuclear Research Reactor at 100 oK incident neutron energy. The motivation of this experiment is based on the discrepancy between literature data and the fact that the measured PFNS at thermal incident neutron energy cannot be reproduced by theory. The measured spectra using three neutron detectors are in excellent agreement with each other. The average spectrum confirms literature data within the error bars in the neutron energy range 0.7 - 10 MeV. However, the present PFNS shape cannot predict integral experimental data. It seems to be clear now, that the disagreement between microscopic and macroscopic data is not connected with a systematic experimental error in the PFNS at low incident neutron energy.