Prompt Fission Neutron Emission Spectrum of 235U(n,f) at Thermal Energies

The prompt fission neutron emission spectrum (PFNS) of 235U(n,f) at 100 oK incident neutron energy was measured at the Budapest Reactor. The work was motivated by the discrepancy between literature data and the fact that the measured PFNS at thermal incident neutron energy cannot be reproduced by theory and contradict integral and benchmark experiments [1]. The PFNS was measured by the time-of-flight method with three neutron detectors at different angles, at a flight path length approximately 3 m and a time resolution of 1.7 ns (FWHM). The 235U spectrum was measured simultaneously relative to the 252Cf standard spectrum to avoid systematic errors. Neutron scattering corrections were calculated by the Monte Carlo method. The spectra measured by three neutron detectors are in excellent agreement with each other. The neutron detector efficiencies were calculated by Monte Carlo simulations and compared to the measured ones and show very good agreement. Finally, the resulting average neutron spectrum is in excellent agreement with literature data in the energy range of 0.7 - 10 MeV [2] [3] [4]. Nevertheless, the present PFNS shape cannot predict integral experimental data. These results suggest that the disagreement between microscopic and macroscopic data is not due to a systematic experimental error of the PFNS at low incident neutron energy. [1] D.G. Madland, ISBN-92-64-02134-5, OECD-NEA/WPEC-9, 2003 [2] B.I. Starostov et al., Nejtronnaja Fizika (6th Conf. for Neutron Phys., Kiev, 1983), 1984. T.2.C.285,290,294, EXFOR 40871, 40872, 40873. [3] W. Yufeng et al., Chin. J. Nucl. Phys. 11 (1989) 47, EXFOR 32587. [4] A. Lajtai, IAEA-TECDOC-335, 1985, 312, EXFOR 30704.

FABRY Imrich;  KORNILOV N.;  HAMBSCH Franz-Josef;  OBERSTEDT Stephan;  BELGYA T.;  KIS Z.;  SZENTMIKLOSI L.;  SIMAKOV S.; 

2010-08-11

Commissariat Energie Atomique (CEA)

JRC55666

https://publications.jrc.ec.europa.eu/repository/handle/JRC55666,